Prevalence of Cardiovascular Disease Risk Factor Clustering Among the Adult Population of China
Results From the International Collaborative Study of Cardiovascular Disease in Asia (InterAsia)
Background— The prevalence of cardiovascular disease (CVD) risk factors has been increasing in China.
Methods and Results— We examined the prevalence of CVD risk factor clustering among Chinese adults aged 35 to 74 years with data from the International Collaborative Study of Cardiovascular Disease in Asia (InterAsia), a cross-sectional survey of a nationally representative sample (n=14 690) conducted during 2000 to 2001 and compared these data with those of US adults from the National Health and Nutrition Examination Survey of 1999 to 2000. Overall, 80.5%, 45.9%, and 17.2% of Chinese adults had ≥1, ≥2, and ≥3 modifiable CVD risk factors (dyslipidemia, hypertension, diabetes, cigarette smoking, and overweight), respectively. By comparison, 93.1%, 73.0%, and 35.9% of US adults had ≥1, ≥2, and ≥3 of these risk factors, respectively. In a multivariate model including age, sex, and area of residence, the odds ratio (95% confidence interval [CI]) of having ≥1, ≥2, and ≥3 CVD risk factors versus none of the studied risk factors was 2.61 (95% CI, 2.09 to 3.27), 3.55 (95% CI, 2.77 to 4.54), and 4.97 (95% CI, 3.67 to 6.74), respectively, for Chinese adults 65 to 74 years old versus 35 to 44 years old; 3.65 (95% CI, 3.21 to 4.15), 4.67 (95% CI, 4.06 to 5.38), and 5.60 (95% CI, 4.70 to 6.67), respectively, for men compared with women; 1.18 (95% CI, 1.07 to 1.30), 1.34 (95% CI, 1.21 to 1.50), and 1.84 (95% CI, 1.60 to 2.12), respectively, for urban compared with rural residents; and 1.98 (95% CI, 1.76 to 2.22), 2.75 (95% CI, 2.42 to 3.13), and 4.36 (95% CI, 3.68 to 5.18), respectively, for residents of northern compared with southern China.
Conclusions— Clustering of CVD risk factors is common in China. Prevention, detection, and treatment of CVD risk factor clustering should be an important component of a national strategy to reduce the increasing burden of CVD in China.
Received October 18, 2004; revision received April 9, 2005; accepted April 12, 2005.
Cardiovascular disease (CVD) accounts for half of noncommunicable disease deaths worldwide, 16.7 million in 2002.1 Although CVD risk is perceived to be low in economically developing countries, ischemic heart disease and stroke were 2 of the 3 leading causes of mortality in such countries in 1990.1–3 In China, CVD accounted for nearly 40% of all deaths in 1994.3,4 Furthermore, CVD incidence and mortality in China are projected to increase substantially during the next 20 years.3
Although the prevalence of some CVD risk factors has decreased in economically developed countries, the corresponding prevalence has increased in economically developing countries.1,3 For example, in China, the prevalence of hypertension increased from 11.3% in 1991 to 27.2% in 2000.5,6 Furthermore, mean cholesterol levels have increased during the past decade, with the most recent report indicating that 23.8% and 9.0% of the Chinese adult population have a total cholesterol level between 5.2 mmol/L and 6.2 mmol/L and ≥6.2 mmol/L, respectively.7 China is currently undergoing rapid demographic, social, and economic changes that may further increase the burden of CVD.
In providing a context for policy planners and health education programs in economically developing countries, it is important to quantify the proportion of the population at high risk for CVD. Such data provide an understanding of the size of the population in need of targeted interventions to lower the population burden of illness due to CVD. The goal of this study was to quantify the proportion of Chinese adults who had 1 or more of the following major modifiable CVD risk factors: dyslipidemia, hypertension, diabetes, current smoking, and overweight in 2000 to 2001 and to determine the percentage of Chinese adults with a clustering of 2 or more and 3 or more of these risk factors. This was accomplished with the use of data collected in the nationally representative International Collaborative Study of CVD in Asia (InterAsia). To provide a context for these results, the prevalence of 1 or more and the clustering of 2 or more and 3 or more CVD risk factors among Chinese adults were compared with similar estimates obtained for US adults from the National Health and Nutrition Examination Survey (NHANES) of 1999 to 2000.
