The Pittsburgh Vitamin D Study: Vitamin D Supplementation in Vitamin D-deficient Subjects at Risk of Lung Cancer

Inclusion Criteria:

1. Age ≥ 50 years old.
2. Current or ex-smoker with at least 10 pack-year history
3. COPD, GOLD II or greater (defined as FEV1/FVC \<70% and FEV1 % predicted \<80%)
4. 25(OH)D3 level ≤25 ng/mL
5. Willingness to comply with study guidelines.
6. Willingness to avoid alternative/additional vitamin D3 supplementation for the duration of the trial
7. Participant must understand the investigational nature of this study and sign an Independent Ethics Committee/Institutional Review Board approved written informed consent form prior to receiving any study related procedure.

Exclusion Criteria:

1. Personal history of lung cancer or head and neck cancer
2. History of malabsorption syndrome (e.g., pancreatic insufficiency, celiac disease, or tropical sprue).
3. History of known thyroid disease
4. History of known sarcoid disease
5. History of known abnormalities in calcium metabolism
6. Hypercalcemia (serum calcium in excess of laboratory ULN)
7. Self-reported consumption of more than 4 alcoholic drinks per day
8. Use of anti-seizure medications phenobarbital or phenytoin, which can disrupt vitamin D metabolism
9. History of known renal dysfunction
10. History of known nephrolithiasis (kidney stones)
11. Current participation in another cancer chemoprevention study
12. Any condition which in the Investigator's opinion deems the subject an unsuitable candidate to receive study drug.
13. Inability to swallow pills.
14. Vitamin D supplementation \> 2,000 IU/day of vitamin D within 30 days prior to enrollment.
15. Being pregnant