[A prospective study on body mass index and mortality].

OBJECTIVE: To assess the relationship between body mass index (BMI, weight in kilograms divided by the square of height in meters) and both all-causes mortality and mortality from specific cause.

METHODS: Cardiovascular disease (CVD) risk factors were studied in 1982 - 1985 on more than 30 thousands participants aged 35 - 59 from 10 Chinese populations. 30 560 participants (15 723 for men, 148 837 for women) without known myocardial infraction, stroke or cancer was followed from 1999 to 2000. All-causes of death were documented.

RESULTS: Three thousand two hundred and twelve death cases occurred during follow-up of average 15.2 years, including 676 CVD (coronary heart disease and stroke) deaths, 1 281 cancer deaths and 1 255 deaths for other reasons. Cox proportional hazards model adjusting age and gender showed that the relative risks of all causes of death in groups of low BMI (BMI < 18.5), normal BMI (BMI from 18.5 to 23.9), overweight (BMI from 24 to 27.9) and obesity (BMI >/= 28) which were defined according to the strata of BMI for Chinese were 1.21 (95% CI: 1.10 - 1.33), 1.00, 0.91 (95% CI: 0.82 - 1.01) and 1.12 (95% CI: 0.93 - 1.37), respectively ("U" shaped relation). The relative risk of low BMI group (RR = 1.01, 95% CI: 0.84 - 1.21) was not significant different and the relative risk of obesity significantly increased (RR = 1.36, 95% CI: 1.04 - 1.80) while the lowest relative risk was in normal BMI group. The relative risks increased for CVD death, but decreased for cancer death with increased levels of BMI and a "U" shaped relationship was found between BMI groups and mortality for other reasons, which remained after excluding the early death and smokers.

CONCLUSION: BMI in normal level was not only related to low risk of all causes of death, but also with relative low risk of CVD, cancer and other deaths. Data were important to public health.