[Effect of the combination of "weight gain of more than 10 kg since age 20" and obesity on the new onset of diabetes mellitus].

Objective　Few reports have examined the association between "weight gain since the past combined with the presence of obesity" and diabetes mellitus (DM). Therefore, we longitudinally examined the influence of the combination of "weight gain of ≥10 kg since the age of 20 years" and the presence of obesity on the new onset of DM.Methods　We identified 8,704 National Health Insurance enrollees in Habikino City, Osaka Prefecture, who underwent specific health checkups in 2013. After excluding those who had DM previously and those who were untraceable and had missing data, 5,708 participants were included in the analysis. The risk of the new onset of DM was classified into "no weight gain/non-obese," "no weight gain/obese," "weight gain/non-obese," and "weight gain/obese" groups. Weight gain and obesity were defined as gaining ≥10 kg since the age of 20 based on responses to a standard questionnaire from the Ministry of Health, Labour and Welfare and a BMI ≥25 kg/m². A Cox proportional hazards model was used to examine the risk of the new onset of DM.Results　Participants' mean age was 64.3 ± 7.9 years. During the mean follow-up period of 3.14 ± 1.13 years, 126 (6.0%) men and 133 (3.7%) women developed DM. The hazard ratios (95% confidence interval [CI]) for the new onset of DM were significantly higher in the weight gain/non-obese (1.77 [95% CI: 1.26-2.49]) and weight gain/obese groups (2.76 [95% CI: 2.05-3.72]), with the no weight gain/non-obese group as the reference group. By sex, the hazard ratio for men in the weight gain/obese group was 2.06 (95% CI: 1.34-3.18), whereas the hazard ratio was higher for women in the weight gain/obese (3.68 [95% CI: 2.44-5.53]) and weight gain/non-obese groups (2.19 [95% CI: 1.35-3.55]).Conclusion　Weight gain was a risk factor for the development of DM in individuals without obesity. This factor was more pronounced in women, who had a higher risk of the new onset of DM if they had gained > 10 kg since the age of 20, even if their BMI was less than 25 kg/m². The results suggest that those who fall into this category should receive lifestyle improvement guidance, even if they are not eligible for specific health guidance.