Adiposity and diabetes in China: the China Kadoorie Biobank study of 500,000 men and women

Thesis

Despite the rapid increase in both adiposity and diabetes in China, substantial uncertainty remains about the relationship between these two conditions in the population. Using data from the China Kadoorie Biobank study of 0.5 million adults recruited during 2004-8 from 10 diverse areas of China, this thesis examines the associations of different adiposity measures (overall adiposity: BMI and percentage body fat; central adiposity: waist circumference, waist-hip ratio, and waist-height ratio) with type 2 diabetes prevalence and incidence. To assess the quality of diagnosis, a separate event-verification study was conducted in ~1,000 reported diabetes cases.

Overall at baseline, the mean age of the analysed participants was 52 years, 41% were men, 32% had a BMI≥25 kg/m² (4% ≥30 kg/m²) and 5.2% had self-reported or screen-detected diabetes. Both cross-sectional and prospective analyses of well-characterised diabetic cases (26,622 prevalent and 2,910 incident cases) showed that adiposity is strongly positively associated with diabetes (p<0.0001), throughout all or most of the distribution of each adiposity measure. Per 1 SD higher adiposity measure, measures of central adiposity were associated with ~90% increased risk, compared with ~80-85% increased risk for general adiposity measures. Among measures of central adiposity, waist-hip ratio was the most strongly associated with diabetes prevalence, whereas waist circumference was the most predictive of diabetes incidence. Although measures of central adiposity were the most strongly associated with diabetes risk, there was still a strong positive association with measures of general adiposity after adjusting for central adiposity (p<0.0001), and the combination of both types of measure improved risk prediction. Given waist circumference, hip circumference was inversely associated with both diabetes prevalence and incidence (p<0.0001). For many of the above associations, there was possible effect modification by age and sex. These findings will provide important and reliable evidence to quantify the level of diabetic risk associated with adiposity, hence to inform clinical interventional strategies and future public health programmes.

Authors: Tang, K

• Publication date: 2014
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Medical Sciences; Epidemiology