Age modify the associations of obesity, physical activity, vision and grip strength with functional mobility in Irish aged 50 and older

Objective: To estimate whether the associations of obesity, physical activity, vision and grip strength with functional mobility were modified by age. Methods: Data from The Irish Longitudinal Study on Ageing (2009-2012) were analyzed and 5001 individuals were included in this study. Mobility was assessed by the timed up and go test (TUG-test). Main exposure variables were obesity, physical activity, visual acuity and grip strength at baseline. Multiple linear regression models were fitted to assess the associations of baseline main exposure variables with 2-year follow-up functional mobility and potential confounders were adjusted. Stratified analyses by age were used to assess the interaction between main exposures and age on functional mobility. Results: Multiple linear regression models identified significant interactions of obesity (P < 0.001), vigorous physical activity (P = 0.001), vision (P < 0.001) and grip strength (P < 0.001) with age on functional mobility. Stratified analyses suggested that the risk effect of obesity on functional mobility was greater in middle-aged group (beta = 0.025, P < 0.001) than in older group (beta = 0.016, P = 0.017). The protective effects of high level of physical activity and grip strength on functional mobility were stronger in older group (beta = - 0.023, P = 0.004 for physical activity; beta = - 0.002, P < 0.001 for grip strength) than in middle-aged group (beta = - 0.012, P = 0.008 for physical activity; beta = - 0.0015, P < 0.001 for grip strength). The benefit of better vision on functional mobility was observed in middle-aged group only (beta = - 0.032, P = 0.002). Conclusion: Non-obesity, higher level of physical activity, vision and grip strength at baseline were associated with better mobility performance among middle-aged and older Irish. And these associations were modified by age.