Which Vitamin D Supplement Boosts Levels More — D₂ or D₃?

In the U.S., vitamin D supplements are available over-the-counter as D₃ (cholecalciferol; usually in 400–1000 IU doses) and by prescription as vitamin D₂ (ergocalciferol; Drisdol and others; often prescribed at 50,000 IU doses). In previous research, D₃ supplements raised blood levels of 25-hydroxyvitamin D (25[OH]D) more than D₂ did at equivalent doses. In two new studies, researchers reach the same conclusion.

In a randomized trial, 64 older adults received daily D₂ or D₃ (1600 IU) or monthly D₂ or D₃ (50,000 IU). Mean 25(OH)D levels were about 33 ng/mL at baseline. At 1 year, mean 25(OH)D levels had increased by 9 ng/mL in both the daily and monthly D₃ groups; mean levels increased by 6 and 4 ng/mL in the daily and monthly D₂ groups, resp…