[A prospective cohort study on body mass index and mortality among middle-aged and elderly men in urban Shanghai].

OBJECTIVE: To examine the association between body mass index (BMI) and mortality as well as the effect of age on it among middle-aged and elderly men in urban area of Shanghai.

METHODS: A total of 18,244 male subjects aged 45-64 years resided in urban area of Shanghai were enrolled in the study during January 1, 1986 through September 30, 1989, and were actively followed under annual visits. 'Cox proportional hazards model' was used to estimate the relative risks (RR).

RESULTS: By the end of the follow-up process in 2002, a total number of 235,762 person-years was accumulated in the cohort, with an average of 12.9 years per subject. A total number of 3365 deaths including 1381 from cancer and 1165 from cardio- and cerebro-vascular diseases (CVD), was identified during the follow-up period. Compared with those under normal BMI (BMI 18.5-23.9), the RRs of death for all causes of death among groups at low BMI (BMI < 18.5), overweight (BMI 24-27.9) and obesity (BMI > or = 28) were 1.20, 1.12 and 1.61, respectively, among non-smokers after adjustment for age, alcohol consumption and level of education. After excluding the numbers observed during the first 5 years of follow-up, the corresponding RRs became 1.01, 1.12, and 1.75, respectively. The risk of deaths from colon cancer or CVD increased along with the increase of BMI, while the risk of non-cancer and non-CVD deaths, mostly deaths from infectious diseases, increased significantly in the group of low BMI. Among those aged > or = 55 years at baseline survey, the risk for all causes of death increased more significantly with those having obesity. However, among those who were younger than 55 years of age, no significant correlation between BMI and overall mortality was noticed.

CONCLUSION: A positive relationship between obesity and total mortality was observed in the middle-aged and elderly men in urban Shanghai. The association was more obvious among the elderly while the risk of deaths from colon cancer or CVD rose along with the increase of BMI. The risk of death from infectious disease increased significantly in the group with low BMI.