Taking vitamin D2 supplements could actually lower the amount of vitamin D3 in your body, the form that works best. Researchers in the United Kingdom found this surprising effect after analyzing data from multiple clinical trials. The discovery suggests that many people taking the wrong type of vitamin D may be undermining their own health.
Vitamin D2 appears to push down D3 levels
The study, led by scientists at the University of Surrey, the John Innes Centre, and the Quadram Institute Bioscience, looked at results from randomized controlled trials. They found that people who took vitamin D2 supplements ended up with lower concentrations of vitamin D3 in their bodies compared to people who took no D2 at all. In several of the trials, D3 levels actually fell below those of the control groups. This was a previously unknown effect, according to the researchers.
Vitamin D2 and D3 are the two main forms of vitamin D supplements available. The body naturally produces D3 when skin is exposed to sunlight. D3 is also the form that raises overall vitamin D levels most efficiently. The UK government recommends 10 micrograms of vitamin D per day, especially during winter months when sunlight is scarce.
D3 may also help fight viruses and bacteria
A separate study from the same university, published in Frontiers in Immunology, suggests that D3 and D2 do not play identical roles in the immune system. Vitamin D3 appears to stimulate the type I interferon signaling system, which is a key part of the body's first line of defense against viruses and bacteria. D2 did not show the same effect. This means that maintaining healthy D3 levels could help prevent infections from taking hold.
Lead researcher Emily Brown from the University of Surrey said the findings suggest that, subject to personal considerations, vitamin D3 supplements may be more beneficial for most people than vitamin D2. Professor Cathie Martin from the John Innes Centre added that the research highlights the importance of making plant-based vitamin D3 accessible in the UK.
The findings do not mean people should stop taking vitamin D supplements. But they do suggest that choosing the right form matters more than previously understood.
