**1. Introduction**

The prevalence of hypertension has more than doubled in the last 30 years, making it one of the leading causes of disease and mortality worldwide, with an estimated 1.28 billion people suffering from hypertension in 2019 [1,2]. Hypertension has become one of the leading causes of death in Japan among noncommunicable diseases [3,4]. Alarmingly, the number of people with hypertension in Japan is estimated to be 43 million [1,5], but only

**Citation:** Marito, P.; Hasegawa, Y.; Tamaki, K.; Sta. Maria, M.T.;

Yoshimoto, T.; Kusunoki, H.; Tsuji, S.; Wada, Y.; Ono, T.; Sawada, T.; et al. The Association of Dietary Intake, Oral Health, and Blood Pressure in Older Adults: A Cross-Sectional Observational Study. *Nutrients* **2022**, *14*, 1279. https://doi.org/10.3390/ nu14061279

Academic Editors: Abeer M. Mahmoud and Shane Phillips

Received: 4 February 2022 Accepted: 14 March 2022 Published: 17 March 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

50% received treatment, while 25% had controlled blood pressure (BP) [5]. Furthermore, approximately 70% of older adult population (≥75 years) of Japan has hypertension [6]. According to the Japan Society of Hypertension, individuals who are ≥ 75 years old with a BP ≥ 140/90 mmHg are considered hypertensive [5]. Hypertension is a complex medical condition caused by several factors. Previous studies have identified that periodontal disease [7], occlusal status [8], and tooth loss [8–10] are associated with hypertension. However, the role of oral health in hypertension is yet to be clarified. Identifying the risk factors for hypertension, even those with marginal risk, is crucial to devise strategies to prevent the development of hypertension and thus prevent cardiovascular disease. Several studies have reported that hypertension is associated with oral health, including impaired mastication, poor oral hygiene, and oral inflammation [7,9–11].

Oral health, which is an indicator of general health, can be affected by a range of diseases and conditions that include dental caries, periodontal disease, and tooth loss [12]. Teeth and oral function constitute the main pathways considered vital in connecting oral to general health. According to the Health 21 plan of Japan, improvement of oral function is the primary target for older adults [13], and the number of teeth has been long established as one of the indicators of the oral health condition [14]. According to the Japan Dental Diseases Survey in 2016, approximately 280,000 and 100,000 patients were estimated to have minor (1–8 missing teeth in one jaw) and major (9–14 missing teeth in one jaw) tooth loss, respectively [15]. Further, adults (≥75 years) lose a minimum of ten teeth per year [16]. A study has reported that tooth loss, particularly in older adults, was associated with malnutrition [17]. Tooth loss invariably leads to the decline of mastication ability, changes in food selection and dietary intake, and changes in nutrient intake, all of which, consequently, have an adverse effect on general health, increasing the risk of systemic diseases, frailty, and mortality [17–22].

As oral and general health decline with aging and disease(s) [20,21,23–26], the number of unchewable food particles increases over time, leading to changes in food selection and eating habits [19,23,24]. According to the 2018 National Health Nutrition Survey in Japan, approximately 25% of people (≥60 years of age) reported a decline in masticatory function, which implies that they were unable to chew a variety of food [13]. Mastication is the first step of the digestive process of breaking food into smaller particles for swallowing that allows more nutrient absorption, which is essential for the maintenance of health, especially in older adults [24,27]. Numerous studies have reported that masticatory function is influenced by several factors, such as the number of remaining teeth [21,28], posterior occlusal contact [21,29,30], occlusal force [21,30], salivary secretion [28,30], and tongue function [28,31]. Tooth loss influences an individual's food choice and dietary intake, leading to maladaptive behaviors. For example, an individual with tooth loss will prefer eating soft and easy-to-chew foods [32], and will avoid fiber-rich and nutrient-dense foods, such as raw fruits and vegetables, nuts, meats, and grain products, thereby increasing fat, sugar, other carbohydrates, and processed food consumption [32,33].

To measure an individual s usual food consumption and dietary intake, a food frequency questionnaire can be utilized. Food questionnaires have become one of the main research tools in nutritional epidemiology [34]. In Japan, Sasaki et al. [35] developed a brief self-administered diet history questionnaire (BDHQ) to assess the Japanese diet, which uses food frequency and dietary history. The BDHQ is a validated food frequency questionnaire that estimates the dietary intake of 58 food and beverage items during the preceding month. It consists of the following five sections: intake frequency of food and non-alcoholic beverages, daily intake of rice and miso soup, frequency of drinking alcoholic beverages and amount per drink for five alcoholic beverages, usual cooking methods, and general dietary behaviors [35–37]. The food and beverage items included in the questionnaire were mainly from a food list used in Japan s National Health and Nutrition Survey, which is based on foods commonly consumed in Japan [35].

It is widely established that there are relationships between nutrition and hypertension [38–40], and between oral health and hypertension [7–10,41]. A study by Fushida

et al. [41] elucidated the link between high BP and decreased masticatory performance; however, their study did not assess the role of oral health in nutrition. As stated by the authors, a non-direct causal relationship was assumed between high BP and decreased masticatory ability [41]. Nutritional status is expected to be very strongly associated with the relationship between high BP and decreased masticatory performance, among several other expected confounding factors [8,41]. Therefore, the authors felt the need to investigate further the association of oral health with hypertension, indirectly, by assessing nutrition, to better understand the cardiovascular demographics in older adults.

The authors hypothesized that impaired oral health can cause nutritional imbalances, which might affect blood pressure. Hence, in this study, we aimed to investigate the dietary intake of the Japanese older adult population to clarify the role of oral health in nutrition and hypertension.
