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Objective: The aim of this study was to evaluate trends in BMI and the prevalence of overweight (BMI ≥ 25 kg/m2) and obesity (BMI ≥ 30 kg/m2) between 1991 and 1999–2000 among Chinese adults.
Methods and Procedures: In this study, two population-based samples of Chinese adults aged between 45 and 79 years (n = 7,858 during each period), and comparable in the distributions of age, gender, degree of urbanization, and region (North/South) were used. Height and weight were measured using identical procedures at each period, and BMI was calculated as weight (in kilogram) divided by height (in square meter).
Results: From 1991 to 1999–2000, the mean BMI increased from 21.8 to 23.4 kg/m2 among men and from 21.8 to 23.5 kg/m2 among women (each P < 0.001). Among men, the prevalence of overweight and obesity increased from 9.6 and 0.6%, respectively, in 1991 to 20.0 and 3.0%, respectively, in 1999–2000 (each P < 0.001). Among women, the prevalence of overweight and obesity increased from 14.5 and 1.8%, respectively, in 1991 to 26.5 and 5.2%, respectively, in 1999–2000 (each P < 0.001). The prevalence of overweight and obesity increased in all age groups, in rural and urban areas, and in North and South China, with greater relative increases in obesity among older age groups, South China, and rural areas (P interaction < 0.05).
Discussion: Overweight and obesity increased tremendously during the 1990s in China. These data underscore the need for national programs in weight maintenance and reduction, to prevent obesity-related outcomes in China.
China is undergoing rapid economic development. This has been accompanied by the adoption of “western style” dietary and physical activity behaviors (1,2,3). Along with these changes, a shift in disease burden from infectious to chronic diseases has occurred (4). At present, coronary heart disease, stroke, and cancer are the three leading causes of death in China, accounting for two-thirds of all deaths (4).
Obesity has been reported to be a risk factor for coronary heart disease, stroke, and cancer in Chinese adults (5,6,7). Nationally representative data from the InterASIA study for the year 2000 indicated that the prevalence of overweight and obesity in China was lower than in the United States (8,9). However, given the recent Westernization of Chinese habits, an obesity epidemic in China may be forthcoming. Knowledge of the trends in the prevalence of overweight and obesity is important in projecting the burden of these disorders in the future. Such data, in turn, can be used to plan rationally for the use of limited healthcare resources.
There have been few reports on recent trends in the prevalence of overweight and obesity in China, and these have assessed only urban centers in Northern China (10,11). The aim of this study was to examine the trends in overweight and obesity among a broad population-based sample of Chinese adults between 1991 and 1999–2000. These trends were assessed among the full samples, and stratified by gender, age group, region (North China vs. South China), and degree of urbanization (urban vs. rural). These data provide a preview of what may befall other economically developing populations, such as rural India and Sub-Saharan Africa.
Methods and Procedures
In 1991, the China National Hypertension Survey used a multistage random cluster sampling design to select a representative sample of the general Chinese population aged 15 years and older from all 27 provinces and 3 municipalities in China (12). A subset of this sample aged ≥40 years was included in the China National Hypertension Survey Follow-up Study (CHEFS). Of relevance to this analysis, CHEFS included a clinic visit involving the reassessment of lifestyle factors and anthropometrics in 1999–2000 among a subset of the original CHEFS sample. The data used in this study are derived from both baseline and follow-up examinations. The flow of study participants from the 1991 nationally representative sample to the population-based sample included in these analyses is presented in Figure 1. Overall, 8,442 participants, 45–79 years of age, had a follow-up examination in 1999–2000 with body weight and height measurements available for analysis. Because age, gender, and geography are related to BMI in China, participants who attended the 1999–2000 visit were frequency matched to their counterparts who attended the visit in 1991 based on strata of 5-year age groupings, gender, degree of urbanization (urban or rural), and region (North or South China). For strata which possessed more individuals at the 1991 examination than at the 1999–2000 examination, participants were chosen at random from 1991 for inclusion in these analyses, for a total of 7,858 participants included from each period. Region was determined as either north or south of the Yangtze River, and urban areas were defined as all cities, as designated by the central Chinese government, generally with a nonagricultural population of ≥100,000. The provinces included in this population-based sample were distributed across geographic regions in China representing various stages of economic development.