InterAsia has been described in detail previously.8 In brief, a 4-stage stratified sampling method was used to select a nationally representative sample of the general population of China. In the first stage, China was stratified into north and south, as delineated by the Yangtze River. Five provinces were chosen from each region, including the provinces of Beijing in the northern region and Shanghai in the southern region. Counties within each province were divided into urban and rural areas on the basis of administrative data. Areas that were as populated or more populated than the county’s capital served as urban areas, and towns that were less densely populated than the capital served as rural areas. In the second stage of sampling, 1 urban and 1 rural area from each province were selected. In the third stage of sampling, 1 street district or township was randomly selected from each urban and rural area. In the final stage of sampling, individual participants were selected for inclusion. Only 1 participant was selected from each household, without replacement.
A total of 19 012 persons were randomly selected from the 20 primary sampling units (street districts in urban areas or townships in rural areas) and invited to participate. A total of 15 838 individuals completed the survey and examination, a response rate of 83.3% (82.1% in men and 84.5% in women; 82.2% in urban areas and 84.4% in rural areas). Of these participants, 15 540 persons (7526 men and 8014 women) were aged 35 to 74 years. The overall response rate was similar among men and women and in urban and rural areas.
Data collection was conducted in examination centers at local health stations or in community clinics in the participant’s residential area. For a few individuals, the interview and examination were conducted during a home visit. During the study visit, trained research staff members administered a standardized questionnaire. Of relevance to the current analysis, the questionnaire assessed age; sex; education; cigarette smoking; a self-reported history of stroke, myocardial infarction, and congestive heart failure; and the previous diagnosis and treatment of hypertension, high cholesterol, and diabetes. Participants who reported having smoked ≥100 cigarettes during their lifetime were classified as current smokers if they answered affirmatively to the question, “Do you smoke cigarettes now?”
Blood Pressure Measurement
For each participant, 3 blood pressure measurements were obtained by a standardized protocol adapted from procedures recommended by the American Heart Association.9 Blood pressure was measured by trained physicians or nurses with participants in the seated position after they had rested for at least 5 minutes. Participants were advised to avoid alcohol, cigarette smoking, coffee, tea, and excessive exercise for at least 30 minutes before their blood pressure measurement. A calibrated mercury sphygmomanometer was used, and 1 of 4 cuff sizes (pediatric, regular adult, large, or thigh) was chosen on the basis of the participant’s arm circumference.9 Hypertension was defined as an average systolic blood pressure (SBP) ≥140 mm Hg and/or an average diastolic blood pressure (DBP) ≥90 mm Hg and/or self-reported current treatment for hypertension with antihypertensive medication.10,11
Height and Weight Measurement
Body weight and height were measured by trained observers following a standard protocol. Weight was recorded by trained staff members with a certified double-balance-beam scale placed on a firm, level surface. Height was measured with a Frankfort plane positioned at a 90° angle against a wall-mounted metal tape. Body mass index (BMI) was calculated as body weight (in kilograms) divided by height (in meters) squared. Overweight was defined as having a BMI ≥25 kg/m2.
