The investigators have recently observed that among healthy women age 65 and older who participated in a placebo-controlled vitamin D and calcium intervention trial, those treated with supplements had a lower risk of falling than those in the placebo group. Vitamin D receptors (VDRs) are present in muscle tissue and are thought to mediate the favorable effects of vitamin D on muscle performance. Vitamin D insufficiency is common particularly in the elderly and supplementation with a relatively high dose of vitamin D may be a useful approach for improving muscle performance and potentially lowering the risk of falling in sedentary older women and other high-risk populations.~The investigators will aim to study women, age 65 and older, with 25(OH)D levels below 60 nmol/l in a double-blind, 4-month randomized controlled pilot study. Eligible subjects will be randomized to treatment with 4000 IU per day of vitamin D3 or placebo. Blood and 24 hour urine will be measured at the beginning and end of the study as outlined in the intervention and measurement schedule below. In addition, a safety random spot urine will be analyzed for calcium and creatinine on day 30. Muscle performance measures will be measured and muscle biopsies will be performed at the beginning and end of the study.
The purpose of the study is to investigate the effect of vitamin D on muscle tissue and physical performance.