Context Two reports suggested that vitamin D₂ is less effective than vitamin D₃ in maintaining vitamin D status.

Objective Determine whether vitamin D₂ was less effective than vitamin D₃ in maintaining serum 25-hydroxyvitamin D levels or increased the catabolism of 25-hydroxyvitamin D₃.

Subjects and Design This was a randomized, placebo-controlled, double-blinded study of healthy adults ages 18–84 years who received either placebo, 1,000 IU of vitamin D₃, 1,000 IU of vitamin D₂, or 500 IU of vitamin D₂ plus 500 IU of vitamin D₃ daily for 11 weeks at the end of the winter.

Results Sixty percent of the healthy adults were vitamin D deficient at the start of the study. The circulating levels of 25-hydroxyvitamin D (mean ± SD) increased to the same extent in the groups that received 1,000 IU daily as vitamin D₂ (baseline 16.9 ± 10.5 ng/ml; 11 weeks 26.8 ± 9.6 ng/ml); vitamin D₃ (baseline 19.6 ± 11.1 ng/ml; 11 weeks 28.9 ± 11.0 ng/ml) or a combination of 500 IU vitamin D₂ and 500 IU vitamin D₃, (baseline 20.2 ± 10.4 ng/ml; 11 weeks 28.4 ± 7.7 ng/ml). The 25-hydroxyvitamin D₃ levels did not change in the group that received 1,000 IU vitamin D₂ daily. 1,000 IU of vitamin D₂ or vitamin D₃ did not raise 25-hydroxyvitamin D levels in vitamin D deficient subjects above 30 ng/ml.

Conclusion 1,000 IU of vitamin D₂ daily was as effective as 1,000 IU of vitamin D₃ in maintaining serum 25-hydroxyvitamin D levels and did not negatively influence serum 25-hydroxyvitamin D₃ levels. Therefore, vitamin D₂ is equally as effective as vitamin D₃ in maintaining 25-hydroxyvitamin D status.