Metabolic syndrome (MetS) refers to a cluster of conditions (e.g., abdominal obesity, hypertension, hyperglycemia, elevated triglyceride levels, and reduced high-density lipoprotein cholesterol) that together substantially increase the risk of cardiovascular disease and type 2 diabetes (1). According to the International Diabetes Federation, the global prevalence of MetS among the general adult population is estimated to be between 20 and 25% (2). The World Health Organization also states that non-communicable conditions, including cardiovascular disease, type 2 diabetes and obesity, now account for roughly two-thirds of deaths worldwide (3). Thus, MetS represents an important public health concern.

In recent years, growing attention has been paid to the importance of health literacy in the prevention and management of MetS. Although definitions of health literacy are still evolving, one definition is “the personal skills that enable individuals to obtain, understand, and use information to make decisions and take actions that will impact their health” (4). Previous studies have consistently indicated that individuals with limited health literacy tend to have unhealthy lifestyles, poorer health self-management, and poorer health status (5–8). Thus, health literacy is closely associated with the adoption of lifestyle habits that help to prevent MetS (9).

Individuals with MetS tend to have lower levels of health literacy. Previous studies have suggested that low health literacy is associated with poor disease awareness, insufficient engagement in preventive behaviors such as engaging in physical activity and consuming a healthy diet, and deterioration of physical health status (10, 11). To address this issue, educational interventions (e.g., the distribution of informational pamphlets and verbal counseling) targeting individuals with MetS have been implemented. Previous reports have indicated improvements in clinical indicators such as body weight, waist circumference, and body mass index following lifestyle guidance (12, 13). However, such interventions targeting individuals with MetS are often influenced by individual factors such as receptiveness, motivation, and environmental conditions. Thus, the effectiveness of interventions in sustaining long-term behavioral change and disease management remains limited.

Individuals with MetS are influenced by their family members. Previous research has shown that emotional and practical support from family members—particularly spouses—can contribute to improved dietary and drinking habits, as well as to better clinical outcomes such as improved blood pressure, blood glucose, and lipid levels. (14–16). A previous report also suggested that family members’ knowledge about nutrition and physical activity may promote improvement in the patient’s own lifestyle (17).

Given these findings, family members’ health literacy may influence preventive behaviors and disease management in individuals with MetS. However, no studies to date have assessed health literacy among family members of individuals with MetS. Thus, it is unknown whether lifestyle habits in patients with MetS are associated with the health literacy of their family members. In this study, we aimed to examine the associations between lifestyle habits (dietary habits, exercise, alcohol consumption, and smoking) among individuals with MetS and the health literacy of their family members. The findings are expected to highlight the need for comprehensive support systems that include family involvement, as well as the importance of providing health education targeting family members. This study may contribute to the development of more effective and sustainable support models for the improvement of lifestyles among individuals with MetS.

Table 1 shows the characteristics and health literacy scores for participants and their family members. A total of 116 (92.8%) participants were men, 62 (49.6%) were in their 40s, 105 (84.0%) were married, and 109 (87.2%) were not shift workers. In 100 participants (80.0%), the family member who completed the survey was the participant’s spouse. The mean participant and family member health literacy scores were 3.58 (standard deviation [SD] 0.71) and 3.52 (SD 0.70). Table 2 shows the bivariate association between participants’ and family members’ health literacy. The health literacy score for family members was positively correlated with the health literacy score of participants (r = 0.384, p < 0.001). Table 3 shows the univariate associations between participants’ lifestyle habits and participants’ and family members’ health literacy. Among participants, 46 (37.1%) ate dinner at least 2 h before bedtime at least 3 times a week, 38 (30.6%) performed walking or equivalent physical activity each day for at least 1 h daily, and 43 (34.4%) were smokers. We found univariate associations between participants’ health literacy and participants’ exercise habits (moderate exercise and walking or equivalent physical activity). We also found univariate associations between family members’ health literacy and participants’ dietary habits (time dinner is eaten), exercise habits (moderate exercise, walking or equivalent physical activity), and smoking status. Table 4 shows the results of binary logistic regression analysis. After adjusting for seven variables related to sociodemographic factors and occupation and workplace factors, we found that participants’ exercise habits (moderate exercise, walking or equivalent physical activity) were significantly associated with participants’ health literacy (OR = 4.654, p < 0.001 and OR = 2.689, p = 0.001, respectively) (Model 1). Additionally, we found that participants’ dietary habits (dinner time) and exercise habits (moderate exercise) were independently associated with family members’ health literacy (OR = 2.485, p = 0.006 and OR = 2.819, p = 0.034, respectively) (Model 2).

