Vitamin D insufficiency, which is prevalent in older individuals, is associated with bone and muscle weakness and falls. Objective: We examined the effects of a weekly dose of 8400 IU vitamin D 3 on postural stability, muscle strength, and safety. Design: In this double-blind trial, subjects aged 70 y with serum 25-hydroxyvitamin D [25(OH)D] concentrations 20 but 6 ng/ mL were randomly assigned to receive a weekly dose of 8400 IU vitamin D 3 (n = 114) or a placebo (n = 112). Mediolateral body

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... ay with eyes open (assessed with the AccuSway PLUS platform; Advanced Medical Technology Inc, Watertown, MA) was the primary endpoint. Secondary endpoints included the short physical performance battery (SPPB) and serum 25(OH)D concentrations. An analysis of covariance model was used for treatment comparisons. Safety and tolerability were monitored. Results: Serum 25(OH)D concentrations rose significantly (from 13.9 to 26.2 ng/mL, P , 0.001) in patients treated with 8400 IU vitamin D 3 but not in patients treated with the placebo. After 16 wk, neither mediolateral sway nor SPPB differed significantly between treatment groups. However, in the post hoc analysis of patients subgrouped by baseline sway (0.46 compared with ,0.46 cm), treatment with 8400 IU vitamin D 3 significantly reduced sway compared with treatment with placebo (P = 0.047) in patients with elevated baseline sway but not in patients with normal baseline sway. Adverse experiences and incidences of hypercalcemia, hypercalciuria, and elevated creatinine were similar with both treatments. In patients treated with 8400 IU vitamin D 3 , but not in placebotreated patients, parathyroid hormone decreased significantly. Conclusions: Weekly treatment with 8400 IU vitamin D 3 raised 25(OH)D concentrations in elderly, vitamin D-insufficient individuals. Treatment with 8400 IU vitamin D 3 did not reduce mediolateral sway significantly compared with treatment with placebo in this population, although in post hoc analysis, treatment with 8400 IU vitamin D 3 reduced sway in the subgroup of patients who had elevated sway at baseline. Weekly treatment with 8400 IU vitamin D 3 was well tolerated. This trial was registered at clinicaltrials.gov as NCT00242476. Am J Clin Nutr 2010;91:985-91.