Linear and nonlinear 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. Method: 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 2 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-energy 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 nonlinear relationship. Results: After 10 years, 45% participants had multimorbidity. There was a nonlinear relationship between PA and multimorbidity - PA was associated with lower multimorbidity risk among individuals who engaged in <10 000 steps/d (relative risk [RR] = 0.91, 95% CI: 0.85, 0.97, per 1 000 steps/d), but not among those who participated in ≥10 000 steps/d (RR = 1.04, 95% CI: 0.93, 1.09, per 1 000 steps/d). Higher BMI (RR = 1.05, 95% CI: 1.02, 1.08, per kg/m2) 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/m2) and ALM (RR = 0.93, 95% CI: 0.88, 0.98, per 0.1 kg/kg/m2) 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 minimizing the risk of multimorbidity in older adults.