Study Finds Vitamin D2 May Lower Vitamin D3 Levels

A 2025 research review found that vitamin D2 supplements were associated with lower levels of vitamin D3, the version the body makes after sunlight reaches the skin. D3 is also generally better at raising and sustaining the blood measurement used to assess vitamin D status. Both forms can increase total vitamin D, so the finding does not mean D2 removes the nutrient or is automatically harmful.

The review combined evidence from 20 studies, including 11 used for its main analysis. People taking D2 had about 9 to 18 fewer nanomoles per liter of the D3-related blood marker, depending on the analysis. Researchers from the University of Surrey, John Innes Centre and Quadram Institute Bioscience said the reason for the difference is still unclear. One possibility is that the body speeds up the processing of existing vitamin D compounds when another form rises.

Earlier research also found that D2 and D3 may affect immune-related gene activity differently. D3 was linked with activity involving type I interferon signaling, part of the body's early response to viruses and bacteria. That result shows a biological difference, but it does not establish that D3 prevents any particular infection. Animal-free D3 made from lichen is available for people seeking a plant-based source.