1. Introduction
Personality reflects individual differences in relatively enduring patterns of thoughts, feelings, and behaviors. There is a general consensus that the big five personality traits represent the most basic adult personality factors [
1]. These five traits, which indicate patterns and trends, are the following: neuroticism (being emotionally unstable and experiencing negative emotions); extraversion (being assertive and social, experiencing positive affect, and seeking excitement); openness (being creative, curious, sensitive to aesthetics, and open to new ideas and experiences); agreeableness (being altruistic, trusting, modest, and compliant); and conscientiousness (being persistent, organized, and goal-directed, and showing self-control and self-discipline) [
1,
2]. Personality traits have been associated with subjective well-being, health, and mortality risk during aging [
3,
4,
5]. In addition, some authors have suggested that the link between personality traits and health may be cumulative over time, and, therefore, personality could have a greater influence on disease in old age [
5].
Personality has been considered a risk factor for metabolic syndrome (MetS) [
6], whose prevalence rises with age [
7] and increases the risk of cardiovascular outcomes and all-cause mortality [
8]. According to the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III), MetS is diagnosed when an individual has three or more risk factors, including high waist-circumference (WC), high blood pressure, high triglycerides (TGL) and low high-density lipoprotein cholesterol levels (HDL-cholesterol), and high glucose [
9]. Sutin et al. [
10,
11] analyzed the relationship between the big five personality traits and metabolic health, and they concluded that the association between neuroticism and conscientiousness and metabolic dysfunction starts early, whereas the association with agreeableness emerges at older ages, suggesting that this association may unfold across the lifespan [
11]. Furthermore, they observed that gender moderated the associations between impulsiveness (a facet of neuroticism), openness, and MetS [
10]. Therefore, these results suggest an association between some personality traits and MetS in older adults, as well as gender differences in these associations.
Personality has also been related to subjective health (also called self-assessed health, or health-related quality of life [HRQoL]), and this association appears to be more pronounced with age [
12]. In older adults, subjective health has been associated with health-literacy, self-efficacy, physical health-promoting behavior, perceived emotional-informational support [
13], and health outcomes and mortality [
14]. Subjective health has been widely assessed with the Short Form Health Survey (SF-36), which contains eight subscales that can be grouped into the two main components, subjective physical and mental health [
15]. In studies that analyzed the association between personality traits and the subjective-physical health scale or some subscale components, higher neuroticism was related to worse subjective-physical health in most studies [
4,
12,
16,
17,
18], but not in all of them [
19,
20]. Similarly, higher extraversion [
4,
12,
16,
17,
20] and conscientiousness [
16,
17,
18,
19,
20] were related to better subjective-physical health in most studies. In contrast, openness [
4,
12,
20] and agreeableness [
4] were associated with subjective-physical health subscales in a few studies. In addition, only Jerram and Coleman [
4] analyzed these associations separately in men and women, and they suggested that the results for the whole sample were a poor reflection of the results for men and women separately. Therefore, the study of the moderating effect of gender is a pending issue.
Although objective health is usually positively associated with subjective health, subjective health cannot be considered a simple reflection of physical health. In addition, this association tends to be weaker with age. Older adults may modify their criteria for perceived health to emphasize deteriorations in physical health, and they are more likely to base their physical health on attitudes (i.e., a positive outlook on life) and behaviors (i.e., a healthy lifestyle) [
21]. A recent study observed that personality moderated the association between objective (including clinical [MetS risk factors: hypertension, glucose and Glycated Hemoglobin (HbA1c)], motor and cognitive status) and subjective (measured with a single item) health in older adults with type 2 diabetes [
22]. Elran-Barak, Weinstein, Beeri, and Ravona-Springer [
22] observed that objective–subjective health associations were stronger in individuals with an “unfavorable” personality, specifically those with high neuroticism and low openness and agreeableness. Moreover, regarding the MetS components, they reported that the association between hypertension and subjective health was only observed in individuals with high neuroticism [
22]. The role of personality in the association between objective (MetS) and subjective health has hardly been analyzed in older adults. Moreover, some studies suggest that the association between MetS and subjective health is only observed in women [
23].
Hence, the present study aimed to analyze the relationships between the personality traits and both objective (MetS) and subjective-physical health in older people, as well as gender differences in these relationships. In addition, we aimed to examine the moderating role of personality and gender in the association between objective and subjective-physical health. We hypothesized that individuals with higher neuroticism and lower conscientiousness and agreeableness would be more likely to have MetS [
10]. We also hypothesized that higher neuroticism and lower conscientiousness would be related to lower subjective-physical health [
18]. Finally, we expected neuroticism to moderate the association between MetS and subjective-physical health, and so a negative association would be observed when neuroticism is high [
22]. Because gender differences in these associations have seldom been explored, we did not formulate specific hypotheses.
2. Materials and Methods
2.1. Participants
One-hundred and thirty-eight participants (64 men and 74 women), ranging in age from 56 to 80 years (M = 66.85, SD = 4.97), were recruited from a study program at the University of Valencia (Spain) for people over 55 years old. This study is part of the MNEME Project, a large research project designed to explore the relationships among cognitive functioning and psychological and physiological factors, including hypothalamic–pituitary–adrenal axis functioning, in older people. Exclusion criteria for this research were: smoking more than 10 cigarettes a day, alcohol or other drug abuse, diabetes, or severe psychiatric or endocrine diseases. All the women were postmenopausal, and none of them were receiving hormone replacement therapy. None of the participants scored less than 27 on the Spanish version of the Mini-Mental Status Examination [
24], indicating the absence of cognitive impairment. Of the total sample, the five MetS risk factors were obtained from only 98 participants, who were categorized according to the presence or absence of MetS (see
Section 2.4).
