Linear and non-linear associations between physical activity, body composition and multimorbidity over 10 years among community-dwelling older adults.

BACKGROUND This study aims to describe the relationships between physical activity (PA), body composition and multimorbidity over 10 years. METHODS Participants (N=373; 49% women; average age 61.3±6.7 years) were followed for 10 years. Multimorbidity was defined by self-report as the presence of two or more of 12 listed chronic conditions. PA (steps-per-day) at baseline was assessed by pedometer, handgrip strength (HGS) by dynamometer and appendicular lean mass (ALM) and total body fat mass by dual x-ray absorptiometry . Relative HGS and ALM were calculated by dividing each body mass index (BMI). Regression cubic splines were used to assess evidence for a non-linear relationship. RESULTS After 10 years, 45% participants had multimorbidity. There was a non-linear relationship between PA and multimorbidity - PA was associated with lower multimorbidity risk among individuals who engaged in <10,000 steps-per-day (RR=0.91, 95% CI: 0.85, 0.97, per 1000 steps-per-day), but not among those who participated in ≥10,000 steps-per-day (RR=1.04, 95% CI: 0.93, 1.09, per 1000 steps-per-day). Higher BMI (RR=1.05, 95% CI: 1.02, 1.08, per kg/m 2) and fat mass (RR=1.03, 95% CI: 1.01, 1.04, per kg), and lower relative HGS (RR=0.85, 95% CI: 0.77, 0.94, per 0.1 psi/kg/m 2) and ALM (RR=0.93, 95% CI: 0.88, 0.98, per 0.1 kg/kg/m 2) were linearly associated with a higher risk of multimorbidity. Absolute HGS and ALM were not significantly associated with multimorbidity. DISCUSSION These findings highlight the potential clinical importance of maintaining adequate levels of PA and of reducing adiposity and maintaining muscle function for minimising the risk of multimorbidity in older adults.