Variations over four decades in body mass index trajectories prior to diagnosis of diabetes mellitus: The Manitoba Follow-up Study, 1948–2007

OBJECTIVE: The aim of the study was to explore the variations in body mass index (BMI) trajectories during the 20 years before diagnosis of type 2 diabetes mellitus (T2DM) over four decades between 1968 and 2007. METHODS: Longitudinal measurements of BMI from 437 men, all with a diagnosis of T2DM, were used in the analysis. A mixed method approach was used to fit individual patterns of BMI measurements during the 20 years before diagnosis of T2DM. RESULTS: The mean BMI at diagnosis was 26.7 kg/m295% confidence interval, 26.4–27.1). Compared with men whose condition was diagnosed between 1968 and 1977, for men with a diagnosis between 1978 and 2007 the mean BMI about 10 years before diagnosis significantly increased by 0.92 to 1.54 BMI units. Decades also varied in how long there was a persistent increase in BMI during the 20 years before diagnosis. The rate of change in mean BMI among men whose T2DM was diagnosed in the most recent two decades increased by 8.8% to 22.6% during the 10-year interval before diagnosis, but there was no significant difference among men given a diagnosis between 1978 and 1987. The quadratic trend of BMI prior to diagnosis was also significantly affected by age at diagnosis. CONCLUSION: The BMI trajectories during the 20 years leading up to T2DM varied by decade of diagnosis. The increase in BMI persisted for much longer among relatively younger men with a diagnosis in more recent decades. Strategies to prevent T2DM, informed by the pattern of BMI trajectories, should be customized to consider a potential age–period effect. © Canadian Public Health Association, 2015. All rights reserved.