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Abstract
Objectives This study aimed to determine the changing prevalence of clustering of cardiovascular disease (CVD) risk factors across socioeconomic spectra in rural southwest China.
Design Data were collected from two waves of cross-sectional health interviews and examinations among individuals aged ≥35 years in rural China. Anthropometric measurements, blood pressure and fasting blood sugar levels were recorded for each participant.
Setting This study was conducted in rural Yunnan Province of China.
Participants 8187 individuals in 2011 and 7572 in 2021 consented to participate in this study.
Results From 2011 to 2021, prevalence increased of hypertension (26.1% vs 41.6%), diabetes mellitus (5.9% vs 9.8%), obesity (5.9% vs 12.0%) and central obesity (50.0% vs 58.3%) (p<0.01), while prevalence decreased of current smoking (35.2% vs 29.6%), secondhand smoke exposure (42.6% vs 27.4%) and current drinking (26.6% vs 29.6%) (p<0.01). This decade also saw an increase in the prevalence of participants with clustering of ≥2 (61.8% vs 63.0%) and ≥3 CVD risk factors (28.4% vs 32.2%) (p<0.05). These increasing rates were also observed among subgroups categorised by sex, ethnicity, education level, income level and those ≥45 years of age (p<0.05). In both 2011 and 2021, male participants and participants with a lower education level had higher prevalence of clustering of ≥2 and ≥3 CVD risk factors than their counterparts (p<0.01). Ethnic minority participants and participants with higher annual income had higher prevalence of clustering of CVD risk factors in 2011 but presented opposite associations in 2021 (p<0.01).
Conclusion The prevalence of clustering of CVD risk factors increased substantially across all socioeconomic spectra in rural southwest China from 2011 to 2021. Future efforts to implement comprehensive lifestyle interventions to promote the prevention and control of CVD should in particular focus on men, those of Han ethnicity and those with low socioeconomic status.
- Cardiac Epidemiology
- EPIDEMIOLOGY
- PUBLIC HEALTH
Data availability statement
Data are available upon reasonable request. Not applicable.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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STRENGTHS AND LIMITATIONS OF THIS STUDY
This present research is the first study to examine the role of individual socioeconomic status in temporal trends of prevalence of clustering of cardiovascular disease (CVD) risk factors in the southwest Chinese population.
There was a high response rate (over 97%) in this study.
Our large sample size enhances the validity of our results.
The present study focused on seven selected risk factors, so the full range of risk factors attributable to CVD was not captured.
Introduction
Cardiovascular disease (CVD) is the leading cause of death worldwide with an estimated 17.9 million deaths, accounting for 32% of global mortality in 2019.1 2 In China, in 2019, more than 120 million suffered from CVD, and 4.58 million died from CVD. Moreover, the burden of CVD in China is on the rise due to its rapidly ageing population and major lifestyle changes over the last two decades.3 This large and growing problem has placed a heavy burden on the Chinese health system.
Previous studies have established that multiple modifiable CVD risk factors make a significant contribution to increased burden of CVD. In accordance with studies from other countries,4–6 hypertension, diabetes mellitus, smoking, alcohol consumption, physical inactivity, and being overweight or obese are well recognised as major modifiable CVD risk factors in China. These modifiable CVD risk factors may occur either in single or multiple numbers, and the co-occurrence of multiple modifiable risk factors increases the risk of CVD morbidity or mortality. Clustering of two or more CVD risk factors is common in China, and the magnitude of CVD accountable to modifiable risk factors is rising as the prevalence of risk factors increases.7–9
There is a strong relationship between individual socioeconomic status (SES) and prevalence of CVD risk factors. Those with low SES have been found to have higher prevalence of CVD risk factors than those in higher SES groups in high-income countries, regardless of the particular indicators of SES used in the studies.10 11 In contrast, both positive and negative associations between individual SES and prevalence of CVD risk factors have been uncovered in some low/middle-income countries.12 13 However, there has been limited evidence on how clustering of CVD risk factors differs by individual SES. Specifically, little research has been conducted to examine how prevalence of clustering of CVD risk factors changes over time, and the relationship between SES and temporal trends of clustering of CVD risk factors remains unclear.
