China Kadoorie Biobank of 0.5 million people: survey methods, baseline characteristics and long-term follow-up

Abstract

Background: Large blood-based prospective studies can provide reliable assessment of the complex interplay of lifestyle, environmental and genetic factors as determinants of chronic disease.

Methods: The baseline survey of the China Kadoorie Biobank took place during 2004-08 in 10 geographically defined regions, with collection of questionnaire data, physical measurements and blood samples. Subsequently, a re-survey of 25,000 randomly selected participants was done (80% responded) using the same methods as in the baseline. All participants are being followed for cause-specific mortality and morbidity, and for any hospital admission through linkages with registries and health insurance (HI) databases.

Results: Overall, 512,891 adults aged 30-79 years were recruited, including 41% men, 56% from rural areas and mean age was 52 years. The prevalence of ever-regular smoking was 74% in men and 3% in women. The mean blood pressure was 132/79 mmHg in men and 130/77 mmHg in women. The mean body mass index (BMI) was 23.4 kg/m(2) in men and 23.8 kg/m(2) in women, with only 4% being obese (>30 kg/m(2)), and 3.2% being diabetic. Blood collection was successful in 99.98% and the mean delay from sample collection to processing was 10.6 h. For each of the main baseline variables, there is good reproducibility but large heterogeneity by age, sex and study area. By 1 January 2011, over 10,000 deaths had been recorded, with 91% of surviving participants already linked to HI databases.

Conclusion: This established large biobank will be a rich and powerful resource for investigating genetic and non-genetic causes of many common chronic diseases in the Chinese population.

Figure 1

Locations of the 10 survey sites and number recruited. Open circles indicate rural areas and solid circles indicate urban areas. Number recruited at baseline in each area is shown in brackets

Figure 2

Proportion of participants born in each calendar year. Open bars indicate people born during these years were eligible for only part of the 4-year recruitment period at baseline survey due to age restriction. The effects of the 1959–61 famine vary by site. The small numbers of participants born before 1930 or after 1973 are shown as 1930 or 1973, respectively

Figure 3

Variation of selected baseline variables across 10 study areas. Adjusted for age and for male and female combined results, additional adjustment was also made for sex. (a) Overall: per cent with ≥6 years education; (b) men: per cent ever-regular smokers, (c) men: per cent drinking alcohol weekly, (d) men: per cent drinking tea regularly; (e) overall: per cent consuming dairy food regularly; (f) overall: per cent eating spicy food regularly; (g) overall: per cent taking food supplements; (h) overall: per cent using smoky cooking fuel; (i) overall: per cent obese; (j) women (65–74 years): per cent with five or more live births; (k) women (35–44 years): per cent using oral contraceptives; and (l) overall: per cent with diabetes reported. Open bars indicate rural areas and grey bars indicate urban areas

Figure 4

Prevalence of selected baseline variables by sex and by age or year of birth. Adjusted for area. (a) Overall: per cent with ≥6 years education; (b) overall: per cent married with spouse; (c) overall: per cent ever-regular smokers; (d) overall: per cent drinking alcohol weekly; (e) overall: per cent drinking tea regularly; (f) overall: per cent consuming dairy food regularly; (g) overall: per cent taking food supplements; (h) women: per cent with age at menarche <13 years; and (i) women: per cent with five or more live births

Figure 5

Associations of different measures of adiposity with self-reported diabetes at baseline. Prevalence of diabetes vs (a) BMI, (b) waist circumference, (c) waist/hip ratio, (d) body fat percentage after adjustment for age and area. Solid boxes denote men and open boxes denote women. Vertical line indicates 95% confidence interval (CI)