During the past decades, the rapid development of economic growth, changes in lifestyle, and longer life expectancy have led to an increase in the geriatric population worldwide. According to the Seventh National Population Census in 2020, the share of the population aged above 60 and 65 years increased by 5.44% (from 13.26% in 2010 to 18.70% in 2020) and 4.6% (from 8.9 to 13.5%) in past 10 years, respectively (1). The percentage of subjects aged 60 and 65 years and above in rural China was 23.8 and 17.7%, which is 7.99%, and 6.61% higher than those in urban areas, respectively (1). Age-related metabolic disorders, such as hypertension, diabetes, obesity, and dyslipidemia, gradually became more prevalent in this aging population. A Korean cardiometabolic syndrome survey reported an increasing case of metabolic syndrome with an increase in age, with the highest rate among subjects older than 60 (37.9%) (2). The National Survey of Health, Wellbeing, and Aging survey also showed that the prevalence of MetS was 66.0% in older women and 47.1% in older men (3–5) and is relatively more prevalent among urban than rural residents (6, 7). However, data from our study indicated that the prevalence of MetS among general rural residents was 39.0%, which was significantly higher than many other rural Chinese areas, such as Hanzhong (15.1%), Nantong (23.3%), and Xinjiang (14.43%) (8–10). The elderly population with MetS consisted of a large proportion of those in rural areas. It is well-established how metabolic disorders significantly correlate with cardiovascular events (CVEs), cancer, psoriasis, erectile dysfunction, osteoporosis, and many other non-communicable diseases (11–13). Moreover, the prognosis of dyslipidemia correlated with increased atherosclerotic extension in prediabetic and newly diagnosed patients with type 2 diabetes (T2D) (14). Studies showed how obesity has increased the risk of coronary and peripheral atherosclerotic burden (15). In addition, hyperglycemia has been reported to be associated with a higher coronary and peripheral atherosclerotic burden in patients with non-diabetes (16). In summary, MetS has led to an increased incidence of cardiovascular disease, coronary heart disease, and stroke (13, 17, 18). This observation warrants the identification of the possible predictors of cardiovascular events (CVEs) in rural elderly patients with MetS to develop effective preventive strategies. Cardiovascular diseases (CVD) have become the primary cause of mortality among elderly patients in recent years. However, the improvement in prevention, diagnosis, and treatment of cardiovascular risk factors induced a fall in CVD-mediated mortality in developed countries (19, 20). Nevertheless, the gradual prevalence of metabolic disorders such as obesity, hypertension, diabetes, and dyslipidemia in rural China synchronously increased CVD mortality (21, 22). Most previous studies to estimate the possible risk factors of MetS in rural China had cross-sectional designs, leading to less convincing conclusions. Therefore, in this study, we aimed to identify the potential risk factors of newly diagnosed MetS among rural elderly residents and determine if gender-related differences affected the prognosis.

The present study identified an increase in SBP by 1 mmHg, a family history of stroke, a soybean and soybean product consumption rate of 2–3 times/week, and alcohol consumption habits as crucial predictors of CVEs in both genders with MetS. In addition, Han Chinese's race descendancy, family history of hypertension, high levels of LDL-C, uric acid, and hemoglobin, an income range of 5,000–20,000 CNY/year, and heavy physical activity were specific predictors of CVEs among male elderly patients but not among female patients with MetS at baseline. BMI and FPG were risk factors for both genders, considering the associated factors of newly diagnosed MetS. Our analyses identified >9 h/day of sleep as a protective and LDL-C as a risk factor for newly diagnosed MetS among female elderly patients. In contrast, age and SBP were associated factors in elderly male patients but not in female patients.

