The Role of Blue Space in Enhancing Mental Health and Well-Being Among Older Adults: A Systematic Review

Abstract

With the aging global population, understanding the role of blue space (BS) in supporting older adults’ mental health is increasingly important. This systematic review synthesizes quantitative and qualitative evidence to examine how BS influences mental health and well-being in this population. Following PRISMA guidelines, we searched Web of Science, Scopus, PubMed, and PsycINFO for studies published between 2004 and 2024. This review protocol was preregistered on PROSPERO (registration number CRD420250651254). Studies examining BS exposure characteristics and mental health outcomes among adults aged 50 and older were included. A total of twenty-three studies (seventeen quantitative, six qualitative) were reviewed. Quantitative findings indicated generally positive associations between BS proximity, quantity, and improved mental health outcomes, while qualitative findings highlighted the therapeutic benefits of natural features, social interactions, and sensory experiences, along with barriers such as accessibility and safety concerns. BS holds significant potential for promoting older adults’ well-being. These findings highlight the potential of BS as a sustainable urban health resource, offering evidence to support integrated planning strategies that promote environmental, public health, and broader sustainability goals. Future research should investigate specific BS characteristics using longitudinal and experimental designs to enhance causal understanding and inform urban planning and public health strategies.

1. Introduction

By 2050, it is projected that 16% of the global population will be aged 65 and over [1], making population aging one of the most pressing social issues of our time. As people age, there is a gradual decline in physical activity and cognitive function, as well as changes in social roles, family dynamics, and retirement [2]. These changes are frequently accompanied by an increase in physical health issues and mental distress [3,4]. Moreover, the rapid urbanization process has exacerbated feelings of isolation [5,6] and depression [7] among urban-dwelling older adults. These trends highlight the pressing need to prioritize their mental health and well-being [8,9,10].

Some studies have demonstrated that interactions with urban natural environments can increase opportunities for leisure and social activities, thereby improving the mental health and well-being of older adults [11,12,13]. However, physiological and functional changes associated with aging, such as sensory problems (e.g., hearing and vision impairments) [14] and perceived health limitations caused by chronic illnesses [15], present unique challenges for older adults. Unlike younger individuals, older adults are particularly vulnerable to environmental barriers [15]. These changes can significantly limit their participation in daily and outdoor activities, leading to a reduction in their social networks [14]. As a result, older adults may lose the flexibility to adapt to environmental challenges and become more accepting of reduced participation in outdoor activities [16]. These barriers highlight the specific challenges that older adults face in accessing natural environments.

In recent years, growing research has highlighted the significant role of blue space (BS) in promoting human health and well-being, drawing increasing attention from both public health and urban planning fields [17,18]. Building on earlier research exploring how green spaces influence health, scholars have developed similar frameworks to understand the impact of BS on health and well-being [19,20]. Comparably to green space, BS is thought to reduce stress [21,22], promote social interaction [23], increase physical activity [24,25], and mitigate urban heat island effects [26]. However, while green space has been widely studied, research on BS remains limited, particularly regarding vulnerable populations like older adults. This gap suggests the urgent need for deeper exploration of how BS affects older adults’ mental health and well-being. Such research could inform proactive urban interventions and offer valuable guidance for the development of urban public spaces aimed at promoting healthy aging.

Based on investigation, only one systematic review by Wang and Md Sani [27] has explored empirical research on outdoor BS and the health of older adults, concluding that BS can be beneficial to their health. However, the specific physical characteristics of BS that influence older adults’ mental health and well-being remain underexplored. Therefore, this systematic literature review aims to synthesize quantitative and qualitative evidence to understand which specific characteristics of BS are most beneficial to the mental health and well-being of older adults. By reviewing quantitative studies, this review seeks to establish causal relationships between objectively measured BS characteristics and older adults’ mental health outcomes. Moreover, qualitative research is reviewed to gain deeper insights into how these specific characteristics of BS affect older adults’ mental health and well-being. This review also aims to inform urban planners and policymakers on how to design and manage BS to enhance mental health, with a focus on strategies for healthy aging.

Therefore, the present study aims to address the following questions:

(1) What is the existing evidence on specific characteristics of BS that are associated with older adults’ mental health and well-being outcomes?

(2) What are the differences in evidence between quantitative and qualitative studies on the impact of BS on mental health and well-being?

2. Methods

2.1. Search Strategy

This systematic review adhered to the guidelines from the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [28]. Our review protocol was preregistered on PROSPERO (registration number CRD420250651254), and the complete protocol can be accessible at https://www.crd.york.ac.uk/PROSPERO/view/CRD420250651254 (accessed on 24 February 2025). All studies included in this review were searched in July 2024. Articles on related topics were searched in the following four databases: Web of Science, Scopus, PubMed, and PsycINFO. We selected these databases to ensure broad disciplinary coverage and depth. Web of Science and Scopus provide extensive cross-disciplinary citation data [9,29], while PubMed and PsycINFO focus on empirical studies in biomedicine and psychology [30,31]. This combination offers a well-rounded foundation for identifying relevant literature.

Search terms representing BS were drawn from water-related terminology in its core definitions [25,27,32]. Given BS’s frequent overlap with green space, the broader term “green and blue space” was also included. To capture studies on mental health and well-being, we adopted both general (e.g., mental health, well-being) and specific (e.g., stress, depression) terms informed by a prior systematic review [33]. For “older adults”, we used related synonyms as additional search terms.

Table 1. The combination of terms used for article selection.

Main Topics	Search Terms
Blue space	“green and blue space*” OR “blue space*” OR canal OR lake* OR wetland* OR ocean* OR waterfront OR coast* OR coastal OR sea OR freshwater OR “riparian waterway*” OR fountain*
Mental health and well-being	well-being OR well-being OR “subjective wellbeing” OR “subjective well-being” OR stress OR anxiety OR depression OR emotion OR “cognitive function” OR “mental health” OR “life satisfaction”
Older adults	elderly OR “old people” OR “older adults” OR senior* OR elder OR aging

* truncation symbol used to search all possible variations in the word.

presented the terms that were searched in the titles, abstracts, and/or keywords of the articles. We used Boolean logic “AND” and “OR” to search with keyword combinations. We also used some mental health-related Medical Subject Headings (MeSH) terms to increase the precision of this review. A full list of search strings can be found in Supplementary Materials S1. Moreover, the systematic search also included checking the references from eligible articles.

2.2. Eligibility or Selection Criteria

The following criteria were applied to this systematic literature review:

(1) Only articles published between 2004 and 2024 in English were included. Articles published before 2004 were excluded. According to Zhang et al. (2022) [29], BS research was not a prominent area of study before 2005, with only a limited number of publications available before this time.

(2) Only peer-reviewed empirical studies, including quantitative, qualitative, and mixed-methods research, were considered. Literature reviews, books, reports, or materials not indexed in peer-reviewed journals were excluded to ensure the quality of the selected articles.

(3) Selected articles must include reported BS characteristics and examine mental health and well-being outcomes within the broader public health domain. Studies that did not distinguish between blue and green spaces were excluded. Likewise, studies focusing exclusively on severe mental illness were also excluded from the scope of this review.

(4) Research articles must focus on older adults or primarily include participants aged 50 years and above, as this group (aged 50–64 years) is often considered pre-elderly and included in aging studies [34,35]. While the traditional definition of older adults generally refers to individuals aged 60 and above [36], broader classifications also encompass pre-retirement and late middle-aged groups [31]. To better understand the aging process, many large-scale longitudinal studies, such as the English Longitudinal Study of aging [37] and the Whitehall II cohort study [38] have typically recruited participants from age 50 onwards. Therefore, this review included studies with a mean participant age of 50 years or older.

(5) Eligible studies had to examine the relationship between BS environments and the mental health and well-being of older adults. This review aimed to identify which BS characteristics influence these outcomes. Studies involving direct or indirect exposure to BS were included, whereas those focused solely on BS features (e.g., water quality, flooding) or specific mental health issues (e.g., post-disaster psychological trauma) were excluded.