Participants were asked to fast overnight before their study visit, and blood samples, to measure serum lipids and plasma glucose, were drawn by venipuncture. Blood specimens were processed at the field center and shipped to a central clinical laboratory in Beijing by air, where specimens were stored at −70°C until laboratory assays were performed. Total and HDL cholesterol and serum triglycerides were analyzed enzymatically with commercially available reagents.12 Lipid measurements were standardized according to the criteria of the Centers for Disease Control and Prevention–National Heart, Lung, and Blood Institute Lipid Standardization Program.13 For participants with a triglyceride level <4.5 mmol/L, LDL cholesterol levels were calculated from the Friedewald equation (LDL cholesterol=total cholesterol−HDL cholesterol−triglycerides/5). Dyslipidemia was defined as self-reported current treatment with cholesterol-lowering medication or having 1 or more of the following: total cholesterol ≥5.2 mmol/L, triglycerides ≥1.7 mmol/L, HDL cholesterol <1.0 mmol/L, or LDL cholesterol ≥3.4 mmol/L. For the glucose measurement, whole blood was collected in evacuated tubes containing NaF. Plasma glucose was measured with a modified hexokinase enzymatic method. Diabetes was defined as having a fasting plasma glucose level ≥7.0 mmol/L and/or self-reported current treatment with antidiabetes medication (insulin or oral hypoglycemic agents).
The Institutional Review Board at Tulane University Health Sciences Center approved the InterAsia study. In addition, ethics committees and other relevant regulatory bodies in China approved the study. Written, informed consent was obtained from each participant before data collection. Participants with untreated conditions, identified during the study, were referred to their usual primary healthcare provider.
All analyses were restricted to survey participants without a history of myocardial infarction, stroke, or congestive heart failure (excluded n=479) and were standardized to the age distribution for Chinese adults in the year 2000. Participants missing height, weight, total cholesterol, HDL cholesterol, triglycerides, glucose, or blood pressure measurements (n=371) were also excluded from the analyses, leaving a final study population of 14 690 Chinese adults for the current set of analyses. The prevalence of each CVD risk factor (dyslipidemia, hypertension, diabetes, current smoking, and overweight) was determined for men and women, separately, by age group (35 to 44, 45 to 54, 55 to 64, and 65 to 74 years), urban or rural residence, and northern or southern residence.
The prevalence of 0, 1, 2, and ≥3 CVD risk factors was determined for the overall study population and for men and women separately. Next, the percentage of the population with ≥1, ≥2, and ≥3 CVD risk factors was determined by age group (35 to 44, 45 to 54, 55 to 64, and 65 to 74 years), sex, rural or urban residence, and southern or northern residence separately. The significance of the differences in the prevalence of ≥1, ≥2, and ≥3 CVD risk factors across subgroups was compared with the Wald χ2 test. The adjusted odds ratios and 95% confidence intervals (CIs) of having ≥1, ≥2, and ≥3 major CVD risk factors versus no CVD risk factor were determined from multivariable logistic-regression models that included age group, sex, urban versus rural residence, and northern versus southern residence.
Next, the prevalence of each risk factor studied was compared for adults 35 to 74 years of age in China versus the United States, after standardization to the age distribution of Chinese adults in the year 2000 according to the Wald χ2 test. Estimates for the United States were calculated with data from the NHANES 1999 to 2000.14 The prevalence of having ≥1, ≥2, and ≥3 of the CVD risk factors studied was also determined for 35- to 74-year-old adults in the US population. The prevalence rates observed for US adults were compared with their counterparts in China, overall and by age group (35 to 44, 45 to 54, 55 to 64, and 65 to 74 years) and sex after standardization based on the age distribution of the year 2000 Chinese population. All analyses were conducted with methods appropriate to the complex survey design of InterAsia and NHANES with Stata 7.0 (Stata Inc) and SUDAAN 8.0.1 (SUDAAN) software.