One study including 6,828 adult patients with MetS concluded that factors such as the male gender, age, cigarette smoking, meat/food intake, dietary pattern, and metabolic components at the baseline significantly positively affected the risk of developing MetS (28). Hence, they suggested abstaining from cigarette smoking and dietary pattern modification as the major prevention strategies for controlling MetS. Another study showed that an intermediate level of physical activity seemed to be a protective factor for MetS (29), suggesting a need for MetS prevention strategies that promote physical activity. However, a study specifically comprising elderly patients found no difference in physical activity between older adults with MetS and those without this diagnosis (30). We corroborated this result by finding no statistically significant relationship between physical activity and newly diagnosed MetS among rural elderly patients. A possible reason behind such an observation might be the relatively low rate of moderate and heavy physical activity among older subjects due to aging. In our study, BMI and FPG at baseline were identified as common risk factors for newly diagnosed MetS in both genders, which is consistent with observations already corroborated by previous studies. SoMi Park and colleagues reported that the risk groups of metabolic indicators all showed statistically significant differences according to BMI. The percentage of subjects with abnormal findings for all indicators significantly increased with an increase in BMI (31). Moreover, female elderly patients possessed a relatively higher risk of developing MetS than male elderly patients, warranting more attention except for the common risk factors of newly diagnosed MetS in both genders. LDL-C and smoking habits were also risk factors for MetS in female elderly patients. Cigarette smoking significantly positively affects the risk of developing MetS (28). As previously emphasized, elderly patients must pay attention to their blood lipid profile, glucose, and blood pressure and monitor them frequently to discover abnormal changes as early as possible. In recent years, cumulative evidence emphasized the beneficial effects of a decrease in the levels of lipid, glucose, and antihypertensive medication on cardiovascular diseases (32–34). However, data from the DYSIS-China study reported that attaining the goals for lowering both LDL-C and non-HDL-C occurred less frequently in MetS Chinese than in those without MetS, which underscored the necessity of adding recommendations about strategies for controlling multiple risk factors to decrease the risk related to dyslipidemia in MetS subjects in future guidelines (35). In our study, >9 h/day of sleep duration was associated with a lower risk of MetS in female elderly patients. A systemic review claimed that shorter sleep durations were significantly associated with a higher prevalence of MetS (OR = 1.11, 95% CI = 1.05–1.18) and incident MetS (RR = 1.28, 95% CI = 1.07–1.53) in cross-sectional and longitudinal studies, respectively. However, long sleep duration was significantly associated with an increased prevalence of MetS in cross-sectional studies (OR = 1.14, 95% CI = 1.05–1.23) but not with the incidences of MetS (RR = 1.16, 95% CI = 0.95–1.41) in longitudinal studies (36). Furthermore, other reviews highlighted a U-shaped association between sleep duration and MetS. It has been reported that short and long sleep durations are associated with a higher risk of MetS in women (37). Future studies are needed to shed light on the underlying mechanisms associated with sleep duration and MetS and examine if normalizing sleep duration reduces MetS risk in the general population.

