Background Few studies have examined the impact of weight change in different periods of lifetime on type 2 diabetes risk, and the association of weight loss with type 2 diabetes is unclear. We prospectively investigated the association of weight change since age 20 y and that during middle-to-late adulthood with the incidence of type 2 diabetes.

Methods Subjects were 52 014 men and women aged 45–75 y who participated in the Japan Public Health Center-Based Prospective Study and had no history of diabetes. ORs of self-reported physician-diagnosed type 2 diabetes for weight change between age 20 y and baseline survey (mean age 50.6 y) and during 5 y between baseline and second surveys were estimated using logistic regression analysis.

Results During the 5-year period following 5-year survey, 989 newly diagnosed cases of type 2 diabetes were self-reported. Weight gain from age 20 y was associated with an increased risk of type 2 diabetes. The multivariate-adjusted OR (95% CI) for a weight gain of ≥5 kg versus a stable weight were 2.61 (2.11 to 3.23) in men and 2.56 (1.95 to 3.35) in women. A weight gain of ≥5 kg over the 5-y following the baseline survey was also associated with an increased risk in women. No association with weight loss was observed for either period.

Conclusions These results suggest that long-term weight gain from early adulthood to middle-age increases risk of type 2 diabetes in men and women and that risk is further enhanced by weight gain in later life in women.