Background and purpose: Although overweight is an important risk factor for cardiovascular disease in Western countries, the impact of overweight has not been well elucidated in Japan, where its prevalence is low.
Methods: A total of 104,928 Japanese (43,889 men and 61,039 women) aged 40 to 79 years, free of stroke, coronary heart disease, and cancer at entry participated in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk Sponsored by Monbusho (JACC Study) between 1988 and 1990. Systematic surveillance was completed until the end of 1999, with 1,042,835 person years of follow-up, and the underlying causes of death were determined based on the International Classification of Diseases.
Results: There were 765 total strokes (191 intraparenchymal hemorrhages), 379 coronary heart diseases, and 1707 total cardiovascular diseases for men; and for women, there were 685 (145), 256, and 1432, respectively. Compared with persons with body mass index (BMI) 23.0 to 24.9, those with BMI > or =27.0 kg/m2 had a higher risk of coronary heart disease; for men and women, the respective multivariate relative risk (95% CI) was 2.05 (1.35 to 3.13) and 1.58 (0.95 to 2.62). Persons with BMI <18.5 kg/m2 had higher risk of total stroke and intraparenchymal hemorrhage, for men and women, the respective multivariate relative risk was 1.29 (1.01 to 1.49) and 1.92 (1.49 to 2.47) for total stroke and 1.96 (1.16 to 3.31) and 2.32 (1.36 to 3.97) for intraparenchymal hemorrhage. These excess risks did not alter materially when deaths within 5 years were excluded or when smoking status was taken into account.
Conclusions: For Japanese men and women, high BMI was associated with increased risk of coronary heart disease, whereas low BMI was associated with intraparenchymal hemorrhage.