Prevalence of CVD Risk Factors in China
In the Chinese population aged 35 to 74 years, the age-standardized prevalence of dyslipidemia, hypertension, diabetes, current smoking, and overweight was 53.6%, 26.1%, 5.2%, 34.4%, and 28.2%, respectively (Table 1). The age-standardized prevalence of overweight was higher in women than in men (P<0.001). Conversely, hypertension and smoking prevalences were higher in men than in women (both P≤0.001). Hypertension and diabetes prevalences increased with age among both men and women (each P for trend, <0.001). Among men, dyslipidemia, current smoking, and overweight decreased with age (each P for trend, <0.001 except dyslipidemia, P=0.060). Among women, dyslipidemia and current smoking increased for the entire age range (P<0.001), and overweight decreased with age (P=0.07). Dyslipidemia, hypertension, diabetes, and overweight were more common among men and women living in northern compared with southern China and in urban compared with rural areas (all P<0.001, except for diabetes among northern compared with southern men [P=0.519] and hypertension among urban compared with rural women [P=0.746]). In contrast, current smoking was more common among southern and rural residents of China compared with their northern and urban counterparts (each P≤0.001, except northern compared with southern men, P=0.115).
Prevalence of ≥1, ≥2, and ≥3 CVD Risk Factors in China
Overall, 10.5% and 28.7% of Chinese men and women, respectively, did not have any of the risk factors investigated (dyslipidemia, hypertension, diabetes, current smoking, or overweight; Figure 1). In contrast, 34.2%, 33.2%, and 22.0% of men and 35.1%, 24.0%, and 12.2% of women had 1, 2, and ≥3 of these risk factors, respectively. Overall, 19.5%, 34.6%, 28.7%, and 17.2% of Chinese adults had 0, 1, 2, and ≥3 of these risk factors, respectively. In total, 80.5% of the population had 1 or more CVD risk factors. The prevalence of ≥1, ≥2, and ≥3 major modifiable CVD risk factors was higher at older ages (Figure 2; each P<0.001). Also, the age-standardized prevalence of ≥1, ≥2, and ≥3 risk factors was higher among men and among urban and northern residents compared with women and rural and southern residents, respectively (all P<0.001).
The adjusted odds ratio of having ≥1, ≥2, and ≥3 major modifiable CVD risk factors versus none increased progressively with increasing age (Table 2). The adjusted odds ratios (95% CI) of ≥1, ≥2, and ≥3 CVD risk factors for persons 65 to 74 years of age compared with their counterparts 35 to 44 years of age were 2.61 (95% CI, 2.09 to 3.27), 3.55 (95% CI, 2.77 to 4.54), and 4.97 (95% CI, 3.67 to 6.74), respectively. In addition, after multivariable adjustment, males and urban and northern residents were more likely to have ≥1, ≥2, and ≥3 CVD risk factors compared with females and rural and southern residents, respectively (all P<0.001).
CVD Risk Factor Prevalence: United States– China Comparison
The age-standardized prevalence of overweight was almost 3-fold greater among adults in the United States (78.0%) compared with their counterparts in China (28.2%, P<0.001). In addition, the age-standardized prevalence of dyslipidemia, hypertension, and diabetes was higher among residents in the United States (67.1, 33.6%, and 8.0%, respectively) compared with their counterparts in China (53.6%, 26.1%, and 5.2%, respectively; each P<0.001). In contrast, a higher percentage of adults in China (34.4%) compared with the United States (23.5%) were current smokers (P<0.001).
The age-standardized prevalence of ≥1, ≥2, and ≥3 CVD risk factors was higher for adults in the United States (93.1%, 73.0%, and 35.9%, respectively) compared with their counterparts in rural (79.9%, 44.0%, and 15.4%, respectively) or urban (83.1%, 53.6%, and 24.5%, respectively; each P<0.001 comparing rural and urban adults in China with their counterparts in the United States; Table 3) China. Similar to observations from China, having ≥1, ≥2, and ≥3 CVD risk factors was more common at older age and among men compared with women in the United States. The prevalence of ≥1, ≥2, and ≥3 CVD risk factors was higher among adults in the United States compared with China in every age group and among men and women (all P<0.001).
