The Prevalence of Metabolic Syndrome in Chinese Women over 50 Years Old Deserves More Attention

Aims This study aimed to understand the characteristics of metabolic syndrome (MetS) in populations (especially females) over 50 years old in Xi’an, China, to avail adjusting prevention strategies in similar regions. Methods 3001 people were included, based on data from “Xi'an Community-Based Management of Diabetes in the Elderly”. The prevalence rate was calculated and analyzed stratifying by gender, age and geography. Results The overall prevalence rates for males and females were 41.9±8.3% and 41.4±11.3% according to 2019 Chinese Diabetes Society diagnosis criteria, 32.0±9.0% and 49.7±9.8% according to International Diabetes Federation diagnosis criteria. The prevalence increased with age in females, but not in males. The prevalence of MetS, as well as abdominal obesity and hypertension, was higher in rural females than in urban and suburban females. Logistic regression analysis showed the risk factors included age, premature menopause, low family income and education level, sedentary time >9 hours/day, weight-gain, and family history of hypertension. Conclusions In Xi'an, China, under the current social-economic conditions, the prevalence of MetS in females over 50 of age stands higher level than that males, and the prevalence in rural females is higher than more attention.

Through the efforts invested in prophylaxis and treatment of CVD, its prevalence and mortality in males have declined. However, the prevalence of CVD in females is gradually increasing, as is the associated medical burden. 3,4 Therefore, we should focus on the prevalence and pathogenesis of CVD in females and develop gender-effective prevention and treatment strategies.
Metabolic syndrome (MetS) is an important risk factor for CVD, death, heart failure, and stroke. [5][6][7] Previous studies have shown a higher prevalence of MetS in males than in females. However, studies on the gender difference in prevalence in the elderly, which applied stratification analysis, yield inconsistent results. Moreover, a review of the national and international studies on the prevalence of MetS shows differences in the prevalence and disease characteristics in different regions, ethnic groups and populations with different living habits. 8 Our research team used the data of the Xi'an Community-Based Management of Diabetes in the Elderly (Xi'an CBMDE Project) to analyze the prevalence of MetS in people aged over 50 years in Xi'an, China, with a focus on females.
We aim to characterize the prevalence of MetS in populations with similar geographical characteristics and living habits in the Xi'an region in China and provide a better understanding of MetS to improve prevention strategies for MetS.

Study population
This study used the data of the Xi'an CBMDE Project to analyze the prevalence of MetS, a prospective cross-sectional study employing a community-based multi-stage, stratified, cluster sampling method that started in June 2014 and ended in September 2016. The project aimed to sample diabetes patients aged over 50 years, representatives of the community (or rural areas) in Xi'an and its surroundings over the long-term follow-up.
Because the prevalence of MetS is significantly higher than the prevalence of diabetes, the data from this project are sufficient to analyze the prevalence of MetS.
Sampling process: The first step was a non-random selection of areas: 4 urban districts, 3 suburbs and 2 rural areas (1 high-income rural area and 1 low-income rural area) were chosen. The second step entailed the non-random selection of specific communities and villages from the selected areas. A total of 7 communities and 7 rural villages were selected (4 urban and 3 suburban communities, 1 wealthy (large) and 6 poor (medium and small) villages). In the third step, in each selected community or village, the population was stratified according to the distribution characteristics of the population of the selected community (or village). Using simple and random sampling at each level, cluster sampling was performed using the building (or natural village) as the basic unit. A total of 3,119 urban and rural residents aged 50 years and over (response rate of 75.45%) were selected, and 3,001 participants were included after 118 people with missing fasting plasma glucose (FPG), 2-hour postprandial glucose (2hPG) and glycated hemoglobin data were excluded. This study was approved by the Xijing Hospital Ethics Committee (No. 20130925-8). All study subjects signed informed consent.

1.
Questionnaire included: demographic data, family medical history, current medical history, and health information.

2.
Physical examination: height was measured with the participants standing barefoot; weight, waist circumference, and hip circumference were measured with the subjects wearing underwear and standing with their feet separated; the blood pressure was measured twice in the right arm after a 5 min rest, and the average was taken.

3.
Specimen collection and analysis: after overnight fast, 5 ml of venous blood was collected into an anticoagulant tube, and the plasma was separated and stored at 4 o Blood glucose, blood lipids, blood uric acid, liver and kidney function were measured with an automatic biochemical analyzer (present in the laboratory of class A tertiary hospitals in each sub-center) on the same day.

5.
Quality control: the investigators were trained and examined before joining the study. Each examination center was quality-controlled by the country. The blood analysis was performed by qualified personnel.