Thus, the aims of this study were to determine trends in prevalence and clustering of CVD risk factors in Yunnan Province, China from 2011 to 2021, and to examine how socioeconomic differences relate to the changing prevalence and clustering of CVD risk factors over time.
Methods
Data sources and study population
The primary data in this study were obtained through two waves of Yunnan Provincial Community Health Survey cycles conducted in three rural areas of Yunnan Province across two time periods, separated by a decade: 2010–2011 and 2020–2021. Located in southwest China, Yunnan Province is one of China’s least developed provinces. It is also home to 25 of China’s 56 state-recognised ethnicities, with a total province population recorded at 48 million people in 2020.
In 2011, all counties in Yunnan were classified into three categories according to their wealth distribution (per capita gross domestic product): low, medium or high. One county was then randomly selected from each of these categories for a total of three counties. To choose study participants ≥35 years from the three selected rural counties, a three-stage stratified random sampling selection process was then employed. Detailed description of this sampling method has been published previously.14 In 2021, the survey used a consistent three-stage stratified random sampling method to choose the study participants from the same three rural counties.
Data collection and measurement
The two surveys used a similar questionnaire, and laboratory investigations and anthropometric measurements were collected in both study years. All consenting participants were interviewed in person by trained interviewers using a structured, pretested questionnaire to gather information on demographic characteristics (age, sex, ethnicity, household income and education level), smoking and drinking habits, and family history of CVD.
Fasting blood glucose (FBG) was measured by local healthcare workers at community clinics. Detailed descriptions on the FBG measurement methodology have been reported in previous research.14
Blood pressure (BP) was measured using the American Heart Association protocol.15 Three consecutive measurements of systolic and diastolic BP were taken, and recorded BP levels were derived from the average of these three BP readings. This procedure has been detailed previously.16 This method differs slightly from the WHO MONICA standard and Health Survey for England/Scotland standard, both of which average the second and third measurements and reject the first measurement.17 Height, weight and waist circumference (WC) were measured following the WHO STEPS manual.18 Body mass index (BMI) was calculated as weight in kilograms divided by height in metres squared (kg/m2). The text reproduces information already reported in detail elsewhere.19 20
Patient and public involvement
Patients or members of the public were not involved in this study.
Definitions
Diabetes mellitus was defined as an FBG ≥7.0 mmol/L (126 mg/dL), reported use of antidiabetic medications within the previous 2 weeks, and/or reported previous diagnosis of diabetes mellitus by a health professional.21 Hypertension was defined as a mean systolic BP ≥140 mm Hg, diastolic BP ≥90 mm Hg, and/or the use of antihypertensive medications.22
BMI was classified based on the WHO recommendations for Asian adults23 using the following categories: normal (18.5–24.9 kg/m2), overweight (25–27.9 kg/m2) and obese (≥28 kg/m2). Central obesity was defined as a WC of more than 90 cm in men and more than 80 cm in women, in accordance with WHO recommendations for Asian adults.24
Participants who had smoked 100 or more cigarettes in their lifetime and smoked any form of tobacco product on a daily basis during the survey period were defined as current smokers. Exposure to secondhand smoke (SHS) was defined as non-smokers who reported being exposed to another person’s tobacco smoke at home or at work for a minimum of 15 min at least 1 day per week. Current drinker was defined as a person who drank alcohol regularly on 12 or more days during the 12 months preceding the survey.
Seven modifiable CVD risk factors were analysed in the present study: hypertension, diabetes mellitus, smoking, SHS exposure, drinking, obesity and central obesity. Modifiable CVD risk factor clustering was grouped into four categories: 0 (no risk factor), ≥1, ≥2 and ≥3 CVD risk factors, as determined by the presence of the seven factors under investigation.
