A Randomized Controlled Trial of the Effects of Vitamin D on Muscle Strength and Mobility in Older Women with Vitamin D Insufficiency

OBJECTIVES: To evaluate the effects of vitamin D treatment on muscle strength and mobility in older women with vitamin D insufficiency. DESIGN: One‐year population‐based, double‐blind, randomized, controlled trial. SETTING: Perth, Australia (latitude 32°S). PARTICIPANTS: Three hundred two community‐dwelling ambulant elderly women aged 70 to 90 with a serum 25‐hydroxyvitamin D (25(OH)D) concentration less than 24 ng/mL. INTERVENTION: Vitamin D 2 1,000 IU/d or identical placebo; calcium citrate (1 g calcium/d) in both groups. MEASUREMENTS: Lower limb muscle strength and mobility as assessed using the Timed Up and Go Test (TUAG). RESULTS: At baseline, mean±standard deviation serum 25(OH)D was 17.7±4.2 ng/mL; this increased to 24.0±5.6 ng/mL in the vitamin D group after 1 year but remained the same in the placebo group. For hip extensor and adductor strength and TUAG, but not for other muscle groups, a significant interaction between treatment group and baseline values was noted. In those with baseline values in the lowest tertile, vitamin D improved muscle strength and TUAG more than calcium alone (mean (standard error): hip extensors 22.6% (9.5%); hip adductors 13.5% (6.7%), TUAG 17.5% (7.6%), P <.05). Baseline 25(OH)D levels did not influence patient response to supplementation. CONCLUSION: Vitamin D therapy was observed to increase muscle function in those who were the weakest and slowest at baseline. Vitamin D should be given to people with insufficiency or deficiency to improve muscle strength and mobility.