Longitudinal associations of serum 25-hydroxyvitamin-D, physical activity, and knee pain and dysfunction with muscle loss in community-dwelling older adults

Aim: To describe the associations of between-person and within-person variability in serum 25-hydroxyvitamin D (25(OH)D), physical activity (PA) and knee pain and dysfunction with muscle mass, strength and muscle quality over 10 years in community-dwelling older adults.

Method: Participants (N = 1033; 51% women; mean age 63 ± 7.4 years) were measured at baseline, 2.5, 5, and 10 years. Lower limb lean mass (LLM) was assessed using dual energy X-ray absorptiometry, lower limb muscle strength (LMS) using a dynamometer, and lower limb muscle quality (LMQ) calculated as LMS/LLM. Knee pain and dysfunction were assessed using the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index. PA was measured using pedometers. Linear-mixed effect regression models, with adjustment for confounders, were used to estimate the association of within-person and between-person variability in PA, 25(OH)D, and WOMAC scores with muscle mass, strength, and muscle quality.

Results: Both between-person and within-person increases in PA were associated with LLM, LMS and LMQ (all P < 0.05). Within-person and between-person increases in knee pain and dysfunction were associated with LLS and LMQ but not LLM (all P < 0.05). Between-person effects showed that higher average 25(OH)D was associated with higher 10-year average LLM, LMS and LMQ (all P < 0.05); whereas, within person increases in average 25(OH)D was associated with a higher LMS, LMQ but not LLM.

Conclusions: Variability in 25(OH)D, pain and dysfunction within an individual over time relate to muscle changes in that individual. Increasing one's own physical activity level further increases muscle mass, strength and quality supporting the clinical recommendation of promoting PA to reduce age-related muscle loss.