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The objective of this study is to examine the trends in body mass index (BMI), waist circumference (WC) and prevalence of overweight (BMI 25 kg/m2 to 27.49 kg/m2), general obesity (BMI ≥ 27.5 kg/m2) and abdominal obesity (WC≥90 cm for men and ≥ 80 cm for women) among Chinese adults from 1993 to 2009. Data were obtained from the China Health and Nutrition Survey, which was conducted from 1993 to 2009 and included a total of 52,621 Chinese adults. During the period of 1993–2009, mean BMI values increased by 1.6 kg/m2 among men and 0.8 kg/m2 among women; mean WC values increased by 7.0 cm among men and 4.7 cm among women. The prevalence of overweight increased from 8.0 % to 17.1% among men (P<0.001) and from 10.7% to 14.4% among women (P<0.001); the prevalence of general obesity increased from 2.9% to 11.4% among men (P<0.001) and from 5.0% to 10.1% among women (P<0.001); the prevalence of abdominal obesity increased from 8.5% to 27.8% among men (P<0.001) and from 27.8 % to 45.9 % among women (P<0.001). Similar significant trends were observed in nearly all age groups and regions for both men and women. The prevalence of overweight, general obesity and abdominal obesity among Chinese adults has increased greatly during the past 17 years.
General Obesity, defined by body mass index (BMI), has increased dramatically in China during the past decades (1,2). However, BMI can not provide information on the distribution of body fat (3). Abdominal obesity, as assessed by waist circumference (WC), is more strongly associated with the risk of type 2 diabetes, hypertension, dyslipidemia, cardiovascular disease, cancer, and all-cause mortality than general obesity (4,5). Measurement of WC is usually simple and convenient, requiring little training (6). The US National Institutes of Health recommended that WC be measured to screen for health risk, especially among those with a BMI more than 25.0 kg/m2 (7).
As a developing country, China is presently experiencing rapid economic, social, and cultural changes, including an accelerated pace of nutrition transition that may result in a greatly increased burden of chronic diseases, such as obesity (8). National surveys are necessary to provide updated health information for the development of effective programs and strategies to prevent and control obesity. However, little is known about the recent trends in general and abdominal obesity in Mainland China.
In this study, data from the China Health and Nutrition Surveys (CHNS), a nationally representative cross-sectional health and nutrition survey in China, were used to describe the secular trends in general and abdominal obesity among Chinese adults from 1993 to 2009.
The CHNS is a large-scale, national cross-sectional survey that was designed to explore how the health and nutritional status of the Chinese population has been affected by social and economic changes. Currently, data are available for 1989, 1991, 1993, 1997, 2000, 2004, 2006, and 2009. A multistage, random cluster process was used to draw samples from nine provinces (Liaoning, Heilongjiang, Jiangsu, Shandong, Henan, Hubei, Hunan, Guangxi, and Guizhou). This sample is diverse, with variation found in a wide-range of socioeconomic factors (income, employment, education, and modernization) and other related health, nutritional, and demographic measures (9). All participants provided written informed consent and the study was approved by institutional review board from the University of North Carolina at Chapel Hill and the National Institute for Nutrition and Food Safety, China Center for Disease Control and Prevention.
Participants aged 18 years or older were included in the analysis. Information on age, gender, region, BMI, and WC were collected. There were 8321, 10551, 9688, 9813, 9752, and 10039 participants included in the surveys conducted in 1993, 1997, 2000, 2004, 2006, and 2009, respectively (WC was collected initially from 1993). There were 7760 (93.2%), 8354 (79.2%), 9333 (96.3%), 8983 (91.5%), 8826 (90.5%), and 9365 (93.3%) included in the analyses across the six study periods; incomplete records were due to missing BMI or WC data. The gender distributions across the six survey periods were homogeneous (P=0.486).
Weight was measured to the nearest 0.1 kg with lightweight clothing on a calibrated beam scale and height was measured to the nearest 0.1 cm without shoes using a portable stadiometer. BMI was calculated as weight in kilograms divided by the square of height in meters. WC was measured at a point midway between the lowest rib and the iliac crest in a horizontal plane using non-elastic tape. Height, weight, and WC were measured by trained examiners following a standard protocol from the World Health Organization (WHO) (10). Height, weight, and WC measurements were made at the same location and followed the same protocol at each study visit.