2.3. Data Extraction and Synthesis

All records were imported into Zotero, where duplicates, non-English, and non-research articles were removed. One author (J.G.) first excluded clearly irrelevant records. Two authors (J.G. and S.B.I.) then independently screened titles and abstracts, followed by repeated full-text reviews to confirm eligibility. Any disagreements were resolved in consultation with the other three authors (S.A.S., N.B.H., and W.S.W.M.). Key findings from eligible studies were systematically recorded and tabulated (see Table 2). Extracted information included author, publication year, country, study design, population, sample size, BS types and measurement, mental health and well-being outcomes and measurement, covariates or mediators (if applicable), main results, and quality assessment.

Specific characteristics of BS were extracted from the included articles, referencing other studies from environmental and public health research [20,30,39]. The characteristics of BS in quantitative studies were classified into four main categories: quantity, objective quality, perceived quality, and exposure characteristics. For qualitative studies, thematic analysis was performed, and the following five themes were extracted: natural features, facilities, senses, barriers, and social connection and activities.

Table 2. Main characteristics and results on blue space and the older adults’ mental health and well-being.

Author, Year, Country	Study Design	Population	Sample Size	BS Types	BS Measurement	Mental Health and Well-Being Outcomes	Outcomes Measurement	Covariates, Moderators or Mediators	Main Results	Quality Assessment
Y. Chen and Yuan [40], 2020, China	Cross-sectional study	60–90 years	966	Rivers, lakes, streams and others (F)	NDWI, proportion, per capita water area, PSI, proximity, accessibility (observation by street views and field survey)	GMH	SF-36	Covariates: age, gender, education, marital status, hukou, income and occupation Mediators: air pollution, stress, physical activity duration, social contact	Positive correlation between hydrophilicity and GMH, where stress functioned as a mediator. Negative correlation between per capita water area and GMH.	High
Garrett et al. [41], 2019, China	Cross-sectional study	18–70 years (80% > 50 years)	1000	Inland aquatic areas and coastal areas (F& O)	Questionnaire (BS expose, perceived qualities, duration and activities)	GMH, SWB and recalled well-being (momentary SWB)	Self-rated general health, WHO-5 and 4 items of MENE	Covariates: age, gender, income and occupation, physical functioning, physical activity levels, and availability of private outdoor spaces	Indirect BS exposure enhanced GMH, while 15 min walk accessibility remained insignificant. Weekly visits improved SWB, with recalled well-being linked to 60–120 min visits, high activity levels, safety, and wildlife presence.	Middle
Zhifeng and Yin [42], 2021, China	Cross-sectional study	>60 years	757	Urban water surfaces (F)	MNDWI	Depression	GDS-15	Covariates: age, gender, education, marital status, Hukou; Mediator: non-communicable chronic disease	MNDWI showed statistically significant associations with GDS-15 within 100 m.	High
Helbich et al. [43], 2019, China	Cross-sectional study	>60 years	1190	Rivers, lakes and other water features (F)	BS street view and NDWI	Depression	GDS-15	Covariates: age, education, ethnicity, marital status, Party membership, hukou status, functional ability, physical health status, air pollution	BS street view was negatively associated with the elderly’s depression, and NDWI was not associated with depression.	High
McDougall et al. [3], 2021, Scotland	Cross-sectional study	>50 years	6976	Freshwater BS, large freshwater lakes, and coastal BS (F& O)	The percentage of freshwater Surface area coverage within 800 m (immediate) and 1600 m (wider) neighborhood buffers, distance to the nearest large freshwater lake and coastline	Depression	Antidepressant prescription records from the Prescribing Information System for Scotland	Public and total GS coverage, sex, age, proportion of state pension, low-income households, overcrowding, and crime rate	Older adults residing near substantial freshwater BS (>3% coverage) and within 1 km of major lakes or coastal areas showed reduced antidepressant usage rates.	High
Cerin et al. [44], 2022, Australia	Cross-sectional study	≥25 years, the average age was 61 years	4141	Lakes, coastal BS and rivers (F& O)	BS proportion within 1000 m buffers around geocoded residential addresses	Cognitive function	CVLT and SDMT	Covariates: sex, age, education, employment status, household income, living arrangements, ethnicity, health-related diseases and behaviors, environment	While BS showed no direct impact on cognitive performance, beneficial indirect effects emerged via waist circumference, HDL cholesterol, and glycated hemoglobin levels (particularly in diabetic patients).	High
Qiu et al. [45], 2021, China	Cross-sectional study	>60 years	300	Lakes (F)	Photos of water, Questionnaire (PSD)	Restoration	PRS	Socio-demographic characteristics (sex and age)	BS had a higher restorative potential. (serene, refuge and prospect)	Middle
Aliyas [46], 2021, Iran	Cross-sectional study	≥65 years	912	Coastal Parks (O)	Questionnaire (access to coastal parks, visitation frequency, length of stay, physical activity level)	GMH	MOS SF-20	Control variables: age, gender, marital status, occupation, education	Length of time spent in BS and level of physical activity were positively correlated with the elderly’s mental health.	High
Vegaraju and Amiri [47], 2024, USA	Cross-sectional study	≥65 years	42,980	Water bodies (F&O)	The Euclidean distance from the centroid of Census blocks to the nearest BS (proximity)	Serious psychological distress, GMH, QOL	K6, Self-rated general health, HRQOL-4	Control variables: age, gender, race/ethnicity, education	Proximity to BS correlated with improved GMH and reduced likelihood of serious psychological distress.	High
Soloveva et al. [48], 2024, Australia	Cross-sectional study	≥25 years, average age was 61 years	4141	Water surface (Lakes, coastlines, rivers, reservoirs) (F&O)	BS proportion within 1000 m street-network buffers in neighborhoods	Depression	CES-D	Age, sex, education, marital status, income, employment status, health-related diseases and behaviors, neighborhood socioeconomic status, environment	No significant associations were found between BS and depressive symptoms.	Middle
Fangfang et al. [49], 2021, China	Cross-sectional study	≥60 years	5848 participants (response rate 94.16%)	Lakes and rivers (F)	Percentage of BS within 800 m buffers around the residence, identified using Open Street Map data	Cognitive function	MMSE and MCI	Sociodemographic factors, health-related behaviors, chronic conditions, depression symptoms, body mass index	The presence of BS within 800 m was linked to higher MMSE scores in females but showed no association with MCI.	High
