Changes in waist circumference relative to body mass index in Chinese adults, 1993–2009

BACKGROUND: Although BMI and waist circumference (WC) are correlated, the relationship between WC and BMI may have changed over time. OBJECTIVES: Describe temporal trends in BMI and WC distributions and quantify the increase in WC at a given BMI over time. SUBJECTS/METHODS: Data on adults aged 20–59 years from two waves (1993 and 2009) of the China Health and Nutrition Survey (CHNS) were used in a pooled cross-sectional analysis. Quantile regression examined age-adjusted temporal trends in the distributions of BMI and WC. Linear regression examined changes in mean WC over time, adjusting for BMI, age at survey and survey year. All models were stratified by gender. RESULTS: There was a significant increase in BMI and WC over time, particularly at the 95(th) quantile: on average, men had 2.8 kg/m(2) (95% CI: 2.4, 3.3) and women 1.5 kg/m(2) (95% CI: 1.1, 2.0) higher BMI in 2009 compared to their counterparts in 1993. WC increased by 9.0 cm (95% CI: 7.5, 10.1) and 5.0 cm (95% CI: 3.4, 6.6) for and women had a 3.2 cm (95% CI: 2.8, 3.7) and 2.1 cm (95% CI: 1.7, 2.5) higher WC in 2009 compared to their counterparts in 1993, holding BMI and age constant. WC adjusted for BMI increased to a larger extent amongst obese versus lean individuals and amongst younger versus older women. CONCLUSIONS: For both genders, BMI and WC increased significantly over time, with particularly greatest increase in magnitude in the upper tail of the BMI and WC distributions. Furthermore, WC at equivalent BMI was higher in 2009, compared to their counterparts in 1993. Our findings suggest that even if BMI remained constant from 1993 to 2009, adults in 2009 might be at increased cardiometabolic risk as a result of their higher WC.