Causal effects of physical activity and sedentary behaviour on health deficits accumulation in older adults.

Abstract

Background: Increasing physical activity (PA) and reducing sedentary behaviour (SB) have been associated with healthy ageing, but their effects when adjusted for reverse causation and selection bias remain unclear. Methods: A deficits accumulation (DA) index based on the number and severity of 51 health deficits (0-100%) was calculated at baseline and three biannual follow-up visits, in a representative cohort of 3 228 community-dwelling older adults in Spain. Average differences in DA index by previous recreational PA, household PA, mentally-active SB and passive SB were estimated using marginal structural models with inverse probability of exposure and censoring weights. Results: Compared with participants with previous recreational PA of 10-19.9 metabolic equivalent hours/week (MET-hours/week), average differences in DA index (95% confidence intervals) were 0.19 (-1.09, 1.48), 0.69 (-0.23, 1.61), -0.66 (-1.34, 0.02), -0.87 (-1.59, -0.13) and -0.55 (-1.37, 0.28) for 0, 0.1-9.9, 20-29.9, 30-39.9 and ≥40 MET-hours/week, respectively (P for trend = 0.006). Household PA showed no effect on subsequent DA after adjusting for reverse causation. Women, but not men, who spent 7-14.9, 15-20.9 and ≥21 h/week on mentally active SB had DA decreases of 0.09 (-1.00, 1.19), 1.08 (-0.28, 2.45) and 2.17 (0.58, 3.75), respectively, compared with 1-6.9 h/week (P for trend = 0.005); whereas women who spent 3-3.9, 4-4.9 and ≥5 h/day on passive SB showed DA increases of 0.41 (-0.52, 1.35), 1.35 (0.13, 2.57) and 2.13 (0.78, 3.47), respectively, compared with 2-2.9 h/day (P for trend = 0.001). Conclusions: The proposed methodology allows estimation of the causal effects of PA and SB on ageing, by simulating a random assignment in which all subjects have the same probability of exposure.