Inclusion Criteria:

- Nonsmoking men and women, ages 18-65

- Body mass index (BMI) ≥ 28 kg/m² and within 10% of maximum weight

- Serum 25(OH)D level ≤ 20 ng/ml

- Serum insulin level ≥ 7.2 mU/l

- Willingness to maintain current body weight for the duration of the study

- Willingness to maintain baseline lifestyle activities and routines for the duration
of the study

- Willingness to avoid the use of non-steroidal anti-inflammatory drugs (NSAIDS),
including low-dose daily aspirin, for at least ten days prior to each admission (due
to the potential effects of these agents on inflammatory markers.)

- Willingness to avoid the use of all over-the-counter or prescription vitamins,
dietary supplements, and herbal products during the study, with the exception of a
basic multivitamin supplement.

- If of childbearing potential, willingness to use highly effective contraception for
the duration of the study.

Exclusion Criteria:

- Current tobacco smoking

- History of bleeding or coagulation disorders

- Gastrointestinal disease resulting in significant gastrointestinal dysfunction or
malabsorption

- History of diabetes, or diagnosed during screening OGTT

- Current treatment with hypertensive medications

- History of cardiovascular disease

- Renal disease, as evidenced by a serum creatinine above the upper limit of normal on
more than one screening visit

- History of kidney stones

- History of chronic hepatitis, or liver enzymes (AST or ALT) more than 2.5 times the
upper limit of normal

- Primary hyperparathyroidism or baseline hypercalcemia from any cause

- Current treatment with over-the-counter or prescription weight loss medications, such
as orlistat or sibutramine

- History of bariatric surgery

- Current treatment with any cholesterol-lowering medications, such as statins, niacin,
fibrates, or ezetimibe

- Blood pressure ≥ 145/90 after ten minutes of rest on more than one screen visit

- Hyperthyroidism or untreated hypothyroidism. Subjects with chronic, treated, stable
hypothyroidism may be included in the study at the discretion of the Principal
Investigator.

- Pregnancy, desired pregnancy, or lactation within the study period.

- HIV, Hepatitis B and C

- Medical conditions requiring daily calcium supplementation or antacid use

- Use of medications known to interact with calcium or vitamin D metabolism
(bisphosphonates, corticosteroids, thiazide diuretics, cholestyramine, colestipol,
mineral oil, phenytoin, barbituates, dititalis glycosides, antacids)

- Subjects with known hypersensitivity to cholecalciferol

- Participation in an investigational drug study within one month of screening

- History, physical, or laboratory findings suggestive of any other medical or
psychological condition that would, in the opinion of the principal investigator,
make the candidate ineligible for the study