In this study, we examined the associations of lifestyle habits among MetS in middle-aged adults and their family members’ health literacy. Compared with the results of specific health checkups conducted for all Japanese citizens aged 40 years and older, the participants in this study had lower rates of skipping breakfast 3 or more times a week, eating dinner at least 2 h before bedtime at least 3 times a week, engaging in moderate exercise, and engaging in walking or equivalent activity each day for at least 1 h daily (22). The mean health literacy scores among participants’ family members were 3.52 (SD 0.70). This score is comparable to the findings of a previous study conducted among 501 pairs of Japanese residents aged 30–79 years and family members with whom participants most often consulted for help with health issues (mean ± SD 3.50 ± 0.77) (23). The health literacy score of family members was positively correlated with participants’ health literacy score. This finding is consistent with those of a previous study that identified a close correlation of family members’ health literacy with participants’ health literacy (23). In the present study, family members’ health literacy was independently associated with participants’ dietary habits (time dinner is eaten) and exercise habits (moderate exercise).

Our study participants who lived in the same household as family members who had better health literacy tended to eat dinner at least 2 h before bedtime, at least 3 times a week, as compared with those whose family members had poorer health literacy. According to a survey conducted by the Statistics Bureau of the Ministry of Internal Affairs and Communications, married Japanese women spend 14.6 times more time managing meals than husbands (24), and it has been reported that many employed women in Japan are responsible for meal management (25). In our study, 80.0% of participants reported that their cohabiting spouse was the person most concerned about their health, and 92.8% of the participants were men. Thus, it is possible that many of our participants were married men living with their wives and that they typically consumed dinners prepared by their spouse. Thus, participants who lived with family members—particularly wives—who had high health literacy may have had dinner served and consumed at appropriate times, regardless of their own level of health literacy. In general, eating dinner close to bedtime is associated with lifestyle-related diseases, including MetS (26). Enhancing the health literacy of family members may reduce the risk of worsening metabolic syndrome and associated cardiovascular diseases among individuals with MetS through optimization of their mealtimes.

Our study participants who lived in the same household as family members with better health literacy tended to engage in moderate physical activity, as compared with those whose family members had poorer health literacy. Previous studies have suggested that family support is a predictive factor of exercise adherence (27) and is associated with persistent or increasing physical activity (28). Previous studies have revealed that individuals benefit from the “distributed nature” of health literacy through shared knowledge, supported skills and practices, supported behaviors, and supported decision-making provided by health literacy mediators belonging to their social networks (23, 29). Thus, participants who lived with family members who had high health literacy may have been more likely to engage in physical activity, as they were more likely to receive support for decision-making and adherence related to exercise from their family members.

This study has several limitations. First, because this was a cross-sectional observational study, we were unable to determine causal relationships among the determinants of participants’ lifestyle habits. Second, participants were recruited from only one company. Additionally, our study population was limited to those over 40 years of age. The generalizability of our findings should be approached with caution based on these sample characteristics. Third, contrary to previous reports measuring functional health literacy, we assessed interactive and critical health literacy. The mean participant health literacy score was 3.58 (SD 0.71), which is lower than that found in a study of Japanese office workers (N = 190; mean ± SD 3.72 ± 0.68) (21). The scores obtained in this study were also lower than those in a nationwide online survey of the general Japanese population, which included older adults (N = 712; mean ± SD 3.59 ± 0.62) (30). Fewer participants in the present study may have had sufficient health literacy to engage in behaviors to protect their health; thus, participants’ lifestyle may have been more easily influenced by their family members’ health literacy. Fourth, most participants in this study were men. Thus, the findings may have differed if the study population included more female participants. Future research should include women to evaluate potential sex-based differences.

Despite the above limitations, we explored the associations between lifestyle habits among middle-aged adults with MetS and their family members’ health literacy. In our study, participants’ dietary habits (time dinner was eaten) and exercise habits (moderate exercise) were independently associated with their family members’ health literacy. Our results indicate that health education for individuals with MetS as well as their family members may be effective in improving dietary and exercise habits among individuals with MetS themselves. To address the development of sustainable support models for individuals with MetS, further research is needed to examine the effects of family health education on individuals’ improvement in lifestyles habits.