Increasing evidence regarding the association between MetS and mortality confirmed the association between MetS and a higher risk of all-cause mortality and CVD mortality among older subjects (38). Besides, a growing body of suggests that elderly patients with MetS present a higher incidence of CVEs than those without the condition (39, 40), warranting the need to identify and manage individual risk factors for CVEs among elderly patients with MetS. Many strategies, including lifestyle changes, might effectively decrease CVEs among subjects with metabolic syndrome. Clinical trials demonstrated that intensive lifestyle modifications, such as increased physical activity and dietary changes, can reduce the risk of CVEs (41). However, in our study, the beneficial effect of physical activity on CVEs was only significant in elderly male patients with MetS, despite multiple previous studies identifying the protective effect of physical activity on CVEs (42–44). The Mediterranean-style diet, as a recommended dietary pattern, was associated with a reduced risk of CVEs (45), as patients with MetS following this diet significantly reduced body weight, WC, BP, plasma glucose, total cholesterol, and TG, as well as improved HDL-C concentration (46). The meta-analysis also confirmed that increased vegetable and fruit intake was positively correlated with a reduced risk of stroke and CHD (47). In addition, data in our analysis established soybean and soybean product consumption as beneficial predictors of CVEs in both genders. Barańska et al. found that soy and its isoflavones can effectively correct changes in the lipid metabolism in postmenopausal women and may favorably influence the prevention of CVEs (48). The second effective strategy included abstaining from drinking. In our study, alcohol consumption was a common predictor of CVEs in both genders, confirming the necessity to quit drinking alcohol in older stages of life. In the case of elderly male patients, being descendants of the Han race was a protective predictor of CVEs, coinciding with many previous studies. One review suggests that cardiovascular complications are more influenced by genetics and culture than diabetes mellitus and hypertension (49). Minority races in China prefer consuming meat because of weight problems and dyslipidemia, which presents a higher risk of developing CVEs. Moreover, a relatively higher annual income was associated with a lower risk of developing CVEs in elderly male patients with MetS. Shin et al. reported that low income and uncontrolled blood pressure are associated with increased all-cause and cardiovascular mortality and cardiovascular events in patients with hypertension (50). Similarly, diabetes combined with low income was associated with substantially elevated mortality risk, myocardial infarction, and ischemic stroke among primary care patients with hypertension (51). These findings collectively indicated that income is an essential aspect of social determinants of health that impacts cardiovascular outcomes in the care of MetS.

The strengths of this study include a prospective follow-up design, a defined length of follow-ups, and validated methods for determining cardiovascular events. Our study identified novel associated risk factors and predictors of newly diagnosed MetS and CVEs among elderly patients with MetS at baseline. Next, we aimed to determine effective strategies to decrease the incidence of MetS and CVEs among rural elderly patients. As shown in our study, in addition to the traditional risk factors such as dyslipidemia, hyperglycemia, hyperuricemia, hypertension, and obesity, we found soybean consumption to have a potential beneficial effect on preventing MetS and CVEs. Future studies should identify the amounts of soybean products sufficient to be given beneficially without causing MetS and CVEs.

There were some limitations in the present study. First, we did not evaluate the possible effect of diet on MetS and CVEs. Second, there were some participant losses due to their failure to show up during the follow-up, which might cause bias in the predictive effect of MetS on CHD, stroke, or CVD. Third, HDL-C, LDL-C, triglyceride, and fasting plasma glucose were measured only one time during the baseline and follow-up examination, which might be imprecise and have resulted in random errors. Third, the diet just included meat and vegetable consumption, and the diet score was calculated to represent the diet pattern. There were many other components, such as dairy products and fruits, that were not assessed in our study. Finally, the results of this study cannot be generalized to other populations.

MetS cases were prevalent among the rural Chinese elderly patients, with the cumulative incidence being even higher than that in many developed or urban areas in China. Except for traditional risk factors such as BMI, FPG, LDL-C, SBP, and current smoking habits, sleep duration of >9 h/day and age was a protective factors for newly diagnosed MetS. Moreover, a history of stroke, 2–3 times/week of soybean and soybean product consumption, and alcohol consumption were good predictors of MetS in both genders in the elderly population. Race, LDL-C, uric acid, hemoglobin, 5,000–20,000 annual income, and heavy physical activity were also predictors of CVEs in male elderly patients.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Ethics Committee of China Medical University (Shenyang, China AF-SDP-07-1, 0-01). The patients/participants provided their written informed consent to participate in this study.

SY contributed to the data collection, analysis, and interpretation. XG and HY contributed to data collection. GL and SY contributed to the data analysis. YS contributed to the study's conception and design. All authors read and approved the final version of the manuscript.

This study was supported by grants from the National Key Research and Development Program from the Ministry of Science and Technology of China (Project Grant # 2018 YFC 1312400 and Sub-project Grant # 2018 YFC 1312403) and the ‘China Medical University Youth Backbone Program’ project funds (Grant No. QGZ2018037).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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