General information
A total of 4,147 people aged over 50 years were recruited. The overall response rate was 75.47%. The analysis of MetS was limited to individuals with complete physical measurements and laboratory data, a total of 3,001, including 1,086 males and 1,915 females (Table 1).
Gender differences in the prevalence of the MetS in the elderly population in Xi'an, China (Figure 1) According to the 2019 CDS criteria, the MetS prevalence rate was 41.9±8.3% and 41.4±11.3% in males and females, respectively. Gender differences stratified by age in the prevalence of the MetS in the elderly population (2019CDS) is presented in Figure 2.
The prevalence in men was higher than in women in  Figure 3. The crude and age-stratified prevalence rates were all significantly higher in females than in males. The prevalence of MetS in females, but not in males, increased with age.
Regional differences in the prevalence of metabolic syndrome in women MetS prevalence was the highest in rural females aged over 50 years. The prevalence in elderly females in urban, rural and suburban areas increased with age when the 2019 CDS criteria were used. According to the IDF criteria, MetS prevalence in females followed the same trend in age groups 50-59 and 60-69 years. The prevalence in rural women over 70 years old was lower than in the 60-69 years age group, possibly due to increased mortality in this age group (Table 2).
Abdominal obesity and hypertension were the most prevalent in elderly rural females. The prevalence of hypertriglyceridemia was comparable between rural and urban females and higher than in suburban females. The prevalence of hyperglycemia was lower in rural women than in urban and suburban women (Table 3).

Demographic and lifestyle characteristics of females from different areas
Besides age, the results may be influenced by other factors.The education level and family income of elderly females from rural areas were significantly lower than those from urban and suburban areas. The rural population showed a later menarche age and an earlier menopause age than urban and suburban populations. More rural women had menopause before the age of 45 years than urban and suburban women (  (Table 4).
Interestingly, elderly rural women reported a lower incidence of family history of diabetes, hypertension, and dyslipidemia than urban and suburban women. The rural females had the highest mean waist circumference, systolic and diastolic blood pressure; triglyceride levels; and the lowest blood glucose levels (Table 4), consistent with the higher prevalence of abdominal obesity, hypertension and hypertriglyceridemia in rural females than those in the urban and suburban females (Table 3).
After a comparative analysis of the demographic data, dietary and lifestyle patterns of elderly females from different areas, logistic regression analysis was performed for possible risk factors for MetS ( in urban residents than in rural residents. [12][13][14]23,24 However, the results of the 2013-2014 nationwide MetS epidemiology study showed a higher prevalence of MetS in the rural population than in the urban population. 15 Similar trends have been observed worldwide.
It was previously believed that the incidence of obesity in economically developed countries was high; however, this view is outdated in the current world with a highly developed economy. Although ours was a regional study, the difference in prevalence among females in different areas is consistent with the results of epidemiological studies for the whole country and even some regions of the world, indicating that our findings are representative. With the development of a global social economy, food shortages and physical labor demands are decreasing, and the incidence of obesity and MetS has shifted to developing countries. 25 In developed countries, people's understanding of healthy lifestyles is deepening, health management is advancing and disease prevention and control measurements are being strengthened, resulting in the stabilization and gradual decline in the previously rapidly increasing MetS prevalence. 26 We may expect such trends in the developed regions of China, such as Beijing and Shanghai. Rural areas, suburbs or small cities develop economically and living standards improve. However, due to a lack of awareness of healthy lifestyle choices, people consume large amounts of energy-dense foods, such as oils, carbohydrates, and sugary drinks. 25,27 At the same time, physical activity has declined, resulting in an increased incidence of obesity and MetS. With the migration of rural populations to cities, changes in dietary patterns and a reduction in physical activity occurred, and the prevalence of insulin resistance, obesity, hypertension, type 2 diabetes, dyslipidemia, and coronary heart disease increased. 28 Lifestyle changes that occur during socio-economic development increase the prevalence of MetS.
Therefore, prevalence changes in economically developed and developing regions may be a historical phenomenon. Within a specific historical period, people in developing regions, such as rural areas, show a higher prevalence of MetS than people in economically developed regions, such as cities. After observing such a pattern, it is crucial to strengthen the advocacy for healthy lifestyles during the process of social and economic advancement to provide better health options towards better living and reduce health care costs for chronic diseases. The US Cholesterol Project has demonstrated that through policies, publicity, and health care at the national level, the control of blood lipid levels and hypertension could be improved nationwide. 29 The prevention and control measures undertaken for chronic diseases in the past 10 years in China were effective. 15,27 Therefore, we should shift the focus to the rural population, which is experiencing a lifestyle change, and implement appropriate national policy, guidance, publicity, and health care system. As a result, people in developing regions will be able to live a healthy and prosperous life.

Consent for publication
Not applicable Availability of data and materials The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no conflict of interests.      Figure 1 According to the 2019CDS diagnostic criteria, there was no significant difference in the prevalence rate between men and women over 50 years old, P=0.787.
According to the IDF diagnostic criteria, the prevalence rate in women over 50 was significantly higher than that in men, P < 0.001.

Figure 2
According to the 2019CDS diagnostic criteria, the prevalence rate in the 50-59 age group was significantly lower in females than in males (P < 0.001). In the 60-69 age group, there was no significant difference in the prevalence rate between females and males, P=0.062. In the group ≥70 years old, the prevalence rate in females was significantly higher than that in males, P=0.007.There was no significant difference in prevalence among men aged 50-59, 60-69 and ≥70 years, P=0.530.There was a significant difference in prevalence among female age groups, P < 0.001, and the prevalence increased with age.

Figure 3
According to the IDF diagnostic criteria, the prevalence rate of women was significantly higher than that of men in the 50-59 year group, the 60-69 year group and the ≥70 year group, P=0.024, P < 0.001 and P < 0.001.There was a significant difference in prevalence among men aged 50-59 years, 60-69 years and ≥70 years (P=0.035), but no increase with age was observed. There was a significant difference in prevalence among female age groups, P < 0.001, and the prevalence increased with age.