Ethnic minority was defined as having a different language, culture or religion from that of the majority Han population. Illiteracy was defined as the inability to either read or write a short simple statement about daily life, while level of education was classified into two categories: illiterate and primary (grades 1–6) or higher. Annual household income was divided into two categories: low and high, with the median value as the cut-off point. Age was also classified into three categories: 35–44 years, 45–59 years and ≥60 years.
Statistical analysis
Data were analysed with descriptive analysis techniques, Χ2 tests and t-tests. Mean values of FBG, BP, BMI and WC were expressed as mean±SD (
), while categorical variables were presented as counts and percentages. Age-standardised prevalence rates of risk factors were calculated by direct standardisation to the 2020 Chinese population aged ≥35 years. Differences in prevalence values for categorical variables were compared using Χ2 tests for independence, and were presented as a percentage with a 95% CI. T-tests were employed to analyse differences in continuous variables, with statistical significance set at two tailed (p<0.05). All data analyses were conducted using SPSS V.22.0 software.
Results
The total number of individuals aged ≥35 years invited to participate in the two survey waves was 8400 in 2011 and 7800 in 2021. Of these, 8187 in 2011 and 7572 in 2021 consented to participate, for an overall response rate of 97.5% and 97.1%, respectively.
Table 1 presents the general characteristics and mean values of BP, FBG and anthropometric measurements of the participants by survey year. The proportion of men, ethnic minorities and those with low annual household income among the study population did not differ between the two survey years (p>0.05), whereas the adult illiteracy rate in women decreased from 42.2% in 2011 to 27.7% in 2021 (p<0.01). However, women consistently had a higher adult illiteracy rate than men in both survey years (p<0.01). From 2011 to 2021, statistically significant increasing trends in mean weight, BMI, WC, systolic BP, diastolic BP and FBG levels were observed both in men and women.
General characteristics and mean value of BP, FBG and anthropometric measurements in the Yunnan Provincial Community Health Survey study population by survey year
Table 2 presents the distribution of age-adjusted prevalence of the seven studied CVD risk factors by sex and survey year. In both 2011 and 2021, prevalence of current smoking and current drinking was much higher in men than in women (p<0.01), whereas women had higher prevalence of SHS exposure, obesity and central obesity than men (p<0.01). Further, current smoking was the top leading CVD risk factor in men, while central obesity was the top leading CVD risk factor in women. From 2011 to 2021, the prevalence of hypertension, diabetes mellitus, obesity and central obesity increased significantly both in men and women (p<0.01), while both men and women experienced significant declines in prevalence of current smoking, SHS exposure and current drinking (p<0.01). The gender difference in prevalence of hypertension was not significant in 2011, but men had higher prevalence of hypertension than women in 2021 (p<0.01).
Distribution of age-adjusted prevalence of seven CVD risk factors by sex and survey year in rural southwest China
Table 3 outlines age-adjusted prevalence of clustering of CVD risk factors by survey year and socioeconomic status. Overall, the prevalence of total participants with clustering of ≥2 and ≥3 risk factors increased from 61.8% and 28.4% in 2011 to 63.0% and 32.2% in 2021 (p<0.05). These increasing rates were also observed among the subgroups categorised by sex, ethnicity, education level, income level and age (participants aged ≥45 years) (p<0.05), with the largest relative increases occurring among Han ethnicity participants, illiterate participants and participants with lower annual household income levels (p<0.01). In contrast, participants aged ≥35–44 years experienced declines in prevalence of clustering of ≥2 and ≥3 risk factors (p<0.05). In both 2011 and 2021, male participants and participants with lower education levels continued to have higher prevalence of clustering of ≥2 and ≥3 risk factors than their counterparts, and clustering of CVD risk factors increased with age (p<0.05). Moreover, ethnic minority participants and participants with higher annual income had a higher prevalence of clustering of CVD risk factors in 2011, but presented opposite associations in 2021 (p<0.01).