1991 and 1999–2000 examinations
Data were collected in 1991 and 1999–2000, during a single clinic visit at each time point by trained physicians and nurses using standardized methods with stringent levels of quality control (12). Data collection methods were identical at the two examinations, including use of the same standardized questionnaire for assessment of demographic characteristics. In addition, a standard protocol developed for the study was used for anthropometrics including body weight and body height at both time points. In brief, height and weight were measured with the participants in light clothing and without shoes. For measuring height, participants stood on a firm, level surface at a right angle to the vertical board of the height measurement device, and a height board mounted at 90 degrees to a calibrated vertical height bar was used (6). BMI was calculated as weight (in kilograms) divided by height (in square meters). For the primary analyses, individuals with a BMI ≥25.0 kg/m2 were considered overweight and individuals with a BMI ≥30.0 kg/m2 were considered obese. For secondary analyses, Asian-specific cut-points were used to define overweight and obese categories. Specifically, individuals with a BMI ≥24.0 kg/m2 were considered overweight and individuals with a BMI ≥28.0 kg/m2 were considered obese (13–15).
We certify that all applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during this research. This study was approved by the Tulane University Health Sciences Center's institutional review board and by corresponding regulatory bodies in China. Written informed consent was provided by all study participants at the 1999–2000 examination.
Demographic characteristics were compared between periods (1991 and 1999–2000) using the Wilcoxon rank-sum test for age, owing to its non-normal distribution, and the χ2-test for dichotomous variables (e.g., gender, degree of urbanization, and region). T-tests were used to compare mean body weight and BMI between periods, initially for men and women separately, and subsequently, after further stratification on the basis of age group. Next, the prevalence of overweight and obesity was calculated for each period, overall, and on the basis of gender, age group, degree of urbanization, and region. Comparisons of the change in prevalence across periods were made using the χ2-test. Next, prevalence estimates of overweight and obesity were calculated and stratified on the basis of gender, age group, degree of urbanization, or region, with estimates standardized for the other demographic and geographic characteristics. Direct standardization was performed using the 2000 China population aged 45–79 years as the standard population. The 2000 Chinese National Census data were used to derive the appropriate weighting on the basis of gender, age group, urbanization, and North/South distributions in the Chinese census, and the SUDAAN statistical software package (RTI, Research Triangle Park, NC) was used to calculate standardized prevalences and interactions. Differences in the proportional increase of the standardized prevalence of overweight and obesity from 1991 to 1999–2000 across age grouping, degree of urbanization, and region were tested via maximum likelihood estimation using multiplicative interaction terms.
Matching on age, gender, degree of urbanization, and region was successful (P > 0.6 comparing all factors in 1991 and 1999–2000). The mean age of participants was 57.8 years (range: 45.0–79.9 years) in 1991, and 57.7 years (range: 48.3–79.9 years) in 1999–2000. Also, at each period, 53% of the samples were men, 28% resided in urban areas, and 79% resided in North China.
Significant increases in mean body weight and BMI were observed from 1991 to 1999–2000 in all age groups and among both men and women (Table 1). In men and women, the mean increase in body weight was 2.5 and 2.2 kg, respectively, and the mean BMI increase was 1.6 and 1.7 kg/m2, respectively. The increases in body weight and BMI were incrementally larger at progressively older age groupings (all P ≤ 0.005 except body weight for men; P = 0.139).
Table 1. Mean (s.e.) body weight and BMI at 1991 and 1999–2000 by gender and age group
The prevalence of overweight and obesity increased between 1991 and 1999–2000 (Figure 2). Specifically, in 1991, 16.2% of men were overweight or obese compared with 28.1% in 1999–2000. The corresponding percentages for women were 17.2% in 1991 and 29.3% in 1999–2000. The proportional increase in overweight and obesity was even greater among men after data were standardized for age group, degree of urbanization, and region (Table 2). The prevalence of overweight and obesity significantly increased between 1991 and 1999–2000 in all age groups and among both men and women. In 1999–2000, 20% of men and 26.5% of women were overweight or obese (Figure 2, Table 2). Among men and women, the proportional increases in obesity were larger among older individuals compared to younger individuals.
Table 2. Standardizeda prevalence of overweight and obesity at 1991 and 1999–2000 by gender and age group
Increases in the prevalence of overweight and obesity were seen in urban and rural areas, and in North and South China (Table 3). In addition, relative increases in obesity were significantly greater among rural regions than urban regions and in South China than North China for both men and women.