The present study indicates that >4 in 5 (80.5%) Chinese adults aged 35 to 74 years have at least 1 of the following CVD risk factors: dyslipidemia, hypertension, diabetes, current smoking, and overweight. In addition, clustering of 2 or more or 3 or more of these risk factors was noted in 45.9% and 17.2% of Chinese adults, respectively. The significantly higher prevalence of ≥1, ≥2, and ≥3 risk factors in men compared with women may be due to the fact that 60.6% of Chinese men versus 6.8% of women were current smokers. The higher prevalence of ≥1, ≥2, and ≥3 CVD risk factors among urban and northern residents compared with their rural and southern counterparts reflects the fact that all of the CVD risk factors investigated, except for current smoking, were higher in urban and northern areas. Another striking difference was in the geographic variation of overweight among men and women. The prevalence of overweight was more common in northern and urban residents compared with their rural and southern counterparts.
High levels of CVD risk factors are common in many economically developing countries.15 In a study of 7 economically developing countries, as many as 78%, 46%, 50%, and 20% of adults in 1 or more countries were current cigarette smokers, had a high cholesterol level, were overweight, and had hypertension, respectively.15 These risk factors have emerged as important characteristics in predicting CVD morbidity and mortality in economically developing countries, including China.16 In previous studies, CVD incidence and mortality rates in China have been noted to be higher in northern and urban regions compared with southern and rural regions, respectively.17,18 Our finding of a higher prevalence of CVD risk factor clustering among residents of northern and urban areas of China is consistent with these studies.
Several studies in the United States have investigated the impact of risk factor clustering on CVD incidence, mortality, and quality of life.19–23 In these studies, CVD incidence and all-cause mortality increased substantially in the presence of progressively more risk factors. For example, with data from the First NHANES Epidemiologic Follow-up Study, the age-, race-, sex-, and education-adjusted relative risks of coronary heart disease during 21 years of follow-up in adults with 1, 2, 3, or 4 or 5 risk factors (high blood pressure, high cholesterol, diabetes, overweight, and current smoking) compared with their counterparts with none of these risk factors, were 1.6, 2.2, 3.1, and 5.0, respectively.23 More important, among participants with 1 risk factor in that study, >50% of the coronary heart disease and stroke incidence and all-cause mortality were attributed to the presence of this risk factor. The attributable risk was >70% for persons with 3 risk factors. In longitudinal studies, the presence of CVD risk factors at baseline has been associated with a diminished quality of life. After 26 years of follow-up, quality of life was substantially and progressively lower among participants of the Chicago Heart Association Detection Project in Industry Study with a greater number of CVD risk factors at baseline.19
A recent study by Liu et al16 presented a comparison of coronary heart disease event rates and risk factor prevalence in the Chinese Multiprovincial Cohort Study (CMCS) and the Framingham Heart Study. Ten-year coronary heart disease event rates for men and women enrolled in the CMCS were 1.5% and 0.6%, respectively. In contrast, men and women enrolled in the Framingham cohort had 10-year coronary heart disease event rates of 8.0% and 2.8%, respectively. Also, 59% of men in the CMCS smoked compared with 40% of men enrolled in the Framingham Heart Study. The prevalence of hypertension and high cholesterol was lower in the CMCS population compared with the Framingham study population, but the prevalence of diabetes was similar in the 2 cohorts. Our comparison of nationally representative samples of adults also identified the prevalence of smoking as being more common and that of dyslipidemia, hypertension, diabetes, and overweight as being less common in Chinese and US adults. To estimate the 10-year coronary heart disease risk associated with risk factor clustering among Chinese adults, we applied the recalibrated Framingham risk function to the InterAsia study population. Not surprisingly, the 10-year coronary heart disease risk increased with progressively more risk factors present and was 0.2%, 1.7%, 3.2%, and 10.4% for Chinese adults with 0, 1, 2, and ≥3 risk factors, respectively.