Age-adjusted prevalence of clustering of CVD risk factors by survey year and socioeconomic status in rural Yunnan Province, China
Discussion
The findings indicate prevalence of modifiable CVD risk factors shifted over time, with the rural southwest Chinese adult population experiencing significant increases in prevalence of hypertension, diabetes mellitus, obesity and central obesity, but reductions in prevalence of current smoking, SHS exposure and current drinking from 2011 to 2021. Further, prevalence of clustering of CVD risk factors rose markedly over the 10-year study period, with significant socioeconomic differences in temporal trends for the observed rate.
In male participants, current smoking was the top CVD risk factor in 2011, followed by current drinking. The prevalence of current smoking and drinking in men (70.1% and 49.0% in 2011 and 58.6% and 31.1% in 2021) across the study period was higher than the prevalence rates observed in urban Chinese populations24 as well as that observed in other Asian countries,25 26 and men had a markedly higher prevalence of smoking and drinking than women. Such sex differences in smoking and drinking are well recognised worldwide: studies in Asia (including China) and western countries have established many more men than women smoke and drink.23 27 While smoking among women in the study region was at a much lower rate than men, the rate of exposure to SHS among women was higher than among men across the 10 years studied, indicating exposure to SHS is a serious and growing challenge for women. Encouragingly, prevalence of current smoking, current drinking and exposure to SHS significantly declined both in men and women over the 10-year study period, indicating comprehensive tobacco control strategies and health education on awareness of tobacco and drinking hazards have achieved progress in rural China. However, as smoking remains prevalent in the study population, robust smoking cessation programmes should be continued in rural southwest China.
Our study revealed that the overall prevalence of hypertension and diabetes mellitus in the study population (41.6% and 9.8%) was higher than the prevalence rates observed in other parts of rural China28 as well as in other low-income populations.5 6 29 30 Further, prevalence of hypertension and diabetes mellitus significantly increased in both men and women from 2011 to 2021. This increasing trend in prevalence of hypertension and diabetes mellitus was greater among men than women, indicating the emerging hypertension and diabetes mellitus epidemic in the study region is particularly acute for men. This possibly results from the fact that central obesity was more prevalent than obesity in the study population, and prevalence of obesity and central obesity also rapidly increased in both men and women from 2011 to 2021, with men experiencing higher increases in prevalence of central obesity than women. The importance of obesity as a major CVD risk factor has received considerable attention, and central obesity is more strongly associated with cardiometabolic risk factors and chronic disease risk than obesity.1 4 31 In this way, our findings highlight an urgent need for effective measures to prevent and manage obesity in rural southwest China, and present a great challenge for local governments to take on efforts to further control hypertension and diabetes mellitus in rural southwest communities.
Our results indicate that the prevalence of clustering of CVD risk factors was high, with 74.6% of male participants and 55.3% of female participants experiencing clustering of two or more investigated CVD risk factors. This rate is higher than that found in previous Chinese studies8 9 as well as studies from other Asian countries.5 6 Furthermore, clustering of CVD risk factors showed a clear increasing trend in both men and women from 2011 to 2021, indicating a potential future CVD epidemic in rural southwest China. The findings in this way suggest that future CVD prevention and intervention strategies should take comprehensive lifestyle interventions into account.
The present study found that men were more likely than women to present clustering of CVD risk factors. This gender difference in CVD risk factor clustering was also observed in several previous studies.5–9 Moreover, despite clustering of CVD risk factors showing a markedly increasing trend in both men and women from 2011 to 2021, men continued to have higher prevalence of clustering of ≥2 and ≥3 risk factors than women during the 10-year study period. This may have been due to the inclusion of tobacco and alcohol use as CVD risk factors in our study: as male participants smoked and drank more than women, this inclusion may have increased the risk factor clustering in men. The findings thus indicate that clustering of CVD risk factors is especially prevalent among men in rural southwest China, and gender is an important determinant that should be considered in future CVD prevention and control interventions.
