Changes in body mass index and incidence of diabetes: A longitudinal study of Alberta's Tomorrow Project Cohort

Although obesity is a known risk factor for diabetes, the impact of body mass index (BMI) changes over time, especially BMI reduction, on diabetes development is less than clear. The objective of this study is to characterize the association between BMI changes over time and incidence of diabetes in a cohort of adults in Alberta. From 2000 to 2008, Alberta's Tomorrow Project (ATP) enrolled participants aged 35-69 to a population-based prospective cohort study. BMI was calculated from self-reported height and weight; change in BMI (Delta BMI) was calculated as the difference between baseline and follow-up measurements. Diabetes cases were identified using the Canadian National Diabetes Surveillance System algorithm applied to linked administrative data (2000-2015). Multivariable Cox regression was used to examine the association between Delta BMI and incidence of diabetes. In a subset of the ATP cohort (n = 19,164), 1168 incident cases of diabetes were identified during 198,853 person-years of follow-up. Overall, BMI increase was associated with increased risk and BMI reduction was associated with reduced risk of diabetes. Particularly, compared to minimal BMI change (+/- 5%), moderate (5%-10%) reduction in BMI was associated with 34% (95% CI: 12%-51%) reduction in risk of diabetes in participants with obesity; whereas 10% or greater increase in BMI was associated with an increased risk of diabetes of 64% or more in participants with overweight and obesity; in participants with normal and underweight, BMI changes was not apparently associated with risk of diabetes. Public health programs promoting weight loss, even at a moderate extent, would reduce risk of diabetes.