Increasing trends in central obesity among Chinese adults with normal body mass index, 1993-2009

Background: Central obesity is thought to be more pathogenic than overall obesity and studies have shown that the association between waist circumference (WC) and mortality was strongest in those with a normal body mass index (BMI). The objective of our study was to determine secular trends in the prevalence of central obesity (WC >= 90 cm for men and >= 80 cm for women) among Chinese adults with normal BMI from 1993 to 2009 and to examine the impact of performance of combined BMI and WC on the prevalence of obesity in Chinese adults. Methods: We used data from the China Health and Nutrition Survey (CHNS) conducted from 1993 to 2009. From which we included a total of 52023 participants aged >= 18 years. Results: The age-standardized prevalence of central obesity among Chinese adults with BMI < 25 kg/m(2) increased from 11.9% in 1993 to 21.1% in 2009 (P for linear trend < 0.001). The upward trends were noted in both genders, all ages, rural/urban settings, and education groups (all P for linear trend < 0.001), with greater increments in men, participants aged 18-64 years, and rural residents (P for interaction terms survey x sex, survey x age, and survey x rural/urban settings were 0.042, 0.003, and < 0.001, respectively). Trends in the prevalence of central obesity were similar when a more stringent BMI < 23 kg/m(2) cut point (Asian cut point) was applied. Central obesity is associated with a higher risk of incident hypertension within normal BMI category. More than 65% individuals with obesity would be missed if solely BMI was measured. Conclusions: We observed an upward trend in the prevalence of central obesity among participants with normal BMI irrespective of sex, age, rural/urban settings, and education level. Central obesity is associated with a higher risk of incident hypertension within normal BMI category. Approximately two thirds of the individuals with obesity would be missed if WC was not measured. It is, therefore, urgent to emphasize the importance of WC as a measure to monitor the prevalence of obesity.