Impact of Vitamin D on 25-hydroxyvitamin D Levels and Physical Function

Dose for intervention arm is 800 IU/day for first 4 months. At 4 months, if vitamin D level \<70 nmol/L, a second 800 IU capsule will be added to regimen (total of 1600 IU/d) for remainder of study.

Those in the placebo group will receive 1 capsule for first 4 months. At 4 month visit, one capsule will be added to regimen to be taken throughout the remainder of the study.