Huang et al. [50], 2022, China	Cross-sectional study	≥60 yeasrs	301,442	Freshwater BS, oceanic BS (F&O)	The percentage of BS (overall BS, freshwater BS, oceanic BS) within a 1000 m buffer, the Euclidean distance to the nearest BS (overall BS, freshwater BS, oceanic BS)	GMH	Self-reported general health	Urbanicity, neighborhood social deprivation, gender, age, education, type of housing (public/private)	Coastal proximity improved older adults’ self-rated health in both private and public housing. However, BS percentage and freshwater proximity only benefited those in private housing.	High
Mavoa et al. [51], 2019, Australia	Cross-sectional study	≥18 years, the average age was 54.6 years	4912	Water surface (F&O)	The straight-line distance from the participants’ residences to the nearest coastline, water area percentages (inland and marine) across 400 m, 800 m, and 1600 m buffer zones	SWB	the Australian Unity well-being Index	Socio-demographic characteristics, index of relative socio-economic disadvantage, greenspace visit frequency	No direct association was found between BS and SWB.	High
Poulsen et al. [52], 2022, USA	Cross-sectional study (Mix)	the average age was 58 years	1122	Freshwater bodies (F)	FBS visit characteristics	Restoration, perceived stress, GMH, life satisfaction	6 items of ROS, PSS-10, part of SF-36, a single question	Age, sex, education, physical activity frequency, general health, and presence of children in the household	More frequent visits to FBS were associated with higher restoration and lower perceived stress but were not associated with GMH and overall life satisfaction.	High
Dempsey et al. [13], 2018, Ireland	Cross-sectional study	>50 years	8504	Coastal BS (O)	Euclidean distance from old adults’ residences to the coastline (proximity), proportion of visible coastal BS within 10 km of coastline (visibility)	Depression	CES-D	Self-rated vision, anti-depressant medication, age, gender, marital status, employment status, income, health-related behaviors, social connectedness score and population density	Older adults who lived closer to coastal BS had lower depression risks. Having the greatest sea view was associated with a significant positive effect on lower depression outcomes.	High
Klompmaker et al. [53], 2022, USA	Longitudinal study (cohort study)	fee-for-service Medicare beneficiaries ≥65 years	about 61.7 million	Surface water (F&O)	Proportion of BS within residential zip code areas and 1000 m buffer zones	ADRD and PD	Initial hospital admissions with a primary or secondary diagnosis of ADRD or PD upon discharge	Covariates: Individual-level: age, gender, racial/ethnic background, Medicaid status, entry year, and residential location; Area-level: meteorological and air pollution indicators	Higher BS coverage correlated with reduced PD hospitalization rates, while showing no significant effect on ADRD hospitalization rates.	High
B.-P. Liu et al. [54], 2024, UK	Longitudinal study (cohort study)	56.7 years	363,047	Water surface (F&O)	BS percentage within 300 m and 1000 m buffers around each residential location	Presence of specific or any psychiatric disorder diagnoses	The first diagnoses of any or specific mental disorders (obtained from the UKB)	Age, sex, socioeconomic factors, ethnicity, body mass index, smoking and alcohol consumption, physical activity, history of hypertension, and type 2 diabetes	Increased BS coverage demonstrated significant risk reduction for any psychiatric disorder, with anxiety incidence specifically linked to BS within 1000 m buffer zones.	High
Coleman and Kearns [55], 2015, New Zealand	Qualitative study	65–94 years	28	Island (O)	Participatory photo-elicitation	Experiences of place, being aged, and well-being	In-depth interviews, participant journals	Not Applicable	Although island settings pose unique challenges for older adults, BS helps maintain their well-being.	High
Finlay et al. [56], 2015, Canada	Qualitative study	65–86 years	27 in 2012; with 19 in 2013	Ocean (O)	Walk the talk (around PN)	Perceived health	In-depth interviews	Not Applicable	BS served as restorative environments that alleviated stress and fostered spiritual connections among older adults.	High
Pool et al. [57], 2023, England	Qualitative study	50–75 years	8	Ocean (O)	photographs of BS	Social connections, recuperation and escape (coastal community group)	Semi-structured interviews	Not Applicable	BS provided therapeutic advantages, promoting older adults’ mental tranquility, mindfulness, and psychological restoration.	High
Costello et al. [58], 2019, Australia	Qualitative study	55 years and above	17	Ocean (O)	Self-organized ocean swimming interviews, Field notes	General health, social and psychological benefits (Self-organized ocean swimming group)	In-person interviews, Observer participation, Field notes	Not Applicable	Swimming in BS enhanced social connections and increased health and well-being.	High
Kreutz [59], 2024, USA	Qualitative study	65–85 years	21	Lakes and wetlands (F)	photographs and maps of BS	restoration experiences, intergenerational connection	Semi-structured interviews	Not Applicable	The affordance of BS provided older adults with restorative, interpersonal opportunities and intergenerational connections.	High
Duedahl et al. [60], 2022, Denmark	Qualitative study	55 years and above	48	the Danish Wadden Sea National Park (O)	Subjective experiences	Increased physical activity, mental well-being, spiritual health	Interviews (go-along method and sedentary)	Not Applicable	Dynamic and continuous engagement with nature evoked older adults’ childish feelings.	High
Notes: Space types: F: Freshwater; O: Ocean; BS: Blue space; FBS: Freshwater blue space; GS: Green space Blue space measurements: PSI: Patch Separation Index; NDWI: Normalized Difference Water Index; MNNDWI: Modified Normalized Difference Water Index Mental health and well-being outcomes: GMH: General Mental Health; SWB: Subjective Well-being; ADRD: Alzheimer’s Disease and Related Dementias; PD: Parkinson’s Disease; QOL: Quality of Life Mental health and well-being outcomes measurements: SF-36: 36-item Short Form Health Survey (36 items); WHO-5: World Health Organization’s 5-Item Well-being Index; MENE: English Monitor of Engagement with the Natural Environment Survey; GDS-15: Geriatric Depression Scale; CES-D: Center for Epidemiologic Studies Depression Scale; CVLT: California Verbal Learning Test; SDMT: Symbol Digit Modalities Test; PSD: Perceived Sensory Dimensions; PRS: Perceived Restorativeness Scale; MOS SF-20: the Rand Medical Outcomes Study Health Survey; HRQOL-4: Health-Related Quality of Life and Well-Being; MMSE: Mini Mental State Examination; MCI: Mild Cognitive Impairment; ROS: Restoration Outcome Scale; PSS-10: Perceived Stress Scale; K6: Kessler 6 Psychological Distress Scale