Despite the higher rate of cigarette smoking in China, a higher prevalence of risk factor clustering was noted among US adults. Effective smoking cessation programs in China could blunt the rapidly rising burden of illness from CVD morbidity and mortality in the near future. In addition, a comprehensive tobacco control policy including steps outlined in the World Health Organization’s Framework Convention on Tobacco Control could be the most effective mechanism for reducing cigarette smoking and preventing tobacco-related CVD in China. Also, given the increasing prevalence of hypertension, overweight, and dyslipidemia noted in China during recent years, risk factor clustering may be increasing at a rapid rate. A multifaceted approach of population and targeted approaches aimed at prevention, detection, and treatment of dyslipidemia, hypertension, diabetes, and overweight could substantially reduce the prevalence of each of these risk factors, risk factor clustering, and morbidity and mortality from CVD in China. Furthermore, initiatives aimed at improving the composition of processed food (eg, salt and fat reduction) through industry regulation and legislation may prove to be an effective approach for improving the cardiovascular health of Chinese adults.
Participants with a history of myocardial infarction, stroke, or congestive heart failure were excluded from our analyses to permit a focus on the burden of CVD risk factors among patients without clinical CVD. Nonetheless, results were markedly consistent when participants with existing CVD complications were included in the analyses. Specifically, when these participants were included, the prevalence of ≥1, ≥2, and ≥3 risk factors was slightly higher (80.8%, 46.4%, and 17.6%, respectively), but the associations of age, sex, and geography with risk factor clustering were not substantially changed. In addition, despite a previous report by our group that a BMI ≥24 kg/m2 may best define overweight among Chinese adults, we chose to define overweight as a BMI ≥25 kg/m2 for the current analyses. A BMI cutpoint of 25 kg/m2 was selected to provide a prevalence of risk factor clustering that would be comparable to other populations (eg, US adults). When analyses defining overweight as a BMI ≥24 kg/m2 were repeated, 82.7%, 49.8%, and 20.0% of Chinese adults had ≥1, ≥2, and ≥3 risk factors, respectively. Finally, we chose not to include physical inactivity as a CVD risk factor in the current analyses because it is causally involved in the development of all CVD risk factors studied, except cigarette smoking. Inclusion of physical inactivity as a risk factor would have artificially inflated the prevalence of CVD risk factor clustering in China.
The strengths of InterAsia include the fact that its results are based on findings in a large, representative sample of the Chinese adult population, which allows for calculation of nationally representative estimates. In addition, a high response rate was achieved, standard protocols and instruments were used, the training and certification requirements for data collection were strict, and a vigorous quality assurance program ensured that high-quality data were collected. Given all of these requirements, the InterAsia data probably provide the most accurate current estimates for the general Chinese adult population. In addition, it was possible to assess the prevalence of several CVD risk factors. A limitation of the study was its reliance on estimates derived from a cross-sectional study. Cross-sectional studies do not allow for quantification of the importance of risk factor clustering in the incidence of CVD. However, previous studies have demonstrated the importance of these risk factors to the development of CVD in Chinese adults.16
CVD is a leading cause of mortality in China. Overall, 80.5%, 45.9%, and 17.2% of the adults in China have ≥1, ≥2, or ≥3 of the 5 CVD risk factors investigated in the current study, respectively. Effective population-based interventions such as smoking cessation, improved diet, and increased physical activity can safely and effectively lower the risk of CVD.24,25 Programs to enhance efforts aimed at prevention, detection, and treatment of dyslipidemia, hypertension, diabetes, smoking, and overweight may greatly reduce the future burden of CVD in the Chinese population.
The InterAsia study was funded by a contractual agreement between Tulane University, New Orleans, La, and Pfizer Inc, New York, NY.
Dr Reynolds is employed by and holds stock in Pfizer, Inc, which develops and markets treatments for cardiovascular disease. This study does not specifically examine any Pfizer products. Several researchers employed by Pfizer, Inc, were members of the Study Steering Committee that designed the study; however, the study was conducted, analyzed, and interpreted by the investigators independently of the sponsor.
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