Trajectories of body mass index among Canadian seniors and associated mortality risk.

BACKGROUND: This study aims to characterize the heterogeneity in BMI trajectories and evaluate how different BMI trajectories predict mortality risk in Canadian seniors.

METHODS: Data came from the Canadian National Population Health Survey (NPHS, 1994-2011) and 1480 individuals aged 65-79 years with at least four BMI records were included in this study. Group-based trajectory model was used to identify distinct subgroups of longitudinal trajectories of BMI measured over 19 years for men and women. Cox proportional hazards models were used to examine the association between BMI trajectories and mortality risks.

RESULTS: Distinct trajectory patterns were found for men and women: 'Normal Weight-Down'(N-D), 'Overweight-Normal weight' (OV-N), 'Obese I-Down' (OB I-D), and 'Obese II- Down' (OB II-D) for women; and 'Normal Weight-Down' (N-D), 'Overweight-Normal weight' (OV-N), 'Overweight-Stable' (OV-S), and 'Obese-Stable' (OB-S) for men. Comparing with OV-N, men in the OV-S group had the lowest mortality risk followed by the N-D (HR = 1.66) and OB-S (HR = 1.98) groups, after adjusting for covariates. Compared with OV-N, women in the OB II-D group with three or more chronic health conditions had higher mortality risk (HR = 1.61); however, women in OB II-D had lower risk (HR = 0.56) if they had less than three conditions.

CONCLUSION: The course of BMI over time in Canadian seniors appears to follow one of four different patterns depending on gender. The findings suggest that men who were overweight at age 65 and lost weight over time had the lowest mortality risk. Interestingly, obese women with decreasing BMI have different mortality risks, depending on their chronic health conditions. The findings provide new insights concerning the associations between BMI and mortality risk.