Overweight, general obesity, and abdominal obesity were defined by WHO suggestions for Chinese (overweight: BMI 25 kg/m2 to 27.49 kg/m2; general obesity: BMI ≥ 27.5 kg/m2 (11); abdominal obesity: WC≥90cm for men and ≥ 80cm for women (12)), the criteria recommended by Working Group on Obesity in China (WGOC) (overweight: BMI 24 kg/m2 to 27.99 kg/m2; general obesity: BMI ≥ 28 kg/m2; abdominal obesity: WC≥ 85cm for men and ≥ 80cm for women)(13), and WHO suggestions for Europids (overweight: BMI 25 kg/m2 to 29.99 kg/m2; general obesity: BMI ≥ 30 kg/m2; abdominal obesity: WC ≥102cm for men and ≥ 88cm for women) (14).
SPSS version 13.0 (SPSS, Inc., Chicago, Illinois) was used for data statistical analyses. Trends in BMI, WC, and the prevalence of general and abdominal obesity from 1993 to 2009 were assessed by multiple linear regression or logistical regression models controlling for covariates such as sex, age, and region (15). Since the age distributions across six study periods were greatly different, all survey data (i.e. BMI, WC, and the prevalence of general and abdominal obesity) were standardized to the age distribution of the China Census population in 2000 (16). A P value<0.05 was considered statistically significant.
The summary of previous studies on trends in overweight, general obesity, and abdominal obesity among Chinese adults (1,17–25) are shown in Table 1. During the past decades, the prevalence of overweight, general obesity, and abdominal obesity increased significantly among both men and women in Mainland China. However, the prevalence of those overweight decreased among Chinese women in Beijing, Taiwan and Hong Kong.
Secular changes in mean BMI and WC among Chinese adults from 1993 to 2009 are displayed in Table 2. Overall, both mean BMI and WC values increased significantly across the 6 study periods among both men and women(P<0.001). Averaged BMI values increased by 1.6 kg/m2 in men and 0.8 kg/m2 among women. Mean WC values increased by 7.0 cm among men and 4.7 cm among women. Similar significant trends were observed among all age groups and regions for both men and women (P<0.001). Notably, mean BMI and WC values increased more rapidly among individuals living in rural regions than those residing in urban areas. In addition, both parameters increased more rapidly among men aged 18–59 years, while more rapidly among women over 40 years of age.
The BMI and WC distribution curves between 1993 and 2009 in men and women are shown in Figure 1. Among both men and women, the distribution of higher BMI and WC greatly increased from 1993 to 2009. In addition, men experienced a greater increase in WC than women.
Table 3 shows the trends in prevalence of overweight, general obesity, and abdominal obesity by WHO criteria for Chinese among Chinese adults during the period 1993–2009. The prevalence of those overweight increased from 8.0% to 17.1% among men (P<0.001) and from 10.7% to 14.4% among women (P<0.001); the prevalence of general obesity increased from 2.9% to 11.4% among men (P<0.001) and from 5.0% to 10.1% among women (P<0.001); the prevalence of abdominal obesity increased from 8.5% to 27.8% among men (P<0.001) and from 27.8% to 45.9% among women (P<0.001). In stratified analysis, the prevalence increased over time in each subgroup by age and region for both men and women (P<0.001) with the exception of general overweight among women living in urban regions (P=0.056). Notably, the prevalence of general overweight and obesity and abdominal obesity increased more rapidly among those residing in rural regions. In addition, the two types of obesity increased more rapidly in men aged 18–59 years, while more rapidly among women over 40 years of age. The trends in prevalence of general overweight and obesity and abdominal obesity by WGOC criteria for Chinese and by WHO criteria for Europids among Chinese adults during the period of 1993–2009 are depicted in Supplementary Table 1 and 2.
The present data indicate that mean BMI and WC and the prevalence of overweight, general obesity, and abdominal obesity increased significantly among both men and women in China from 1993 to 2009. Similar trends were observed among nearly all age groups, and in both regions. Notably, the distribution of higher WC greatly increased from 1993 to 2009, especially among men. Additionally, among both men and women, the prevalence of general and abdominal obesity increased more rapidly among individuals aged 40–59 years. The prevalence of general obesity increased more rapidly among men residing in urban areas, while abdominal obesity increased more rapidly among women living in rural regions. Moreover, the abdominal obesity prevalence was alarmingly higher than general obesity, especially among women. These results are of great concern since abdominal obesity assessed by WC is considered to be more closely associated with risk of obesity-related morbidity and mortality (26).
