Body weight and mortality: a prospective evaluation in a cohort of middle-aged men in Shanghai, China

Background The relationship between relative body weight and mortality has been well studied in Western populations and remains controversial. Little is known about the weight-mortality association in less well fed people in developing countries. Methods A cohort of 18 244 Chinese men aged 45-64 years in Shanghai, China enrolled in a prospective study of diet and cancer during January 1986 through September 1989. At recruitment, height and usual body weight were collected through interview. An active, annual follow-up of the cohort was conducted for cancer and death. Proportional hazards regression method was used to examine the relation between body mass index (BMI, weight in kg/height in m(2)) and overall and cause-specific mortality. Results By 28 February 1995, 1198 deaths (498 from cancer, 422 from cardio- and cerebrovascular disease, and 278 from other causes) had been identified. We found a U-shaped relation between BMI and total mortality among lifelong non-smokers, Compared with non-smokers with BMI 21.0-<23.5, the relative risk (RR) for all cause mortality was 1.73 (95% confidence interval [CI]:1.23-2.42) for men with BMI <18.5 and 1.48 (95% CI:1.07-2.03) for men with BMI greater than or equal to 26 after adjustment for age, level of education, and alcohol drinking. The elevated risk of death in men with BMI greater than or equal to 226 was largely due to fatal cardio- and cerebro-vascular diseases. There was a nearly twofold excess risk of death from cardio- and cerebrovascular diseases among lifelong non-smokers with BMI greater than or equal to 26 compared with non-smokers with BMI 21-<23.5 (95% CI: 1.17-3.22). On the other hand, the increased overall mortality risk in men with BMI <18.5 was primarily due to causes of an infectious origin. Exclusion of the first 4 years of follow-up data did not materially alter the BMI-mortality associations. Conclusion Underweight and overweight both are associated with an increased risk of death in middle-aged Chinese men who never smoked cigarettes. The increased total mortality in overweight men is largely due to cardio- and cerebro-vascular diseases while the elevated risk of death in underweight men is attributed primarily to causes of an infectious nature.