A body mass index over 22 kg/m2 at college age is a risk factor for future diabetes in Japanese men.

Background: There is a high incidence of type 2 diabetes in Asian adults, even those with a normal body mass index (BMI) (<25.0 kg/m2). For example, it has been shown that a slightly increased BMI (>23 kg/m2) at middle age is a risk factor for type 2 diabetes in Asians. In this historical cohort study, we investigated whether a slightly increased BMI at college age was also a risk factor for future diabetes in Japanese men.

Methods: Six hundred and sixty-one male alumni who graduated from a physical education school between 1971 and 1991 and who responded to follow-up investigation between 2007 and 2017 were included in this study. Participants were categorized into four categories: college BMI of <21.0 kg/m2, 21.0-22.0 kg/m2, 22.0-23.0 kg/m2, and ≥23.0 kg/m2, and the incidence and risk ratio of diabetes were compared between groups.

Results: The median follow-up period was 32 years (interquartile range, IQR: 27-36), which included 20,983 person-years of observation. Subjects were 22 (22-22) years old at college graduation, and 55 (50-59) years old at the final follow-up investigation. During the study period, 56 men developed diabetes; the prevalence rates for the lowest to highest BMI categories were 4.4%, 7.6%, 10.5%, and 11.3%, respectively, and their adjusted hazard ratios were 1.00 (reference), 1.77 (95% CI: 0.68-4.30), 2.42 (1.00-5.84), and 2.53 (1.06-6.07), respectively (p = 0.03 for trend).

Conclusion: Our data suggest that a BMI over 22.0 kg/m2 at college age is a risk factor for diabetes later in life in Japanese men.