New research from the University of Surrey, the John Innes Center and the Quadrum Institute for Biosciences suggests that taking vitamin D2 can reduce your body’s levels of vitamin D3, the more efficient form of vitamin D. Many people take vitamin D supplements to support bone and immune health, particularly during the winter months, to meet the UK government’s recommendation of 10 micrograms (μg) daily.
There are two forms of vitamin D supplements available: vitamin D2 and vitamin D3. Researchers have found that taking vitamin D2 supplements can reduce vitamin D3 levels in the body. Vitamin D3 is the vitamin D3 that our bodies naturally produce from sunlight and is most effectively used to boost overall vitamin D levels.
This research nutrition reviewsanalyzed data from a randomized controlled trial and found that taking vitamin D2 supplements lowered vitamin D3 levels compared to people who did not take vitamin D2 supplements. In many studies, vitamin D3 levels were lower than in the control group.
Emily Brown, PhD and Research Fellow in the Department of Nutrition, Kinesiology, Chronobiology and Sleep at the University of Surrey, said:
“Vitamin D supplements are important in the UK, especially between October and March, when our bodies are unable to produce vitamin D from sunlight, so in the UK we found that vitamin D2 supplements can actually reduce vitamin D3 levels in the body. This is a previously unknown effect of taking these supplements. This study suggests that vitamin D3 supplements may be more beneficial than vitamin D2 for most people, subject to personal considerations.”
Professor Cathy Martin, group leader at the John Innes Centre, said:
“This meta-analysis highlights the importance of ensuring the availability of plant-based vitamin D3 in the UK.”
The study supports previous research published in Frontiers in Immunology, led by Professor Colin Smith from the University of Surrey, suggesting that vitamins D2 and D3 do not have the same role in supporting immune function. Vitamin D3 has a modifying effect on the immune system and may strengthen the body against viral and bacterial diseases.
Professor Colin Smith said:
“We showed that vitamin D3, but not vitamin D2, appears to stimulate the body’s type I interferon signaling system, a key part of the immune system that is the first line of defense against bacteria and viruses. Therefore, when vitamin D3 is healthy, it may help prevent viruses and bacteria from entering the body.”
Depending on individual requirements, further research into the different functions of vitamins D2 and D3 should be prioritized when deciding whether to make vitamin D3 the first choice of vitamin D supplements.
Professor Martin Warren, Chief Scientific Officer of the Quadrum Institute, said:
“Vitamin D deficiency represents a significant public health concern, particularly during the winter months when vitamin D deficiency is acute across the UK. This collaborative research effort aligns well with the Quadram Institute’s mission to provide healthier lives through food innovations that increase the nutrient density of the foods we eat. Tackling this problem with the most effective forms of vitamin D supplementation or fortification is of paramount importance to the health of the nation.”

