Low vs. Moderate to High Dose Vitamin D for Prevention of COVID-19

Subjects are able to participate if they: 1. Are 18 years or older. 2. Live or work in the Chicagloland area (Illinois counties: Cook, Lake, McHenry, DuPage, Kane, Kendall, Grundy, Will, and Kankakee; Indiana counties: Lake and Porter). 3. Are interested in vitamin D as a potential preventive measure against COVID-19 in which they self-administer a daily dose of vitamin D during the 9-month study period. 4. Are willing to attend the laboratory for drop-in appointments at UChicago Medicine or Rush University Medical Center every 3 months at 4 time points over a 9-month period for blood draws measuring COVID-19 antibodies, calcium, vitamin D and PTH levels. 5. Are willing to complete self-report measures at 4 time points over the course of 9 months by completing a 15-minute survey at intake by telephone or via web and 10-minute web-based follow-up surveys. Subjects are excluded from study participation if they: 1. Report ever having a positive COVID-19 PCR test result 2. Report being pregnant, planning to become pregnant, and/or report breastfeeding during the study period. 3. Report a history of chronic kidney disease, including a history of abnormal GFR and/or creatinine. 4. Report a history of hyperparathyroidism. 5. Report a history of increased falls. 6. Report a history of hypercalcemia. 7. Report a history of gastrointestinal absorptive disorders, including having undergone bariatric surgery. 8. Report a history of kidney stones (1 in past year or 2 in lifetime). 9. R…