The findings from the current study were consistent with those from the previous studies on general obesity defined by BMI in Mainland China (1,19–21). For instance, the prevalence of general obesity using BMI of 28kg/m2 or more increased from 1.8% to 6.9% among men and 4.1% to 9.0% among women during the period of 1991–2000 (20). In other countries/regions, the patterns of general obesity trends were greatly different (27). General obesity was stable among Chinese men in Hong Kong but declined in women between 1996 and 2005 (23). There was an upward trend in general obesity among adults in Thailand from 1991 to 2004 (28) and Malaysia from 1996 to 2009 (29). Data from the US National Health and Nutrition Examination Survey (NHANES) shows a significantly upward trend among US men but no significant trend among women from 1999 to 2008 (30). By contrast, significantly increasing trends in abdominal obesity were found in other countries although they may vary by sex, age or ethnicity. Abdominal obesity increased significantly among both men and women in the US from 1999 to 2008 (16). Significant trends were observed only among men, but not women in South Korea during the period of 1998–2007 (31). Increasing abdominal obesity among Swedish women is of particular alarm since 1990 (32).
Environmental changes (e.g. increase in energy intake and decrease in physical activity) may account for the major proportion of the increase in general overweight and obesity and abdominal obesity among Chinese adults since it is unlikely that there was a population level genetic shift in the past 17 years. Data from CHNS shows that Chinese food consumption patterns have changed from predominantly rice, wheat and related products to high animal food consumption between 1991 and 2004 (8). It is well documented that gene-environment interactions may better explain human obesity (33). These interactions can also explain the differences in weight gain rates across sex, age and region. Other explanations for the greater increase of abdominal obesity prevalence among men than women might be sex hormone responses to obesogenic environmental changes (31). The increase was larger among subjects between the ages of 40–59 years, which suggests that interventions should prioritize efforts to reduce obesity among this subpopulation (34). It is notable that prevalence of those overweight among women living in urban regions increased from 1993 to 2004 but decreased from 2004 to 2009. The reasons for this decrease are presently unknown and further studies are necessary to explore these reasons. Weight gain among Chinese adults was more rapid between 1993 and 2000, and the rate has since slowed. By contrast, WC increased persistently from 1993 to 2009. These findings suggest a trend in increasing abdominal fat given that mean BMI tends to be somewhat stable. A particular interesting finding is that the prevalence of abdominal obesity increased more rapidly among those living in rural regions. For example, in 1993, the abdominal obesity prevalence by WHO criteria for Chinese was higher among men living in urban areas (12.8%) than those living in rural areas (6.3%), while the differences between the two types of regions diminished in 2009 (urban (27.9%) vs. rural (27.7%)). Economic development and change in diet may help explain the findings. The prevalence of general obesity defined by either WHO criteria or WGOC criteria remained relatively low, while the abdominal obesity diagnosed by each criterion was a major problem among Chinese adults. Studies have revealed that most Asians have a more central distribution of body fat for a given BMI than Europeans (35). The secular trends in mean WC in China over the past 17 years are surprising; the mean WC increased by 7.0 cm among men and 4.7 cm among women. Data from NHANES indicates that each 1 cm increase in WC was associated with approximately a 2%–7% increased odds of hypertension, dyslipidemia and metabolic syndrome. Moreover, the high prevalence of abdominal obesity (37.4 % by WHO criteria and 45.3% by WGOC criteria for Chinese) in 2009 poses a serious public health challenge in China.
This study has several strengths. The sample is nationally representative, even though only nine of China’s 31 provinces were included. The response rate was higher than 90% for all study years, with the exception that it was 79.2% in 1997. Training was conducted for all study staff to ensure standardization of data collection. Vigorous quality assurance and control procedures were employed. This study was, however, subject to several limitations. Social and environmental variables, which would affect obesity, such as education level, family income, dietary habits, sedentary behavior, and physical activity, were not considered. Further studies are necessary to investigate the specific reasons for the observed upward trends in obesity. The results of subgroup analyses should also be interpreted with caution due to limited statistical power.
These results provide new information on the trends of BMI, WC, and the prevalence of overweight, general obesity, and abdominal obesity in China. These health variables increased greatly among nearly all sexes, ages, and regions over the 17 years of the study, with greater increases in abdominal obesity among those living in rural areas. Abdominal obesity appears to be of greater concern than general obesity among Chinese adults. Public health prevention strategies are urgently needed to modify health behaviors in order to reduce abdominal obesity in China and prevent deleterious obesity-related health outcomes (36).
This study was supported by the NIH (R01-HD30880, DK056350, and R01-HD38700), Beijing Health System Leading Talent Grant (2009-1-08) and Beijing Key Science and Technology Program (D111100000611002). We thank the National Institute of Nutrition and Food Safety, China Center for Disease Control and Prevention, Carolina Population Center, the University of North Carolina at Chapel Hill, and the Fogarty International Center for financial support for CHNS data collection and analysis files from 1989 to 2009. We would also like to thank the China-Japan Friendship Hospital and Ministry of Health for support for CHNS 2009 survey.
Conflict of Interests
The authors declare that they have no conflict of interests.