Participants will be withdrawn from the study if serum 25(OH)D levels are identified as within the deficient range so that the patient can receive needed treatment. A vitamin D deficiency will be defined as 25(OH)D concentrations less than 20 ng/mL (50 nmol/L) and vitamin D insufficiency as 21 to 29 ng/mL. In addition, if an abnormally high level of 25(OH)D is obtained (200 ng/mL or 500 nmol/L), we will have the 25(OH)D measurement repeated. If the second test is confirmed to be high, then we will withdraw that particular patient from the study for medical follow-up. If we find a trend of excess vitamin D among participants, however, we will re-evaluate and consider termination of the study.