The present study also revealed that clustering of CVD risk factors has increased substantially across people of all educational levels from 2011 to 2021 in rural Yunnan Province, with the largest relative increase rate occurring among participants with the lowest level of education. Participants with a lower level of education were more likely to present clustering of ≥2 and ≥3 risk factors than their more educated counterparts in both 2011 and 2021. This association of higher educational attainment with lower odds of clustering of CVD risk factors is in line with previous studies.8 9 29 This may largely be explained by the fact that education may influence health by improving one’s ability to use health information, and increased knowledge enables an individual to make healthier choices regarding their diet and physical activity. The results thus suggest CVD prevention strategies should focus in particular on individuals with low levels of education.
The present study also showed that both ethnicity and level of annual household income had apparent impacts on clustering of CVD risk factors. Despite the fact that prevalence of clustering of CVD risk factors increased among the subgroups categorised by ethnicity and income level during the 10-year study period, Han ethnicity participants as well as participants with lower annual household income had higher increases in prevalence than their counterparts. This rapid increase in CVD risk factor clustering in Han ethnicity and lower annual household income populations over the study period contrasts with the associations of ethnicity and income with clustering of CVD risk factors: ethnic minority participants and participants with higher annual income had higher prevalence of clustering of CVD risk factors in 2011, but presented inverse associations in 2021. The observed association of ethnicity with clustering of CVD risk factors may be explained by a combination of genetic, cultural, socioeconomic and lifestyle factors.7 16 The findings thereby underscore an urgent need for lifestyle interventions to head off an emerging epidemic of CVD in Han ethnicity and low-income populations.
Overall, this study indicated a strong relationship between individual SES and prevalence of clustering of CVD risk factors. Prevalence of clustering of CVD risk factors rose markedly across the entire SES spectrum over the 10-year study period, with the largest relative increase occurring among participants with low SES. This could result from the fact that a low SES was correlated with unhealthy lifestyle behaviours, poor health and low healthcare-seeking behaviour.10 12 13 The findings indicate a potential future CVD epidemic, especially among those with low SES in rural southwest China, and thus suggest future CVD prevention and intervention strategies focused on those with low SES.
The study findings are limited in several ways. First, the data collected and analysed were cross-sectional. Thus, we cannot draw conclusions about the causes of changes in CVD risk factor clustering observed. Second, the present study focused on seven risk factors. As it did not consider diet, hypercholesterolaemia, physical activity level or psychological factors among other potential risk factors to include, the full range of risk factors attributable to CVD was not captured. Further research is needed to examine the contribution of other risk factors to CVD in rural southwest China.
In conclusion, this study reveals that prevalence of clustering of CVD risk factors rose substantially in the decade from 2011 and 2021, with significant socioeconomic differences in temporal trends for the observed rate. The findings thereby suggest that future efforts to implement comprehensive lifestyle interventions to promote the prevention and management of CVD are urgently needed in rural southwest China, and should in particular focus on men, Han ethnicity populations and low SES populations.
Data availability statement
Data are available upon reasonable request. Not applicable.
Ethics statements
Patient consent for publication
Ethics approval
This study involves human participants and the Ethics Committee of Kunming Medical University approved this study prior to the commencement of research. Written informed consent was obtained from all participants for each of the two cross-sectional studies.
References
Footnotes
Contributors CL conceptualised the research idea and drafted the manuscript. LL contributed to the study design and provided comments on the paper during the writing process. G-hL, YZ and XW collected the data. ARG worked on the manuscript. All authors read and approved the final manuscript. Le Cai is responsible for the overall content as the guatantor.
Funding The data collection and analysis of this study were supported by grants from the National Natural Science Fund of China (grant number: 72064026), Program for Innovative Research Team of Yunnan Province (202005AE160002), and Union Specific Project Foundation of Yunnan Provincial Science and Technology Department, Kunming Medical University (202101AY070001-098).
Disclaimer The funders had no role in the study design, decision to publish or preparation of the manuscript.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.