Under- and overweight impact on mortality among middle-aged Japanese men and women: a 10-y follow-up of JPHC Study cohort I

OBJECTIVE: Although obesity is a major health problem in Western countries, its impact may differ in another culture. This paper examines the association between body mass index (BMI; kg/m(2)) and mortality in Japan, where the mortality profile and BMI distribution differ substantially from Western countries. DESIGN: The JPHC Study cohort 1, a population-based prospective study in four public health center areas, started in 1990 and was followed-up to the end of 1999. SUBJECTS: A total of 19 500 men and 21 315 women aged 40 - 59 y who submitted their body weight and height and did not report any serious disease at baseline. MEASUREMENT: Risk of death by category of BMI, RESULTS: During 10 y of follow-up, 943 and 483 deaths were documented in the men and women, respectively. The association between BMI and all-cause mortality was U-shaped: compared with a category of 23.0-24.9, the statistically significant elevations in relative risk were observed in both under-and overweight categories (2.26 in 14.0-18.9, 1.57 in 19.0-20.9, 1.33 in 21.0-22.9 and 1.38 in 27.0-29.9, 1.97 in 30.0-39.9 in men, 1.94 in 14.0-18.9 and 1.91 in 30.0-39.9 in women) after adjustment for possible confounders and weight change. The U-shaped association did not change after excluding deaths occurring in the first 5y of follow-up or even after excluding subjects who reported a weight loss of 5 kg or more since 20-y-old, or after stratifying subjects by smoking status. CONCLUSION: Both under- and overweight are important determinants of premature death among the Japanese population.