Table 3. Standardizeda prevalence of overweight and obesity at 1991 and 1999–2000 by gender, degree of urbanization, and region
The prevalence of overweight and obesity was higher when the Asian-specific BMI cut-points were used. Similar to the primary analyses, the prevalence of overweight and obesity, using Asian-specific cut-points (BMI ≥ 24.0 kg/m2 for overweight and BMI ≥ 28.0 kg/m2 for obesity), increased markedly between 1991 and 1999–2000 (Figure 3).
These population-based data demonstrate marked increases in the prevalence of overweight and obesity in Chinese adults between 1991 and 1999–2000. These increases were present among all age groups, men and women, urban and rural settings, and within both Northern and Southern regions of China. In most subgroups, the prevalence of overweight and obesity had more than doubled over the study period.
Previous studies of trends in overweight or obesity within China have presented conflicting results. Concordant with this study, two analyses from the World Health Organization's Multinational Monitoring of Trends and Determinants in Cardiovascular Disease project demonstrated increases in mean BMI in Beijing across serial cross-sectional samples from 1984 to 1989 (10,16). In unadjusted analyses, Critchley et al. (2004) reported an increase in mean BMI from 23.9 to 24.9 kg/m2 (10). A separate analysis of the MONICA data standardized these values on the basis of age and sex to the world population, and suggested that a lesser increase, from 24.0 to 24.3 kg/m2, had occurred (16). This study demonstrated an increase in mean BMI from 21.8 to 23.3 kg/m2 among men and from 21.8 to 23.5 kg/m2 among women. The lower BMI values in 1991 present in this study, compared with that of the MONICA study, are likely a result of this study's inclusion of a broader sample of Chinese adults, including those from rural and Southern areas.
Analyses of the MONICA data also presented 8-year trends in the prevalence of overweight and obesity in Beijing from 1984 to 1993 and reported an age- and sex-standardized increase of 4.3 percentage points in overweight, but a decrease of 0.7 percentage points in obesity (16). A decrease in obesity was also found in serial cross-sectional analyses of the Tianjin population, whereby the prevalence of both overweight and obesity decreased over the period from 1989 to 1996 (11). Although both the MONICA and Tianjin studies used random sampling techniques, they are limited to urban areas in Northern China. This study included urban and rural areas within Northern and Southern China, finding significant increases in BMI, overweight, and obesity in all strata.
The increases in BMI and the prevalence of overweight and obesity may be because of the economic development in China, which has brought with it a high degree of Westernization of Chinese diet and lifestyle. Trend analyses of national dietary data in China from 1989 to 1997 indicate a substantial decrease in consumption of coarse grain and vegetables, and large increases in consumption of animal fat (17). Furthermore, the percentage of energy obtained from fat increased from 19.3 to 27.3% nationally, with urban residents obtaining 32.8% of their energy from fat in 1997. In addition, more recent data have shown that the proportion of the Chinese population living in urban areas increased from 26% in 1990 to 36% in 2000 and the number of cities in China has increased over that same period (18,19). This increasing urbanization is expected to continue (18), and will likely spur continued Westernization of dietary trends. This study demonstrated higher prevalence of overweight and obesity in urban areas than rural areas, as well as in Northern regions compared with Southern regions of China at both periods. However, the relative increase in obesity was higher among rural areas than urban areas and among Southern compared to Northern China. Therefore, Southern and rural China, areas which previously had lower cardiovascular disease (CVD) risk factor levels, may attain or even surpass obesity prevalence in Northern and urban areas in the near future should this trend continue.
Although older individuals still maintained lower prevalence of overweight and obesity than younger individuals, the current data showed higher increases in the prevalence of overweight and obesity among older individuals. Older individuals may be more apt to retain their nutritional and lifestyle characteristics longer than younger individuals during times of cultural transition. Therefore, had the current study been initiated in the previous decade, greater increases among younger individuals may have been present, as the first members of Chinese society to incorporate Western dietary and lifestyle characteristics.