Table 2. Main characteristics and results on blue space and the older adults’ mental health and well-being.

Author, Year, Country	Study Design	Population	Sample Size	BS Types	BS Measurement	Mental Health and Well-Being Outcomes	Outcomes Measurement	Covariates, Moderators or Mediators	Main Results	Quality Assessment
Y. Chen and Yuan [40], 2020, China	Cross-sectional study	60–90 years	966	Rivers, lakes, streams and others (F)	NDWI, proportion, per capita water area, PSI, proximity, accessibility (observation by street views and field survey)	GMH	SF-36	Covariates: age, gender, education, marital status, hukou, income and occupation Mediators: air pollution, stress, physical activity duration, social contact	Positive correlation between hydrophilicity and GMH, where stress functioned as a mediator. Negative correlation between per capita water area and GMH.	High
Garrett et al. [41], 2019, China	Cross-sectional study	18–70 years (80% > 50 years)	1000	Inland aquatic areas and coastal areas (F& O)	Questionnaire (BS expose, perceived qualities, duration and activities)	GMH, SWB and recalled well-being (momentary SWB)	Self-rated general health, WHO-5 and 4 items of MENE	Covariates: age, gender, income and occupation, physical functioning, physical activity levels, and availability of private outdoor spaces	Indirect BS exposure enhanced GMH, while 15 min walk accessibility remained insignificant. Weekly visits improved SWB, with recalled well-being linked to 60–120 min visits, high activity levels, safety, and wildlife presence.	Middle
Zhifeng and Yin [42], 2021, China	Cross-sectional study	>60 years	757	Urban water surfaces (F)	MNDWI	Depression	GDS-15	Covariates: age, gender, education, marital status, Hukou; Mediator: non-communicable chronic disease	MNDWI showed statistically significant associations with GDS-15 within 100 m.	High
Helbich et al. [43], 2019, China	Cross-sectional study	>60 years	1190	Rivers, lakes and other water features (F)	BS street view and NDWI	Depression	GDS-15	Covariates: age, education, ethnicity, marital status, Party membership, hukou status, functional ability, physical health status, air pollution	BS street view was negatively associated with the elderly’s depression, and NDWI was not associated with depression.	High
McDougall et al. [3], 2021, Scotland	Cross-sectional study	>50 years	6976	Freshwater BS, large freshwater lakes, and coastal BS (F& O)	The percentage of freshwater Surface area coverage within 800 m (immediate) and 1600 m (wider) neighborhood buffers, distance to the nearest large freshwater lake and coastline	Depression	Antidepressant prescription records from the Prescribing Information System for Scotland	Public and total GS coverage, sex, age, proportion of state pension, low-income households, overcrowding, and crime rate	Older adults residing near substantial freshwater BS (>3% coverage) and within 1 km of major lakes or coastal areas showed reduced antidepressant usage rates.	High
Cerin et al. [44], 2022, Australia	Cross-sectional study	≥25 years, the average age was 61 years	4141	Lakes, coastal BS and rivers (F& O)	BS proportion within 1000 m buffers around geocoded residential addresses	Cognitive function	CVLT and SDMT	Covariates: sex, age, education, employment status, household income, living arrangements, ethnicity, health-related diseases and behaviors, environment	While BS showed no direct impact on cognitive performance, beneficial indirect effects emerged via waist circumference, HDL cholesterol, and glycated hemoglobin levels (particularly in diabetic patients).	High
Qiu et al. [45], 2021, China	Cross-sectional study	>60 years	300	Lakes (F)	Photos of water, Questionnaire (PSD)	Restoration	PRS	Socio-demographic characteristics (sex and age)	BS had a higher restorative potential. (serene, refuge and prospect)	Middle
Aliyas [46], 2021, Iran	Cross-sectional study	≥65 years	912	Coastal Parks (O)	Questionnaire (access to coastal parks, visitation frequency, length of stay, physical activity level)	GMH	MOS SF-20	Control variables: age, gender, marital status, occupation, education	Length of time spent in BS and level of physical activity were positively correlated with the elderly’s mental health.	High
Vegaraju and Amiri [47], 2024, USA	Cross-sectional study	≥65 years	42,980	Water bodies (F&O)	The Euclidean distance from the centroid of Census blocks to the nearest BS (proximity)	Serious psychological distress, GMH, QOL	K6, Self-rated general health, HRQOL-4	Control variables: age, gender, race/ethnicity, education	Proximity to BS correlated with improved GMH and reduced likelihood of serious psychological distress.	High
Soloveva et al. [48], 2024, Australia	Cross-sectional study	≥25 years, average age was 61 years	4141	Water surface (Lakes, coastlines, rivers, reservoirs) (F&O)	BS proportion within 1000 m street-network buffers in neighborhoods	Depression	CES-D	Age, sex, education, marital status, income, employment status, health-related diseases and behaviors, neighborhood socioeconomic status, environment	No significant associations were found between BS and depressive symptoms.	Middle
Fangfang et al. [49], 2021, China	Cross-sectional study	≥60 years	5848 participants (response rate 94.16%)	Lakes and rivers (F)	Percentage of BS within 800 m buffers around the residence, identified using Open Street Map data	Cognitive function	MMSE and MCI	Sociodemographic factors, health-related behaviors, chronic conditions, depression symptoms, body mass index	The presence of BS within 800 m was linked to higher MMSE scores in females but showed no association with MCI.	High
Huang et al. [50], 2022, China	Cross-sectional study	≥60 yeasrs	301,442	Freshwater BS, oceanic BS (F&O)	The percentage of BS (overall BS, freshwater BS, oceanic BS) within a 1000 m buffer, the Euclidean distance to the nearest BS (overall BS, freshwater BS, oceanic BS)	GMH	Self-reported general health	Urbanicity, neighborhood social deprivation, gender, age, education, type of housing (public/private)	Coastal proximity improved older adults’ self-rated health in both private and public housing. However, BS percentage and freshwater proximity only benefited those in private housing.	High
Mavoa et al. [51], 2019, Australia	Cross-sectional study	≥18 years, the average age was 54.6 years	4912	Water surface (F&O)	The straight-line distance from the participants’ residences to the nearest coastline, water area percentages (inland and marine) across 400 m, 800 m, and 1600 m buffer zones	SWB	the Australian Unity well-being Index	Socio-demographic characteristics, index of relative socio-economic disadvantage, greenspace visit frequency	No direct association was found between BS and SWB.	High
Poulsen et al. [52], 2022, USA	Cross-sectional study (Mix)	the average age was 58 years	1122	Freshwater bodies (F)	FBS visit characteristics	Restoration, perceived stress, GMH, life satisfaction	6 items of ROS, PSS-10, part of SF-36, a single question	Age, sex, education, physical activity frequency, general health, and presence of children in the household	More frequent visits to FBS were associated with higher restoration and lower perceived stress but were not associated with GMH and overall life satisfaction.	High
Dempsey et al. [13], 2018, Ireland	Cross-sectional study	>50 years	8504	Coastal BS (O)	Euclidean distance from old adults’ residences to the coastline (proximity), proportion of visible coastal BS within 10 km of coastline (visibility)	Depression	CES-D	Self-rated vision, anti-depressant medication, age, gender, marital status, employment status, income, health-related behaviors, social connectedness score and population density	Older adults who lived closer to coastal BS had lower depression risks. Having the greatest sea view was associated with a significant positive effect on lower depression outcomes.	High
Klompmaker et al. [53], 2022, USA	Longitudinal study (cohort study)	fee-for-service Medicare beneficiaries ≥65 years	about 61.7 million	Surface water (F&O)	Proportion of BS within residential zip code areas and 1000 m buffer zones	ADRD and PD	Initial hospital admissions with a primary or secondary diagnosis of ADRD or PD upon discharge	Covariates: Individual-level: age, gender, racial/ethnic background, Medicaid status, entry year, and residential location; Area-level: meteorological and air pollution indicators	Higher BS coverage correlated with reduced PD hospitalization rates, while showing no significant effect on ADRD hospitalization rates.	High
B.-P. Liu et al. [54], 2024, UK	Longitudinal study (cohort study)	56.7 years	363,047	Water surface (F&O)	BS percentage within 300 m and 1000 m buffers around each residential location	Presence of specific or any psychiatric disorder diagnoses	The first diagnoses of any or specific mental disorders (obtained from the UKB)	Age, sex, socioeconomic factors, ethnicity, body mass index, smoking and alcohol consumption, physical activity, history of hypertension, and type 2 diabetes	Increased BS coverage demonstrated significant risk reduction for any psychiatric disorder, with anxiety incidence specifically linked to BS within 1000 m buffer zones.	High
Coleman and Kearns [55], 2015, New Zealand	Qualitative study	65–94 years	28	Island (O)	Participatory photo-elicitation	Experiences of place, being aged, and well-being	In-depth interviews, participant journals	Not Applicable	Although island settings pose unique challenges for older adults, BS helps maintain their well-being.	High
Finlay et al. [56], 2015, Canada	Qualitative study	65–86 years	27 in 2012; with 19 in 2013	Ocean (O)	Walk the talk (around PN)	Perceived health	In-depth interviews	Not Applicable	BS served as restorative environments that alleviated stress and fostered spiritual connections among older adults.	High
Pool et al. [57], 2023, England	Qualitative study	50–75 years	8	Ocean (O)	photographs of BS	Social connections, recuperation and escape (coastal community group)	Semi-structured interviews	Not Applicable	BS provided therapeutic advantages, promoting older adults’ mental tranquility, mindfulness, and psychological restoration.	High
Costello et al. [58], 2019, Australia	Qualitative study	55 years and above	17	Ocean (O)	Self-organized ocean swimming interviews, Field notes	General health, social and psychological benefits (Self-organized ocean swimming group)	In-person interviews, Observer participation, Field notes	Not Applicable	Swimming in BS enhanced social connections and increased health and well-being.	High
Kreutz [59], 2024, USA	Qualitative study	65–85 years	21	Lakes and wetlands (F)	photographs and maps of BS	restoration experiences, intergenerational connection	Semi-structured interviews	Not Applicable	The affordance of BS provided older adults with restorative, interpersonal opportunities and intergenerational connections.	High
Duedahl et al. [60], 2022, Denmark	Qualitative study	55 years and above	48	the Danish Wadden Sea National Park (O)	Subjective experiences	Increased physical activity, mental well-being, spiritual health	Interviews (go-along method and sedentary)	Not Applicable	Dynamic and continuous engagement with nature evoked older adults’ childish feelings.	High
Notes: Space types: F: Freshwater; O: Ocean; BS: Blue space; FBS: Freshwater blue space; GS: Green space Blue space measurements: PSI: Patch Separation Index; NDWI: Normalized Difference Water Index; MNNDWI: Modified Normalized Difference Water Index Mental health and well-being outcomes: GMH: General Mental Health; SWB: Subjective Well-being; ADRD: Alzheimer’s Disease and Related Dementias; PD: Parkinson’s Disease; QOL: Quality of Life Mental health and well-being outcomes measurements: SF-36: 36-item Short Form Health Survey (36 items); WHO-5: World Health Organization’s 5-Item Well-being Index; MENE: English Monitor of Engagement with the Natural Environment Survey; GDS-15: Geriatric Depression Scale; CES-D: Center for Epidemiologic Studies Depression Scale; CVLT: California Verbal Learning Test; SDMT: Symbol Digit Modalities Test; PSD: Perceived Sensory Dimensions; PRS: Perceived Restorativeness Scale; MOS SF-20: the Rand Medical Outcomes Study Health Survey; HRQOL-4: Health-Related Quality of Life and Well-Being; MMSE: Mini Mental State Examination; MCI: Mild Cognitive Impairment; ROS: Restoration Outcome Scale; PSS-10: Perceived Stress Scale; K6: Kessler 6 Psychological Distress Scale

The review covered diverse mental health and well-being outcomes, spanning from overall mental health to short-term emotional responses (see

Table 3. Summary of mental health and well-being categories.

