Key Takeaway:
- Vitamin D2 supplementation may lower blood levels of vitamin D3.
- Vitamin D3 generally appears more effective at raising and maintaining vitamin D levels.
- Researchers say more studies are needed to understand the long-term health effects.
Vitamin D2 May Lower Vitamin D3 Levels, researchers say, prompting questions about whether vitamin D3 may be more effective for maintaining vitamin status.
Study Finds Unexpected Vitamin D Interaction
The finding comes from a 2025 systematic review and meta-analysis led by researchers at the University of Surrey, John Innes Centre and Quadram Institute Bioscience. The researchers reviewed 20 studies, with 11 providing data for the main meta-analysis.
Compared with people who did not receive vitamin D2, those taking the supplement had significantly lower concentrations of 25-hydroxyvitamin D3, the main blood marker used to assess vitamin D status. Depending on the analysis, the average reduction ranged from about 9 to 18 nanomoles per liter.
The researchers stressed that the result does not mean vitamin D2 removes vitamin D from the body or that the supplement is inherently harmful. Vitamin D2 also raises its own blood metabolite and can contribute to overall vitamin D status.
Emily Brown, a University of Surrey research fellow and lead researcher, said the study found that vitamin D2 “can actually decrease levels of vitamin D3 in the body,” adding that D3 may be more beneficial for most people, depending on individual circumstances.
D3 Appears More Effective At Raising Vitamin Levels
Vitamin D2, or ergocalciferol, is commonly produced from fungi or yeast, while vitamin D3, or cholecalciferol, is the form the body makes when skin is exposed to sunlight. Both forms can increase vitamin D levels, but evidence indicates D3 generally raises and maintains blood vitamin D more effectively. The findings suggest that Vitamin D2 May Lower Vitamin D3 Levels while still contributing to overall vitamin D status.
A separate 2026 review of 26 randomized controlled trials found that vitamin D2 reduced parathyroid hormone levels and produced a small increase in blood calcium. The findings show that D2 has biological effects and should not be considered ineffective simply because it may reduce circulating D3.
Professor Cathie Martin of the John Innes Centre said the findings highlight the importance of making plant-based vitamin D3 available. Animal-free D3, including products made from lichen, is now available for people seeking non-animal sources.
Researchers Seek Answers On Long-Term Health
Scientists do not yet know why vitamin D2 appears to reduce circulating D3. One proposed explanation is that increasing vitamin D metabolites may activate mechanisms that increase their breakdown and removal from the body.
Earlier research also found differences between D2 and D3 in immune-related gene activity. A study published in Frontiers in Immunology reported that D3, but not D2, stimulated genes associated with type I interferon signaling, an important part of the body’s early immune response.
Professor Colin Smith of the University of Surrey said D3 appeared to stimulate this signaling system, but researchers caution that such findings do not prove that taking D3 prevents infections. More clinical research is needed to determine whether the biochemical differences between the two forms lead to meaningful differences in health outcomes.
For now, researchers say both forms can contribute to vitamin D status, but D3 appears to have an advantage when the goal is raising and sustaining blood vitamin D levels. The study does not establish that everyone should switch supplements, and individual medical needs remain important.