The trends presented in this study represent significant public health implications for China. Data for Chinese adults from a large multicenter cardiovascular epidemiology study in China have shown that for each 2 kg/m2 increase in BMI, the risk of coronary heart disease increased by 23%, and the risk of ischemic stroke increased by 13%, while data from the CHEFS have shown that obesity (BMI ≥ 30 kg/m2) is associated with an ∼45% increased risk of CVD in men and a 30% increased risk in women (5,6). Obesity has also been linked to increased risk or prevalence of cancer, hypertension, dyslipidemia, and diabetes in Chinese adults (6,7,20,21). Some data suggest that an increased prevalence of CVD risk factors and diabetes and CVD risk occurs at lower BMI thresholds among Chinese adults compared with Western populations (13,14). However, data assessing the relationship between BMI and CVD and all-cause mortality from the CHEFS population have not confirmed the need for a lower BMI threshold among Chinese adults (6). Should future research demonstrate the need for a lower BMI threshold in the definitions of overweight and obesity among Chinese adults, the magnitude of the chronic disease burden which could be expected to result from the dramatic increases in the prevalence of overweight and obesity seen in this study would be even greater. When suggested Asian-specific cut-points for overweight and obesity were used in this study, the prevalence of overweight or obesity (from 1991 to 1999–2000) increased from 14.1 to 30.2% among men, and from 21.2 to 36.0% among women. Moreover, recent data comparing Chinese populations living in urban areas with those living in rural areas suggest that urbanization and westernization may increase susceptibility to the adverse effects of CVD risk factors (22). Of additional concern is the fact that data concerning children and adolescents have documented similar increasing trends in the prevalence of overweight and obesity. Specifically, in a study of children from seven Chinese provinces, the prevalence of overweight increased from 6.4 to 7.7% among 6- to 9-year olds and from 4.5 to 6.2% among 10- to 18-year olds between 1991 and 1997 (23). Previous data from the Bogalusa Heart Study have shown that overweight and obese children have a high likelihood of remaining overweight or obese into adulthood (24). Given that weight reduction in both Chinese children and adults has been shown to reduce the burden of chronic disease risk factors (25,26,27), urgent implementation of both weight control and obesity prevention programs in China is warranted.
This study should be viewed within the context of its limitations. Although recruitment for this follow-up study, nested within the 1991 Chinese National Hypertension Survey, was population-based, it did not employ sampling techniques necessary to consider the data nationally representative. Therefore, the prevalence estimates and changes provided in this report cannot be considered national estimates. However, the study included substantial numbers of urban and rural and Northern and Southern Chinese participants and is likely generalizable to Chinese adults 45 years and older. To our knowledge, this is the first and largest study to include men and women from both urban and rural areas from throughout Northern and Southern China. Previous studies of obesity trends have been limited to either urban areas or Northern China. Data on physical activity at follow-up and diet at either time points were not collected. Therefore, the degree to which decreases in physical activity and alterations in dietary intake may explain the increased prevalence of overweight and obesity could not be determined.
This study has several strengths. First, the current study of trends in overweight and obesity maintained a very large sample size and included individuals from urban and rural China, and Northern and Southern China. This, in conjunction with the population-based sampling of participants, makes the results of this study generalizable to the population of mainland China 45 years and older. In addition, the large sample size of this study allowed for assessing trends within specific population not previously reported, including gender, age group, degree of urbanization, and region. Second, the trends captured in this study occurred over a period of intensive Westernization and urbanization of Chinese culture. Both the generalizability and the time period under study make these data of tremendous clinical and public health relevance.
This study indicates a dramatic increase in the prevalence of overweight and obesity occurred among Chinese adults in the 1990s. This increase was observed among men and women, all age groups studied, in urban and rural regions, and in North and South China. The magnitude of the increases in the prevalence of overweight and obesity and the extensive reach to every population strata studied foretell a substantial increase in chronic diseases over the next several decades. These data call for immediate implementation of weight control and overweight and obesity prevention programs among Chinese adults to minimize the personal and economic burdens of chronic disease in China.
This study was supported by a national Grant-in-Aid (9750612N) from the American Heart Association (Dallas, TX), and partially supported by a grant (U01 HL072507) from the National Heart, Lung, and Blood Institute of the National Institutes of Health (Bethesda, MD), and by a grant (1999-272) from the Chinese Ministry of Health (Beijing, China) and by the Chinese Academy of Medical Sciences (Beijing, China). The sponsors did not play any role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.