Mental Health and Well-Being	Number of Studies	Tools	Authors
General mental health	6	SF36	Y. Chen and Yuan [40] Poulsen et al. [52]
		One single question	Huang et al. [50] Vegaraju and Amiri [47] Garrett et al. [41]
		MOS SF-20	Aliyas [46]
Depression	5	GDS-15	Zhifeng and Yin [42] Helbich et al. [43]
		CES-D	Dempsey et al. [13] Soloveva et al. [48]
		Antidepressant prescription data	McDougall et al. [3]
Subjective well-being	3	the Australian Unity Well-being Index	Mavoa et al. [51]
		WHO-5, MENE	Garrett et al. [41]
		One single question	Poulsen et al. [52]
Specific mental disorder	2	First hospital admissions or diagnoses	Klompmaker et al. [53] B.-P. Liu et al. [54]
Cognitive function	2	CVLT and SDMT	Cerin et al. [44]
		MMSE and MCI	Fangfang et al. [49]
Restoration	2	PRS	Qiu et al. [45]
		ROS	Poulsen et al. [52]
Psychological distress	1	K6	Vegaraju and Amiri [47]
Quality of life	1	HRQOL-4	Vegaraju and Amiri [47]
Perceived stress	1	PSS-10	Poulsen et al. [52]
Short-term emotion	6	Not Applicable	Coleman and Kearns [55] Finlay et al. [56] Pool et al. [57] Costello et al. [58] Kreutz [59] Duedahl et al. [60]
Notes: SF-36: 36-item Short Form Health Survey (36 items); MOS SF-20: the Rand Medical Outcomes Study Health Survey; GDS-15: Geriatric Depression Scale; CES-D: Center for Epidemiologic Studies Depression Scale; WHO-5: World Health Organization’s 5-Item Well-being Index; MENE: English Monitor of Engagement with the Natural Environment Survey; CVLT: California Verbal Learning Test; SDMT: Symbol Digit Modalities Test; PSD: Perceived Sensory Dimensions; MMSE: Mini Mental State Examination; MCI: Mild Cognitive Impairment; PRS: Perceived Restorativeness Scale; ROS: Restoration Outcome Scale; K6: Kessler 6 Psychological Distress Scale; HRQOL-4: Health-Related Quality of Life and Well-Being; PSS-10: Perceived Stress Scale

). Due to the high heterogeneity in both the BS characteristics as well as mental health and well-being outcomes, a meta-analysis was not conducted, and the study results were presented in a narrative synthesis report.

The research outcomes were categorized into quantitative (cross-sectional and longitudinal) and qualitative outcomes and organized based on different study designs. Additionally, specific domains of mental health and well-being, along with their measurement tools, were reported. In quantitative studies, associations between BS characteristics and older adults’ mental health and well-being were classified as positive, negative, or non-significant. Positive associations indicated links between BS, improved mental health and well-being outcomes, while negative associations suggested adverse effects. Non-significant associations implied no observable relationship. If multiple statistical models were present, only the results from the adjusted models were considered. For qualitative findings, as they are typically not derived through statistical methods, thematic analysis was conducted.

2.4. Quality Assessment

The quality of the included articles was assessed using the Joanna Briggs Institute (JBI) Critical Appraisal Checklists, which provide evaluation criteria tailored to different study designs. Specifically, cross-sectional [61] (15 studies), cohort [61] (two studies), and qualitative [62] (six studies) studies were appraised using their respective JBI checklists. Each study underwent a critical appraisal based on these criteria, with ratings of “Yes”, “No”, “Unclear”, or “Not Applicable” assigned to capture methodological rigor and potential sources of bias (see Supplementary Materials S2).

The final quality ratings of the included studies were considered in the synthesis of this systematic review. Most of the studies (n = 20) were classified as high quality and thus played a more substantial role in shaping the analysis. Any discrepancies in scoring were resolved through discussion until consensus was reached, ensuring a rigorous and consistent evaluation process.

3. Results

3.1. Study Selection

The database search initially identified 7432 potentially relevant records, with two additional studies retrieved through reference list screening. After a thorough deduplication process and screening of titles and abstracts, 154 publications were selected for full-text assessment. Following a systematic evaluation, 23 articles met the eligibility criteria for inclusion in this systematic review. The complete study selection process is illustrated in Figure 1.

3.2. Study Characteristics

This systematic literature review ultimately included 23 articles, comprising 17 quantitative studies, including one mixed-method study categorized as a quantitative study due to its presentation of results [52], and six qualitative studies. Among these, eight studies were conducted in Asia (China: seven, Iran: one), five in Europe (Ireland: one, Scotland: one, UK: one, England: one, Denmark: one), five in North America (USA: four, Canada: one), and five in Oceania (Australia: four, New Zealand: one). There is currently a notable lack of evidence from lower- and middle-income countries, particularly in tropical regions, South America, and Africa. Asia contributes the largest share of evidence, with 87.5% (n = seven) of studies from China, yet longitudinal and qualitative research remains limited. Additionally, the United States and Australia contributed the second-largest body of evidence. All included articles were published after 2015. About 70% of articles (n = 16) were published in the past five years, highlighting the rapid growth of this relatively emerging field in BS research.

Among the quantitative studies, 15 studies were cross-sectional, and two were longitudinal. The sample sizes ranged widely from 300 [45] to about 61.7 million [53]. All six qualitative studies employed interviews, with the numbers of participants ranging from 8 to 48.

Table 3 shows the number of included studies categorized by type of mental health and well-being outcomes. The seventeen quantitative studies examined outcomes such as general mental health (six studies), depression (five), subjective well-being (three), specific mental disorders (two), cognitive function (two), restoration (two), psychological distress (one), quality of life (one), and perceived stress (one). Seventeen distinct tools were used to measure these outcomes, with SF-36, GDS-15, and CES-D being the most frequently employed across multiple studies. A total of 14 studies relied on self-reported data, while two utilized hospital admissions or diagnoses data, and one employed prescription data. All six qualitative studies focused on short-term emotional aspects of mental well-being, as reported through interviews.

3.3. Blue Space Characteristics

Among the 17 quantitative studies included, the majority (n = 14) objectively measured the physical characteristics of BS, with a primary focus on quantity and quality. For quantity, eight studies quantified the proportion of water areas within specific regions, while three employed the Normalized Difference Water Index (NDWI) [40,43] and the Modified Normalized Difference Water Index (MNDWI) [42]. Regarding quality, proximity to the nearest water body was examined in six studies, making it another frequently assessed characteristic. Visibility, though rarely examined, was assessed in two studies, focusing on street views and the general visibility of BS [13,43]. Connectivity was investigated in one study using the Patch Separation Index, providing insights into the spatial distribution and fragmentation of BS [40]. Beyond these objective measures, five studies incorporated subjective evaluations to examine perceived quality and exposure characteristics of BS.

All six qualitative studies explored participants’ experiences and interactions with BS. Three studies involved researchers engaging in BS-related activities with participants to capture their perspectives, including walk-along interviews [56,60] and post-swimming interviews [58]. Two studies utilized visual-based methods: participants took photographs of BS themselves [55], or researchers presented pre-selected images of local BS for participant discussion [57]. In another study, Kreutz [59] asked participants to map specific BS features and identify barriers to their use.

