In this large population-based study of community residents living in Zhabei District, Shanghai, approximately one third of the participants had MetS according to the joint interim consensus criteria recently endorsed by a number of national and international organizations . As expected, the prevalence rate was lower when the modified ATPIII criteria were used to define MetS. The prevalence of MetS was slightly higher in men than that in women across all age groups, and increases linearly with age. Similarly, each of the 5 MetS defining metabolic risk factors was highly prevalent and increased with age in this urban Chinese population.
It has been well documented that MetS is highly prevalent world-wide, especially in affluent countries [14–16]. Several previous studies have reported the prevalence of MetS in Chinese population using various criteria [11, 17, 18]. The report by Gu et al. based on a national survey of Chinese adults aged 35–74 years conducted in 2000–2001 reported that the age-standardized prevalence of MetS was only 9.8% in men and 17.8% in women according to the NCEP ATP III criteria, and 15.1% (13.6% in men and 16.6% in women) using the modified NCEP ATP III criteria . Another survey of 16,442 adults (aged ≥18 years) conducted between August and October 2005 in Beijing reported prevalence of 23.2% and 16.2% using the IDF and NCEP ATP III criteria, respectively . Another study of 5,584 adults (age = 20–79 years) conducted in 2008 in Pudong New Area, a relatively affluent business district in Shanghai, reported prevalence of 28.4% for men and 35.1% for women using the modified NCEP ATP III criteria . In the Shanghai Men’s Health Study by Villegas R et al., the prevalence rate for men aged 40–74 years was 29.34% according to the modified NCEP ATP III criteria for Asian populations . Our present study based on a large representative sample of urban community residents in Zhabei District of Shanghai, a traditionally industrialized district of Shanghai, used the currently recommended gender-specific waist circumference cut-off points for Chinese and showed high prevalence of MetS comparable to that reported in Pudong New Area. For direct comparison, estimated age-standardized (to Shanghai 2009 census counts) prevalence of MetS among those aged 35–74 years in our study using the modified NCEP ATP III definition was 21.6% (23.7% in men and 19.4% in women), which was still considerably higher than that reported by Gu et al. Although the two surveys differed in the study design and the targeted populations sampled, the higher prevalence of MetS in our study conducted in 2009–2010 in Zhabei District of Shanghai, in conjunction with the higher prevalence reported in the study conducted in 2008 in Pudong New Area of Shanghai, as compared to the study by Gu et al. conducted in 2000–2001 may truly indicate a rapidly rising trend of MetS in a short 8–9 year span, especially among urban Chinese population. In support of this, several recent studies have also reported substantial increase of overweight/obesity and overt diabetes in China [3, 20, 21].
Insulin resistance is believed to be the underlying core mechanistic feature of metabolic syndrome. Obesity, abdominal adiposity in particular, plays an important role in the pathogenesis of insulin resistance and metabolic syndrome. An increasing number of comparative studies showed that at given BMIs, metabolic responses were greater in Asians as compared to Caucasians or US blacks, supporting the endorsement of ethnicity- and gender-specific cut-off points of waist for central obesity in the consensus definition of MetS [22–25]. A study comparing data from the National Health and Nutrition Survey (NHANES) III in US and from the Nutrition and Health Survey in Taiwan further showed that Chinese experienced much higher risk of hypertension, hyperglycemia, dyslipidemia, and hyperuricemia than US whites and blacks at given BMIs . This discrepancy is likely due to a higher percentage of central body fat accumulation in Asians than in Caucasians at fixed BMIs [23, 26, 27]. In our study, even among the 1,564 men with a waist circumference of larger than 85 cm (consensus cut-off point for central obesity) but less than 90 cm (modified NCEP ATP III cut-off point), the other 4 MetS defining metabolic abnormalities are highly prevalent: 1,025 (65.5%) having elevated blood pressure or hypertension, 654 (41.8%) having hypertriglyceridemia, 526 (33.0%) having elevated fasting glucose or diabetes, and 273 (17.0%) having low HDL-C. Thus, the use of the consensus criteria with Chinese specific cut-off points for abdominal obesity is a sensible measure of the true burden of MetS in China.
The MetS is known to significantly increase the risks of diabetes and cardiovascular diseases. Even after excluding those with a known diagnosis of diabetes or CHD, the prevalence of MetS was still as high as 29.1% in our study population. At present, there is no national screening program for metabolic risk factors in China. Thus, it is conceivable that an alarmingly high proportion of the general adult urban population in China currently asymptomatic and without known diagnosis of diabetes mellitus or CHD has undiagnosed MetS and is not optimally managed for their metabolic abnormalities. These persons are at great risk of progressing to full-blown type 2 diabetes mellitus and of developing cardiovascular diseases. Indeed, a recent study has shown that the prevalence of diabetes has tripled in the recent decades in China . Accumulating evidence also indicates that obesity and MetS significantly increase the risks of many cancers . With the widespread urbanization and westernization following China’s rapid economic growth, there is no sign of abating of upward trend of obesity and MetS. Unchecked, it will certainly further increase the burden of type 2 diabetes mellitus and other chronic diseases in China.
There are a few limitations in our study. First, the completion rate of our study was modest at 63.0%, which could to some extent have limited the generalizability of our study results. However, comparison of age and gender distribution between the respondents and the non-respondents showed no statistically significant differences, supporting that our study sample is a good representation of the source population. Second, a cardinal feature of MetS is insulin resistance or glucose intolerance. We did not perform glucose tolerance test or directly measure circulating levels of insulin or C-peptide in this study; as such, some participants with impaired glucose tolerance but normal fasting glucose levels could have been misclassified. Nevertheless, elevated fasting glucose level is a commonly accepted criterion to define MetS.