Exclusion Criteria:Subjects will be excluded if they have evidence of vitamin D deficiency (< 20 ng/mL), hypercalcemia (calcium > 2.63 mmol/L), hypocalcemia (calcium < 1.75 mmol/L), renal insufficiency (GFR < 50 ml/min), or a history of primary hyperparathyroidism or renal tubular acidosis.Participants will be excluded if they take medications that interfere with vitamin D metabolism, have significant sun exposure, plan to travel to sunny climates during the study, or a history of hypercalcemia.