3.4. Quantitative Evidence on Blue Space and Older Adults’ Mental Health and Well-Being

The quantitative studies reviewed reported diverse findings due to varying BS characteristics and mental health outcomes, which made it complicated to directly compare across studies. A descriptive analysis was conducted to examine specific BS characteristics and their associations with older adults’ mental health and well-being (see

Table 4. Overview of the quantitative findings regarding blue space characteristics associated with mental health and well-being.

BS Characteristics	Mental Health and Well-Being from Quantitative Studies
	+ Positive	0 Non-Significant	− Negative
Quantity (10 studies)
NDWI and MNDWI (3 studies)	Depression (MNDWI) [42]	GMH (NDWI) [40] Depression (NDWI) [43]
Proportion of water area (8 studies)	Depression [3] PD [53] Cognitive function [44] Cognitive function–MMSE [49] Special mental disorder [54]	GMH [40] Depression [48] ADRD [53] Cognitive function–MCI [49] SWB [51]
Per capita water area (1 study)			GMH [40]
Objective quality (7 studies)
Proximity (6 studies)	Serious psychological distress [47] GMH [47,50] Depression [3,13]	GMH [40] SWB [51] Quality of life [47]
Visibility (2 studies)	Depression [13]		Depression [43]
Connectivity (1 study)		GMH [40]
Hydrophilicity (1 study)	GMH [40]
Perceived quality (3 studies)
Access to BS (2 studies)		GMH [41,46] SWB [41]
BS quality (2 studies)	Recalled well-being (wildlife, safe) [41] Restoration (esthetics) [45]	Recalled well-being (facilities quality) [41]
Exposure characteristics (3 studies)
Exposure way (1 study)	GMH (indirect exposure) [41] SWB (intentional exposure) [41]
Frequency (3 studies)	SWB (once a week) [41] Restoration [52] Perceived stress [52]	GMH [46,52] Life satisfaction [52]
Duration (2 studies)	Recalled well-being (60–120 min) [41] GMH [46]
Activities (2 studies)	Recalled well-being (high activity intensity) [41] GMH (level of physical activity) [46]
Notes: NDWI: Normalized Difference Water Index; MNDWI: Modified Normalized Difference Water Index GMH: General mental health; SWB: Subjective well-being; ADRD: Alzheimer disease and related dementias; PD: Parkinson’s disease; MMSE: Mini Mental State Examination; MCI: Mild Cognitive Impairment

).

3.4.1. Evidence from Quantity

Among the studies on quantity, the proportion of water areas was the most frequently examined BS characteristic. Five studies showed statistically significant positive associations between the proportion of water areas and mental health. Researchers observed within buffer zones ranging from 800 to 1600 m, and the strongest effects were typically noted within 800 to 1000 m. For example, four studies found positive correlations within a 1000 m buffer [44,50,53,54]. McDougall et al. [3] identified significant links between freshwater BS coverage and lower antidepressant medication prevalence within 800 and 1600 m. Similarly, Fangfang et al. [49] identified positive links between the proportion of BS and cognitive function in women within 800 m.

Conversely, five studies found no significant associations between BS and mental health outcomes. Y. Chen and Yuan [40], Klompmaker et al. [53], and Soloveva et al. [48] reported no relationship between the proportion of water areas within a 1000 m buffer and general mental health, ADRD hospitalization, and depression. Similarly, Mavoa et al. [51] found no significant links between water area and subjective well-being across buffer zones of 400, 800, or 1600 m.

Three studies investigated the relationship between NDWI and MNDWI and mental health outcomes. Zhifeng and Yin [42] identified significant associations between MNDWI and depression, while Y. Chen and Yuan [40] and Helbich et al. [43] found no significant effects on general mental health outcomes. Additionally, Y. Chen and Yuan [40] observed a negative correlation.

3.4.2. Evidence from Objective Quality

Proximity was the second most frequently assessed BS characteristic, with four reporting significant associations. Dempsey et al. [13] found that older adults living closer to the Irish coastline had a reduced likelihood of experiencing depression, while McDougall et al. [3] observed lower antidepressant prescriptions among those living within 1000 m of large freshwater lakes or coastal areas. Positive associations between BS proximity and general mental health were also noted by Huang et al. [50] and Vegaraju and Amiri [47]. Vegaraju and Amiri [47] also reported the positive association with serious psychological distress. However, three studies found no significant relationships between proximity and mental health outcomes [40,47,51].

Two studies explored visibility—a less commonly studied BS characteristic. Dempsey et al. [13] reported that greater coastal visibility from respondents’ homes was associated with lower odds of depression. In contrast, Helbich et al. [43] found a negative correlation between BS visibility and depressive symptoms using convolutional neural networks to analyze street view images.

One study [40] assessed hydrophilicity through field surveys and street view observations, reporting a strong link to general mental health outcomes. In contrast, the study did not indicate any clear relationship between BS quality (measured using the patch separation index) and general mental health outcomes.

3.4.3. Evidence from Perceived Quality

Three studies investigated the perceived quality of BS using survey data, with two reporting no significant associations. Aliyas [46] assessed park accessibility within a 10 min walking distance from respondents’ homes, while Garrett et al. [41] evaluated perceived proximity within a 15 min walking distance to BS.

Perceived general quality was assessed in two studies. Garrett et al. [41] identified positive associations between perceived safety, wildlife presence, and recalled well-being but found no links with facility quality or cleanliness. Qiu et al. [45] reported that esthetics positively influenced restorative experiences among older adults.

3.4.4. Evidence from Exposure Characteristics

One study [41] found that regular visits to BS (once a week) were significantly associated with improved subjective well-being, while indirect exposure, such as viewing BS from home, was correlated with better self-reported health.

Three studies examined visit frequency and duration, yielding mixed results. Garrett et al. [41] reported higher subjective well-being among weekly visitors compared to those visiting one to two times per month. Conversely, Poulsen et al. [52] found no significant correlations between visit frequency and mental health, despite positive links to restoration and reduced perceived stress. Similarly, Aliyas [46] observed that time spent in BS positively affected general mental health outcomes, though visit frequency showed no significant effects.

Two studies explored the impact of physical activity in BS. Garrett et al. [41] and Aliyas [46] found high-intensity activities in BS significantly improved general mental health and recalled well-being among older adults.

3.5. Qualitative Evidence on Blue Space and Older Adults’ Mental Health and Well-Being

Themes extracted from qualitative studies were primarily based on interview data. Recurring environmental themes related to BS features and their potential impact on older adults’ well-being were synthesized into five primary themes. Supplementary Materials S3 provides an overview of these themes and sub-themes.

3.5.1. Natural Features

Recurring natural elements identified in the studies included water (six studies), beaches (five), wildlife (five), trees (four), climate (three), and fresh air (one). Most participants described water as a source of pleasure and emotional connection. For example, a 55-year-old participant shared a feeling of being “one with the water”, describing the experience as “intoxicating” [58]. The unique qualities of water, such as “the light on the water”, were often highlighted as magical [55]. Water was also frequently associated with therapeutic benefits, promoting calmness and healing [55,56,59]. As one 70-year-old participant noted, “I can see the water clearly… and the tide beyond goes in and out, so it’s quite therapeutic” [55] (p. 212).

Beaches, often associated with coastal BS, provided unique sensory experiences. Wildlife, especially birds [56,57] and marine life [56,58], were identified as significant features. Environments combining BS with natural vegetation (green spaces) often created restorative experiences, particularly in forest parks near lakes, rivers, or oceans [56]. An 80-year-old participant described how the unique the island’s sea and hill landscapes made “your life seem blessed” [55]. Fresh air near water bodies was also appreciated for promoting a sense of health and mental clarity [57].

Sunny and warm weather encouraged outdoor activities near BS, while cold and rainy conditions were seen as barriers [56]. However, some participants found excitement in challenging conditions, such as swimming in stormy seas during winter [58].

3.5.2. Facilities

Key facilities in BS identified by qualitative studies included trails (five studies), benches (three), artificial landscapes (two), and amenities (one). Trails or paths, in particular, played a crucial role in enabling older adults to walk and engage with the water. For instance, some participants described the enjoyment of following a winding path while admiring a water feature [55], whereas others emphasized the satisfaction they experienced when walking along a seaside trail [56]. Well-planned parks featuring interconnected pathways facilitate walking, conversation, and social interaction among older adults [59].

