The creation of an aging society is accelerating due to the developments in medicine, and an increase in chronic diseases, such as cardiovascular diseases, diabetes, and cancer is emerging as a serious social problem. The prevalence of these chronic diseases increases with age, and it was found that 89.5% of the elderly population aged 65 years and over suffered from at least one chronic disease in Korea [1].

Hypertension is one of the most common chronic diseases of the cardiovascular system and is a major cause of diseases, such as coronary artery disease, stroke, and renal failure [2,3]. In Korea, approximately 30% of adults aged 30 years and older suffer from hypertension, indicating a high prevalence of chronic diseases [4]. The risk factors for hypertension include weight gain, unhealthy eating habits, excessive sodium intake, lack of physical activity, and excessive alcohol intake [5]. In particular, hypertension is closely related to weight gain, and a high obesity index, such as body mass index (BMI), waist circumference, and body fat percentage increases the prevalence of hypertension [6-9].

Muscles play an important role in the energy metabolism of the body and are highly correlated with metabolic diseases, such as obesity, diabetes, and metabolic syndrome [10-12]. In addition, muscle strength is mainly used as a risk predictor of metabolic diseases because it reflects not only the muscle mass but also the level of physical activity [13,14]. Sarcopenia occurs due to the deterioration of muscle function, structure, and activity as aging progresses in the elderly, and muscles decrease by ~8% for 10 years from the age of 40 years, and ~15% for 10 years from the age of 70 years [15]. Sarcopenia and muscle weakness are expected to be closely associated with the high prevalence of hypertension in the elderly. According to a study that analyzed the correlation between BMI, muscle mass, and blood pressure (BP) in 121 elderly men with borderline hypertension in Korea, if the BMI was > 25 kg/m² or the muscle mass decreased, hypertension was likely to develop [16]. In addition, a study investigating the relationship between hand grip strength (HGS) and hypertension in adults and the elderly using large-scale data from the National Health and Nutrition Examination Survey showed that the prevalence of hypertension was lower when the HGS was high [17,18].

HGS is mainly used as a simple, convenient, and economical tool to evaluate muscle strength; it is known that when measuring HGS in an upright posture, the force of the lower body and core muscles is reflected [19]. Since HGS is closely related to weight, it is recommended to use relative HGS (RHGS) obtained by dividing the grip strength by body weight [20]. Recent studies investigating the relationship between RHGS and chronic diseases, such as metabolic syndrome and diabetes, are being conducted continuously [12,21,22].

Although previous studies investigated the effects of muscle strength and obesity indicators, such as BMI and waist circumference, on hypertension, they have only investigated individual correlations with each indicator. In addition, few studies have examined the relationship between BMI, RHGS, and hypertension in the elderly. Furthermore, for HGS, it would be difficult to draw a result completely excluding the effect of body weight, since most of the studies used absolute HGS rather than RHGS. Therefore, the purpose of this study was to analyze the association between the prevalence of hypertension, BMI, and RHGS among elderly individuals in Korea.

This study was conducted to investigate the relationship between the prevalence of hypertension, BMI, and RHGS in the elderly using data from the 2019 National Physical Fitness Survey. The results showed that elderly men and women with high BMI, and elderly men with weak RHGS were more likely to have hypertension.

The results of this study suggest that weight management is important for the prevention and management of hypertension in the elderly. BMI is the most commonly used index in the field of clinical practice and can be calculated easily using weight and height [16]. Since it has also been used in several previous studies, it has the advantage of being easy to compare among countries by age group. Although BMI has a limitation in that it may not clearly reflect the body fat mass component, it has a high correlation with the percentage of muscle mass [24], and is often used as an indicator of obesity in clinical practice due to its high level of association with the risk of metabolic diseases. The results of the study showed that the elderly who were overweight or obese had a higher age, height, weight, BMI, body fat percentage, SBP, DBP, and HGS compared to the elderly with normal-weight. According to a previous study on the differences and correlation of body composition and functional fitness in the elderly population, the body composition and functional fitness of the elderly were weakened with increasing age, and their SBP and DBP increased with increasing BMI and waist circumference [25]. In addition, a previous study that analyzed the risk factors for hypertension in the elderly aged 65 years or older reported that the prevalence of hypertension was found to increase when the BMI was high or diabetes was diagnosed [26]. Indeed, hypertension is an aging-related chronic disease; thus, the management of risk factors—weight and muscle strength—is important to prevent and manage hypertension in the elderly.

In particular, according to the results of this study, the absolute HGS was high in the overweight and obese groups; however, the RHGS was low, suggesting that the absolute HGS can be greatly affected by body weight. RHGS is a value obtained by dividing the HGS by the body weight. Even if the HGS value is similar, the RHGS is estimated to be low if the body weight is high. Therefore, RHGS should be used as a predictor of hypertension rather than absolute HGS.

In this study, the group with weak RHGS was more likely to have hypertension than the group with strong RHGS in men, while there was no significant difference in women. The analysis of the percentage of hypertension according to the RHGS groups revealed that 41.4% of the strong RHGS group, 46.3% of the middle RHGS group, and 43.7% of the weak RHGS group were found to have hypertension. In women, 31.8% of the strong RHGS group, 33.4% of the middle RHGS group, and 33.7% of the weak RHGS group were found to have hypertension. In both groups, the weak RHGS group was more likely to have hypertension compared to the other two RHGS groups; however, in the case of women, the difference in the percentage of patients with hypertension between the RHGS groups was rather small, and no statistically significant results were obtained.

According to previous studies, HGS has been a factor in predicting hypertension because it reflects exercise participation as well as muscle strength. Lee [17] reported that the average number of days of high-intensity exercise, strength exercise, and flexibility exercise in participants with high HGS was more than 3 days. Furthermore, HGS exercise has a positive effect on BP reduction. According to a literature review on HGS exercise, it was reported that grip strength exercise intervention was effective in lowering SBP up to 13 mmHg or more and DBP up to 8 mmHg or more [27].

According to statistics of the elderly provided by Statistics Korea, 15.7% of the population aged 65 years and above in Korea in 2020 is expected to become a super-aged society of 20.3% by 2025 [28]. Improving the health of the elderly is considered a very important issue for improving the quality of life of individuals and reducing social costs, including medical expenses. Once hypertension occurs, continuous management is required, which is a major cause of increased medical expenses for the elderly and increased burden on their dependents. Because hypertension is a cause of cardiovascular disease that can lead to serious sequelae or death, prevention and management of hypertension are essential for the elderly. Therefore, longitudinal studies to clearly identify and follow up risk factors for hypertension should be conducted to prevent hypertension in the elderly and to maintain a national management system to prevent secondary diseases.

This study has several limitations. First, there may be selection bias as the elderly individuals selected as participants in this study were limited to those whose body composition and physical strength were measured in 2019. In addition, we could not determine whether the participants were taking antihypertensive drugs. As BP was lowered when taking antihypertensive drugs, the measured value would be lower than the criteria for determining hypertension in this study; therefore, it may not be classified as hypertension. Thus, further studies should investigate whether antihypertensive drugs are being taken or not. Finally, demographic characteristics, such as education, income level, and occupation were not sufficiently reflected in this study. Since chronic diseases, such as hypertension are closely related to these socioeconomic factors, a study to analyze the risk factors for hypertension according to factors, such as education level, income level, and occupation should be conducted.

In conclusion, this study confirmed that weight management is necessary for the prevention and management of hypertension in the elderly. Furthermore, RHGS, which reflects weight, was also identified as a predictor of hypertension in elderly men.