Sitting Time and Physical Function in Australian Retirees: An Analysis of Bidirectional Relationships

There is limited evidence on the directionality of the associations of sitting time with physical function. This study examined the longitudinal associations of sitting time with changes in physical function, and physical function with changes in sitting time.

Data from 10,027 retirees in the Social, Economic, and Environmental Factor (SEEF) population-based cohort were collected in 2006-20008 and in 2010-2011. Daily sitting time was assessed by a single-item question. Physical function was measured with the Medical Outcomes Study Physical Functioning Scale (range 0-100) with participants categorized as: no; minor; moderate; or severe limitation. General linear regression models, adjusted for covariates, were used to assess associations of sitting time with physical function for all participants and in subgroups according to sex, and categories of body mass index, physical activity, and physical function limitations.

Each hour of baseline sitting was associated with declines in physical function for women (0.20 units [95% confidence interval {CI} 0.04-0.37]) and those with severe functional limitations (0.65 units [95% CI 0.20-1.12]). Each unit of baseline physical function was associated with declines in sitting time for all participants (0.009 hours/day [95% CI 0.005-0.013]) and for all subgroups.

There was limited evidence of a bidirectional association of sitting time with physical function except in women and people with severe functional limitations. Health promotion efforts are needed to address the impact of poor physical function on increases in sitting time which result in further functional declines for these subgroups of the population.