Vitamin D2 supplements may reduce the body's vitamin D3 levels
New research suggests that vitamin D2 supplements can reduce circulating levels of vitamin D3, the form the skin makes after sun exposure. Evidence indicates D3 is better at raising and sustaining blood vitamin D and may support immune defenses more strongly than D2. The findings challenge the idea that the two supplement types are interchangeable.
The 2025 review, led by University of Surrey with John Innes Centre and Quadram Institute Bioscience, pooled randomized trial evidence. It examined 20 studies, though only 11 yielded data for the main meta-analysis. When compared with participants not given vitamin D2, those receiving it showed notably lower 25-hydroxyvitamin D3. Depending on analysis, the average drop was about 9–18 nmol/L.
Vitamin D2 (ergocalciferol) usually comes from UV-treated fungi or yeast, while D3 (cholecalciferol) matches what skin makes after UVB exposure. D3 supplements may use sheep-wool lanolin or lichen-derived animal-free sources. The liver turns either form into 25-hydroxyvitamin D, the blood-test marker; D2 yields the D2 version, D3 yields the D3 version.
This finding could affect people who use vitamin D2 supplements, especially those choosing it for dietary or manufacturing reasons, and the clinicians advising them. It may encourage clearer label information and more discussion about which form best supports blood levels. Supplement makers might reconsider formulations, while consumers could become more attentive to D2 versus D3. Because the evidence concerns a biomarker, not proven clinical outcomes, any practical impact may depend on further research and individual guidance.