Benches served as essential resting spots where older adults could sit, relax, and appreciate the surrounding scenery, particularly after physical activity [59]. Additionally, artificial landscapes, including fountains [56] and gazebos [59], contributed to a sense of tranquility, provided shade, and supported social interactions among older adults. Though less frequently mentioned, amenities, such as kiosks, were recognized for their practicality and encouraging greater engagement with the environment [57].

3.5.3. Senses

All qualitative studies emphasized the unique and irreplaceable esthetic experiences provided by BS. Participants frequently noted the “lake effect” by immersing themselves and observing wildlife in natural surroundings [59]. Some shared “sit and stare” time, finding clarity and peace while gazing at the water [56].

Beyond visual esthetics, BS experiences also engaged auditory, tactile, and olfactory senses. Participants highlighted the soothing sound of flowing water [56], rustling wind, and the creaking of sail ropes [57], which fostered a sense of tranquility and pleasure. Tactile interactions, such as dipping fingers or feet into water [56] or walking barefoot on mudflats and beaches [60], deepened participants’ connection to the BS environment.

Negative sensory experiences were also noted. Some participants expressed dissatisfaction with unpleasant odors and limited water visibility from wetlands [59]. Additionally, the presence of crowds in BS can lead to negative experiences for some individuals. For instance, some participants reported avoiding the beach due to the lack of tranquility, as they found it difficult to enjoy the setting amidst the noise of people talking [57].

The natural elements within these environments evoked feelings of “being away” [55] or “hiding away” [59]. For some older adults, spending time near water could foster strong personal attachments [56,60]. However, unique BS settings, such as islands, could evoke both a sense of belonging and feelings of loneliness [55]. BS experiences were often associated with spiritual significance, such as recalling childhood memories [60] or strengthening emotional connections with deceased loved ones [56].

3.5.4. Barriers

Living near BS was linked to increased physical activity among older adults [56]. However, many encountered significant barriers that restricted their access to these environments. Older adults with limited mobility who were unable to leave their homes or visit BS often experienced social isolation and feelings of sadness [55,57]. Similarly, the distance between communities and BS, along with limited public transport, further restricted their access [55,56,57].

Safety concerns were among the key factors that restricted access for older adults. Due to the diverse types of BS, some participants were apprehensive about increased exposure to insects and ticks in wetlands [57,59]. Others avoided swimming in the ocean due to the presence of wild animals such as sharks [58] or were concerned about traffic safety while traveling to BS [57]. These perceived risks reduced their willingness to visit such environments.

In addition, cleanliness was one of the most significant challenges in maintaining BS, and the lack of cleanliness made older adults with limited mobility more concerned [56]. There were also differing opinions regarding the natural management of BS. Some participants preferred a more natural setting where they could observe wildlife, while others struggled to tolerate the presence of insects, fluctuating water levels, and unpleasant odors associated with natural environments [59].

3.5.5. Social Connections and Activities

BS enhanced social connections among older adults, primarily through social activities and intergenerational interactions. Across all qualitative studies, older adults reported that visiting BS strengthened their social relationships, particularly through interactions with friends, neighbors, and family members. BS provided a setting where older adults socialized, walked, had picnics, and watched the water [59]. These spaces also facilitated regular group activities [56]. Additionally, BS strengthened intergenerational connections, as many older adults expressed enjoyment in watching their children play or taking their grandchildren to these spaces [56,57,59,60]. These experiences significantly contributed to their overall well-being. Group activities, such as swimming, walking, cycling, and fishing, were also common [56,58,59,60], further promoting physical and mental health among older adults.

4. Discussion

4.1. Types of Blue Spaces

The range of BS examined in this review included oceans, wetlands, canals, and lakes. Most quantitative studies (n = 13) employed a macro-level approach using objective measures of outdoor BS exposure (quantity and quality), often without distinguishing between BS types. This generalized approach limited the ability to assess specific BS types and their distinct impacts on diverse populations. An emerging focus on freshwater BS was also observed in quantitative studies (n = five), all conducted in China. However, the overall number of such studies remains limited. Additionally, most qualitative studies (n = five) focused on coastal BS, with limited exploration of freshwater BS, reflecting gaps highlighted in previous reviews [25,29].

Over 50% of the global population resides within 3 km of a freshwater body [63,64]. Freshwater BS play a vital role in public health, particularly for inland populations that frequently interact with such environments. Unique ecological features of freshwater BS, including fluctuating water levels and spatial connectivity with terrestrial landscapes, can shape human experiences and well-being [65]. Future research should prioritize understanding the health impacts of freshwater BS, especially for older adults, to inform targeted urban design and public health interventions.

4.2. Challenges in Measuring Mental Health and Well-Being in Older Adults

The quantitative studies included in this review primarily rely on self-reported mental health outcomes, utilizing diverse assessment tools such as validated scales, single-item questions, and cognitive function tests. A few studies incorporated indicators like hospitalization rates or medication prescriptions. Given that health and well-being need to be assessed using multiple indicators, both objective and subjective measurement strategies are valid [66].

However, psychophysiological measures commonly used in other environmental health research were notably underutilized. Almost all of the included studies overlooked these indicators, despite their widespread application in assessing physiological responses to urban and natural environments across different age groups. Commonly employed indicators included heart rate, blood pressure, blood glucose levels, heart rate variability, skin conductance, salivary cortisol, and electroencephalography [8,67,68,69]. Since psycho-physiological responses vary with age, they are crucial for understanding how older adults interacted with their surrounding environments [70,71].

In the existing research, physiological responses were more challenging to evaluate in relation to older adults’ interaction with BS. This difficulty appeared to stem from the complexity of the biophysical mechanisms in aging populations [72], as well as interference factors in data collection and other feasibility constraints [73,74]. Additionally, the measurement tools used to assess the mental health of older adults varied significantly, complicating cross-study comparisons. Future research should expand the evidence base on the psycho-physiological effects of BS on older adults to address these gaps.

In contrast, qualitative research primarily examines the well-being of older adults, with a particular emphasis on emotional well-being, including momentary emotions, recalled well-being, and social well-being. The concept of well-being spans multiple disciplines, and much like the broader construction of health, manifests in various forms without a single definitive measure [75]. As such, qualitative methods are well-suited for an in-depth exploration of older adults’ well-being, complementing the focus of quantitative research. However, some studies have reported negative effects, possibly because individuals may respond to scenic environments in vastly different ways, experiencing them as pleasant, ambivalent, or even anxiety [76]. The interaction between individuals and natural landscapes is inherently complex and multifaceted, underscoring the highly subjective nature of blue space experiences. These variations arise from unique personal experiences and are further shaped by an individual’s broader social environment.

It is worth noting that, although limited in number, some researchers have explored the place attachment of older adults to BS. Coleman and Kearns [55] highlighted that both direct and indirect contact with island landscapes, along with various forms of interaction with BS, significantly influence elderly residents’ sense of belonging. This highlights both the diverse meanings that older adults attribute to aging and place, as well as the ways in which the material and symbolic characteristics of a place can foster well-being in later life. M. P. White et al. [20] further emphasized that the sense of pleasure and improved emotional states derived from visiting preferred places appeared to be particularly pronounced in BS environments. This phenomenon can be understood through the perspective of Peace et al. [77], who argued that as individuals grow older, they increasingly prioritize their connection to place and the role it plays in shaping their identity. Moreover, older adults affirm their identity through interactions with BS. Duedahl et al. [60] found that older adults experienced BS on a deeper level, often regarding them as favorite places imbued with personal meaning and value. Thus, place attachment can be understood as a natural bond that older adults develop with BS—serving both as a restorative element in the landscape and as a potential mechanism for enhancing their mental health and well-being.

