Background: The association between body mass index (BMI) and mortality among Asian diabetic people, especially with respect to the obesity paradox (ie, higher BMI is associated with lower mortality risk), remains unresolved. Methods: We followed a cohort of 3851 self-reported Japanese diabetics (2115 men and 1736 women) in the Japan Collaborative Cohort Study from 1988-1990 through 2009. Individuals were aged 40 to 79 years and free from a history of cardiovascular disease, cancer, renal disease, or tuberculosis. BMI was grouped into the following four categories: <20.0, 20.0-22.9, 23.0-24.9, and ≥25.0 kg/m2. Results: During 54 707 person-years of follow-up, 1457 deaths from all causes, 445 from cardiovascular disease, 421 from cancer, 43 from renal disease, and 148 from infectious disease were documented. Mortality from all causes, cardiovascular disease, cancer, and renal disease showed L-shaped associations with BMI. Compared to diabetics with BMI of 20.0-22.9 kg/m2, those with BMIs of 23.0-24.9 kg/m2 and ≥25.0 kg/m2 had lower risks of mortality from infectious disease (ie, obesity paradox). The multivariable HRs for mortality from infectious disease were 0.50 (95% confidence interval, 0.31-0.81) and 0.51 (95% confidence interval, 0.32-0.82) among participants with BMIs of 23.0-24.9 kg/m2 and ≥25.0 kg/m2, respectively. Similar results were observed after stratification by smoking status and age and exclusion of early deaths. Conclusions: We observed L-shaped associations between BMI and mortality from all causes, cardiovascular disease, cancer, and renal disease, while the association between BMI and mortality from infectious disease manifested the obesity paradox.
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