This study is a 12-month, double-blind randomized placebo controlled trial in older (65-89 yrs) men and women with initial 25(OH)D concentrations of 18-<30 ng/mL to determine the effect of increasing 25(OH)D concentrations to ≥30 ng/mL through vitamin D3 supplementation on 1) change in neuromuscular functions that are established risk-factors for falls in older adults; and 2) changes in the underlying physiological mechanisms over 4 months in a subset of randomly selected participants. Participants will be randomized to 2000 IU/d of vitamin D3 or placebo. Lower extremity muscle strength and power, physical performance, and postural sway will be assessed at baseline, 4 months and 12 months and falls assessed monthly. Muscle biopsies of the vastus lateralis will be taken at baseline and 4 months to assess muscle fiber type, contractility, and denervation, and number and differentiation stage of satellite cells.
The purpose of this study is to see if vitamin D supplementation improves muscle function in older adults.