Tejal SomvanshiA 2025 meta-analysis of randomized controlled trials found that vitamin D2 supplements were associated with lower circulating levels of vitamin D3. The research challenges the assumption that vitamin D2 and D3 are interchangeable.
What the study found
Researchers from the University of Surrey, John Innes Centre and Quadram Institute Bioscience reviewed 20 studies for the systematic review and meta-analysis, published in Nutrition Reviews in 2025. Eleven studies provided data for the main meta-analysis.
The analysis found that vitamin D2 supplementation was associated with a statistically significant reduction in serum 25-hydroxyvitamin D3 compared with control or placebo. Depending on the analysis, the average reduction was about 9 to 18 nmol/L.
What it means for supplement users
Consumers taking vitamin D supplements should check the label to see whether the product contains vitamin D2, also called ergocalciferol, or vitamin D3, also called cholecalciferol. Anyone considering a change should discuss it with a pharmacist, doctor or registered dietitian, particularly if they take medication or have a health condition.
Which form is better?
*Is Vitamin D3 better than Vitamin D2?* Research consistently finds that vitamin D3 is more effective than vitamin D2 at raising and sustaining total 25-hydroxyvitamin D levels in the blood. The new meta-analysis also found that D2 supplementation can reduce circulating D3 levels.
The study does not establish that vitamin D2 is unsafe or that people should stop taking prescribed supplements. Vitamin D2 still contributes to overall vitamin D status.
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