2.2. Procedure
The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Research Ethics Committee of the University of Valencia (Principal Investigator: Prof. Dr. Alicia Salvador). All participants provided written informed consent.
Participants were asked to attend one session that took place at 10:00 or 12:00 h in the Laboratory of Social Cognitive Neuroscience at the University of Valencia. Once in the laboratory, participants filled out the questionnaires to measure their personality traits and subjective-physical health (see
Section 2.3 and
Section 2.5). In addition, WC, blood pressure, TGL, HDL-cholesterol, and HbA1c were measured to assess MetS. Participants were also asked for their educational level and current degree of physical activity. To do so, participants had to check one of the following options: (i) “Avoid walking or getting tired. Always use the elevator and means of transport” (avoid physical activity); (ii) “Walk for pleasure, use the stairs. Occasionally do exercises that cause sweating or fast breathing” (light physical activity); (iii) “regularly participate in physical activities that require moderate efforts such as maintenance gymnastics, biking, walking, dancing, yoga, golf, ping-pong, horseback riding, or similar activities” (moderate physical activity); or (iv) “regularly participate in vigorous physical activities, such as running, swimming, brisk walking, rowing, cycling, playing tennis, basketball, or similar activities” (vigorous physical activity).
2.3. Personality Traits
The Spanish version [
25] of the NEO Five Factor Inventory (NEO-FFI) [
1] was used to measure the personality traits. The NEO-FFI consists of 60 items that measure the big five personality traits (neuroticism, extraversion, openness, agreeableness, and conscientiousness), with 12 items for each. The items are answered on 5-point scales, and higher scores indicate a higher degree of the trait. The internal reliabilities for the subscales in the present study were good, with Cronbach’s alphas of 0.81 (neuroticism), 0.84 (extraversion), 0.66 (openness), 0.73 (agreeableness), and 0.83 (conscientiousness).
2.4. Objective Health: MetS
WC (cm) was measured to assess central adiposity. Blood pressure (mm Hg) was assessed using the ORMON M6W automatic blood pressure monitor (ORMON Healthcare, Kyoto, Japan). Participants were in a seated position, and three measures were taken at 30-s intervals and averaged. TGL, HDL-cholesterol, and HbA1c were assessed from capillary blood samples with the Cobas b 101 system (Roche Diagnostics, Barcelona, Spain). In addition, participants reported whether they took medication for hypertension or dyslipidemia.
MetS was defined as the presence of three or more of the following risk factors: (1) elevated WC (≥102 cm in men and ≥88 cm in women), (2) elevated blood pressure (≥130 mmHg systolic blood pressure, ≥85 mmHg diastolic blood pressure, or on antihypertensive drug treatment), (3) elevated TGL (≥150 mg/dL or drug treatment for elevated TGL), (4) reduced HDL-cholesterol (<40 mg/dL in men and <50 mg/dL in women, or drug treatment for reduced HDL-cholesterol), and (5) elevated HbA1c (≥5.7%). We followed the guidelines from the US NCEP-ATP III [
9], except for the hyperglycemia risk factor, which is defined as elevated fasting glucose ≥100 mmol/L, which corresponds to a prediabetes condition. Because we did not obtain fasting glucose, we considered ≥5.7% HbA1c, which is the cut-point for prediabetes [
26], to identify the hyperglycemia risk factor. Participants who showed 3 or more risk factors were given a score of 1 on the category of presence of MetS, and the rest were given a score of 0.
2.5. Subjective-Physical Health
The Spanish version [
27] of the Short Form Health Survey (SF-36) [
15] was administered to measure subjective health. It consists of 36 items distributed in eight subscales: physical functioning (PF), role-physical (RF), bodily pain (BP), general health (GH), vitality (V), social functioning (SF), role-emotional (RE), and mental health (MH). For each subscale, the items were transformed into a scale ranging from 0 (worst health) to 100 (best health), using the algorithms and instructions provided in the manual. The eight subscales can be grouped in two summary measures: physical health (PF, RF, BP, GH, and V) and mental health (GH, V, SF, RE, and MH) scales. Based on the aims of the present study, we only employed the physical health scale, which had a Cronbach’s α = 0.71.
2.6. Statistical Analysis
Participants’ characteristics were described using descriptive statistic tools (means, standard deviations, (SD) or percentages) when appropriate, for the total sample and for men and women independently. To investigate gender differences in age, personality traits, and subjective-physical health, independent sample Student-t tests were performed. Pearson’s Chi-square test was used to assess gender differences in the educational level, physical activity, and MetS.
To investigate whether personality traits were associated with MetS adjusted for covariates (age, gender, educational level, and physical activity), logistic regression analysis was performed, including MetS as dependent variable, the covariates in block one, and the personality traits in block two. Then, to determine the relationships between personality traits and subjective-physical health, we performed hierarchical regression analysis, including subjective-physical health as the dependent variable, the covariates in block one, and the personality traits in block two. After that, to analyze the association between MetS and subjective-physical health, we again performed hierarchical regression analysis, including subjective-physical health as the dependent variable, the covariates in block one, and the MetS in block two. Finally, we analyzed whether gender or personality traits moderated these relationships, using the PROCESS macro in SPSS (v3.4) (Model 1) with 5000 bootstrapped samples.
Data on NEO-FFI were obtained for the entire sample (N = 138), but there was one missing value for SF-36 (N = 137), and the five MetS risk factors were available for only 98 participants, as mentioned above. Moreover, five multivariate outliers were detected with standardized residuals (±3 SD) and excluded from the analyses. Therefore, the number of participants varied in the different analyses.
To perform these statistical analyses, version 25.0 of SPSS was used. All p values were two-tailed, and the level of significance was taken as p < 0.05.