A growing body of evidence suggests that vitamin D status is important in biologic processes involved in the maintenance of physical function. To advance the investigators understanding of the role of vitamin D in physical function, the investigators will conduct a feasibility pilot study to collect key information to help design a full-scale randomized trial to determine whether vitamin D supplementation will delay declines in physical function. The primary goals of the pilot study are to determine cost-effective strategies for identifying persons at high risk for functional decline with insufficient vitamin D levels, determine the serum vitamin D response to a vitamin D supplementation regimen designed to attain sufficient vitamin D levels, and provide preliminary data of key functional measures (balance, physical performance and muscle power) for the future larger study design. A secondary goal is to begin to examine potential mechanisms by which vitamin D supplementation may enhance physical performance by exploring the effects of vitamin D supplementation on changes in skeletal muscle gene expression.