This study is an extension of an earlier study of vitamin D supplementation conducted on normal weight individuals by Dr. John Aloia of the Bone Mineral Research Division at Winthrop University Hospital. The investigators plan to compare the response to vitamin D supplementation in obese individuals with the response already measured in normal weight individuals. The same dosing schedule of vitamin supplementation will be used as in the past. The doses used in the past have demonstrated safety in a number of trials, here at Winthrop as well as outside of Winthrop Hospital. Sixty study volunteers are planned for enrollment in the study. The study participants will mainly be recruited from a group of patients who have in the past been enrolled in the weight loss program at Winthrop Hospital. Each participant will be on vitamin D supplementation for a total of 8 weeks. Vitamin D blood levels will be measured before and at the end of the supplementation period. They will then be compared to see the change over time as a result of supplementation.

Inclusion Criteria:

• obese adults aged 18-65 years and BMI>35

Exclusion Criteria:

• chronic medical illness (diabetes, malignancy, uncontrolled hypertension, kidney disease)
• subjects who have undergone bariatric surgery or currently enrolled in a medically supervised weight loss program
• BMI < 35
• pregnancy
• use of medication that influences vitamin D metabolism
• history of of hypercalcemia, hypercalciuria, nephrolithiasis