Adiposity and risks of colorectal and small intestine cancer in Chinese adults: a prospective study of 0.5 million people.

BACKGROUND: Uncertainty remains about the associations of adiposity with intestinal cancer in China and by its anatomical subtype. METHODS: The prospective China Kadoorie Biobank recorded 3024 incident cases of colorectal (CRC) and 143 cases of small intestine (SIC) cancer during a 10-year follow-up among 509 568 participants without prior cancer at baseline. Cox regression was used to estimate adjusted hazard ratios (HRs) for specific cancers associated with adiposity. RESULTS: Overall mean body mass index (BMI) was 23.7 kg/m2. BMI was positively associated with CRC (HR per SD 1.10 [95% CI 1.06-1.14]), colon (1.13 [1.07-1.18]), and rectal (1.07 [1.02-1.13]) cancer. For waist circumference, the corresponding HRs per SD were 1.14 (1.10-1.18), 1.18 (1.13-1.24), and 1.11 (1.05-1.16), respectively. The adjusted HRs were somewhat greater in men than women. Adiposity was positively, but non-significantly, associated with SIC risk. CONCLUSIONS: Among relatively lean Chinese adults, adiposity was associated with risks of colon and rectal cancer, with the associations somewhat stronger in men than women.

Physical activity and sedentary leisure time and their associations with BMI, waist circumference, and percentage body fat in 0.5 million adults: the China Kadoorie Biobank study.

BACKGROUND: Few large studies in China have investigated total physical activity and sedentary leisure time and their associations with adiposity. OBJECTIVE: We investigated determinants of physical activity and sedentary leisure time and their associations with adiposity in China. DESIGN: A total of 466,605 generally healthy participants (age: 30-79 y, 60% female) in the China Kadoorie Biobank were included in this cross-sectional analysis. Self-reported information on a range of activities was collected by interviewer-administered questionnaire. Physical activity was calculated as metabolic equivalent task hours per day (MET-h/d) spent on work, transportation, housework, and nonsedentary recreation. Sedentary leisure time was quantified as hours per day. Adiposity measures included BMI, waist circumference, and percentage body fat (by bioimpedance analysis). Associations were estimated by linear and logistic regression. RESULTS: The mean physical activity was 22 MET-h/d, and the mean sedentary leisure time was 3.0 h/d. For each sex, physical activity was about one-third lower among professionals/administrators than among factory workers, with intermediate levels for other occupational categories. A 1-SD (14 MET-h/d) greater physical activity was associated with a 0.15-unit (95% CI: 0.14, 0.16) lower BMI (in kg/m(2)), a 0.58-cm (95% CI: 0.55, 0.61) smaller waist circumference, and 0.48 (95% CI: 0.45, 0.50) percentage points less body fat. In contrast, a 1-SD (1.5 h/d) greater sedentary leisure time was associated with a 0.19-unit higher BMI (95% CI: 0.18, 0.20), a 0.57-cm larger waist circumference (95% CI: 0.54, 0.59), and 0.44 (95% CI: 0.42, 0.46) percentage points more body fat. For any given physical activity level, greater sedentary leisure time was associated with a greater prevalence of increased BMI, as was lower physical activity for any given sedentary leisure time. CONCLUSIONS: In adult Chinese, physical activity varies substantially by occupation, and lack of physical activity and excess sedentary leisure time are independently and jointly associated with greater adiposity.