4.3. Current Research Methodologies and Knowledge Gaps

Among the quantitative studies reviewed, the majority are cross-sectional, with only a small number of longitudinal studies and no experimental studies. Unlike experimental research, observational studies (cross-sectional and longitudinal studies) do not manipulate the environment or directly influence respondents. Instead, they provide insights into individuals’ exposure to nature within their communities and natural settings, capturing real-world interactions without external intervention. One key advantage of observational studies is their ability to assess standardized measures of psychological well-being in relation to exposure to natural environments. They offer the opportunity to examine “realistic” environmental exposures in “realistic” settings, making them more effective than experimental studies in capturing long-term impacts [78,79].

However, current research on BS largely overlooks longitudinal studies, which generally provide more comprehensive insights and stronger causal evidence than cross-sectional studies [33]. Given that natural environments, including BS, exert long-term influences on human well-being, more longitudinal studies are needed [80]. The primary limitation of cross-sectional studies is their inability to establish causality, as they can only identify associations [78]. In contrast, longitudinal studies track behavioral patterns over extended periods—often across the lifespan—and offer more robust causal evidence on a broader geographic scale [78,81].

Furthermore, experimental and quasi-experimental study designs are scientifically rigorous methods that enable researchers to investigate causal relationships in various phenomena [33]. Notably, we identified experimental studies on BS conducted in other populations. For instance, M. White et al. [82] conducted experiments to examine participants’ preferences for various water environment scenes in a laboratory setting, while Deng et al. [67] measured the restorative effects of actual water features in parks on younger adults. However, most experiments have focused on specific populations, such as university students [83,84,85], with few addressing older adults. Closing this gap could provide critical insights into how BS influences this growing demographic.

Moreover, current research on BS remains overly broad and lacks precision. The reliance on a single method for measuring spatial exposure indicators limits the clear classification of different types of BS and makes it difficult to capture the specific effects of BS characteristics on older adults. Additionally, existing studies often overlook the unique biodiversity and qualitative attributes of BS. To address these limitations, future studies should incorporate more micro-scale measurements of spatial and ecological characteristics.

4.4. Associations in Blue Space Research and Future Directions

Among the quantitative studies reviewed, the proportion of water area and proximity were the most frequently studied BS characteristics. Six studies reported positive associations between BS quantity and mental health or well-being, suggesting that older adults living in communities with more extensive BS exhibit better mental health outcomes. Similarly, five studies highlighted the positive effects of BS quality, with closer proximity linked to improved mental health. However, the diversity of BS types and buffer zone definitions contributed to heterogeneous results. Six studies found no significant relationships with BS quantity, while one reported a negative association. Regarding BS quality, three studies found no relationships, and one identified a negative relationship. Subjective assessments of BS remain underexplored, with only four studies investigating perceived quality and exposure characteristics. Among these, four found positive associations, three reported no significant relationships, and none identified negative associations. These findings highlight the heterogeneous nature of associations, with a predominance of positive correlations, some non-significant associations, and a few negative correlations. While the evidence suggests potential mental health benefits of BS for older adults, the causal relationship and the strength of this relationship remain unclear. We believe that the contradictory results observed in current studies are not only due to previously discussed factors, such as the diversity of BS types, the reliance on a single method to measure spatial exposure, and substantial variation in the mental health assessment tools used for older adults. In addition, socioeconomic factors have also emerged as key contributors to the inconsistent findings observed in BS research [9]. Variables such as gender, ethnicity, educational attainment, and broader demographic differences exert a significant influence on older adults’ likelihood of accessing BS [27,29,50]. Consequently, this relationship appears to be highly complex and shaped by a wide range of confounding variables, highlighting the need for more rigorous research.

With the few available longitudinal studies, additional studies are necessary in future research. This is important due to the fact that BS, for example, coastlines or riparian watercourses, may change with time [19,25]. The impact of BS does not occur instantaneously, so longitudinal more apt for analyzing temporal variables or events [19]. Likewise, Gascon et al. [25] call for more longitudinal Research into BS in order to better elucidate the cause-and-effect relationship between exposure to BS and human health and well-being. Thus, future research should aim at capturing longitudinal changes in exposure to BS, through approaches such as cohort studies or association analysis domestic and clinic data in order to offer more evidence for causality.

Qualitative studies provide valuable insights into how older adults perceive and experience BS, offering perspectives that quantitative methods often struggle to capture. These findings help researchers and policymakers gain deeper insights into the lived experiences of older adults in relation to BS, highlighting both its benefits and challenges. In addition, qualitative research has identified several barriers that hinder older adults’ access to and use of BS, including mobility limitations, transportation difficulties, concerns about insects and wildlife, pollution, as well as unpleasant odors and noise. It is worth noting that Duedahl et al. [60] observed that some older adults engage in pro-environmental behaviors, such as picking up litter while walking in BS. Although rarely discussed in BS research, such behaviors remain evident and traceable. Similarly, M. P. White et al. [20] noted in a review that individuals living near the coast tend to develop a stronger psychological connection to nature, which, in turn, is associated with greater engagement in environmental activities. The Blue Gym Initiative advocates for fostering a “marine mindset” that actively encourages individuals to adopt pro-marine behaviors while simultaneously enhancing their health and well-being through interactions with BS [20]. However, whether exposure to BS influences pro-environmental behavior in older adults remains unclear, highlighting the need for further research to establish stronger empirical evidence.

The findings from quantitative and qualitative research both complement and contrast each other. While quantitative studies offer evidence supporting the benefits of BS for older adults’ mental health, the lack of research on perceived quality within these studies limits direct comparisons with qualitative findings. Qualitative research offers valuable insights into the emotional and social well-being benefits that BS provide for older adults, serving as a crucial complement to quantitative studies. Therefore, future research should explore broader mixed-method approaches to establish stronger objective causal links while capturing the unique subjective experiences of well-being in older adults.

Consequently, future studies should investigate more comprehensive mixed methods for more solid objective causal relationships while conducting more detailed assessments of older adults’ unique subjective well-being experiences. Future studies should also seek to make findings more generally applicable by involving multiple geographical contexts, especially from low-income countries, where access to and use of BS could differ substantially. With population growth set greater exposure in lower- and middle-income countries [9], encompassing participants from lower socioeconomic backgrounds in these regions would provide a more thorough grasp of the health impacts and equity considerations surrounding BS. Furthermore, more emphasis should be placed upon distinguishing between varying blue spaces, including oceans, lakes, rivers and artificial water features, in order to better quantify their distinct psychological impacts. Considering such distinctions can better facilitate more directed urban planning and public health policy initiatives.

4.5. Strengths and Limitations

A key strength of this study is its in-depth analysis of the current relationship between BS and the mental health and well-being of older adults, incorporating both quantitative and qualitative evidence. This comprehensive approach allows for a detailed exploration of how BS influence mental health outcomes in this population. The quality of all included studies was evaluated based on their respective research designs. For quantitative studies, we summarized the causal relationships between various BS characteristics and different mental health and well-being outcomes. For qualitative studies, we conducted thematic analyses to provide an in-depth synthesis of BS attributes.

However, this review has several limitations. First, variations in research methodologies, characteristics measurements, and outcome assessments limit the ability to directly compare findings or perform meta-analyses. Second, the limited pool of included studies introduces a degree of subjectivity and potential bias. Third, most of the research was conducted in developed regions, particularly in Europe, North America, Oceania, and East Asia (e.g., China), which may restrict the generalizability of the findings to lower-income regions.

5. Conclusions

This systematic review synthesizes evidence on the potential benefits of BS for the mental health and well-being of older adults, incorporating insights from both quantitative and qualitative studies. Despite methodological heterogeneity, the findings collectively emphasize the significance of BS characteristics for promoting mental health and well-being. However, critical knowledge gaps remain, particularly regarding the varied impacts of different BS types and the specific needs of older adults.

As urbanization accelerates and mental health challenges among older populations increase, BS is emerging as an essential component of urban landscapes. Its potential benefits for public health have drawn attention from urban planners and healthcare professionals. Exposure to BS offers a promising strategy for improving mental health and well-being, particularly within preventive and restorative public health policies. Future research should strive to standardize measurement tools, develop comprehensive assessment frameworks, and examine the unique effects of BS on older adults’ well-being.