Study finds plant-based vitamin D2 may lower bodily D3 levels, researchers warn

A meta-analysis of randomized controlled trials published in Nutrition Reviews found that supplements containing vitamin D2 were associated with declines in circulating vitamin D3 levels, prompting calls from researchers for greater access to plant-based vitamin D3 and closer attention to the form of vitamin D people take.

Researchers led by Dr. Emily Brown at the University of Surrey analyzed data from multiple trials and concluded that vitamin D3—the form the body produces in response to sunlight and that is found in animal-source foods such as oily fish, egg yolks and liver—was the most efficient at boosting overall vitamin D status. In contrast, the investigators reported that taking vitamin D2 supplements, which are commonly added to fortified foods because they are cheaper to produce, was linked with reductions in vitamin D3 concentrations compared with control groups that did not receive supplementation.

"We discovered that vitamin D2 supplements can actually decrease levels of vitamin D3 in the body, which is a previously unknown effect," Dr. Brown said. She added that "subject to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2."

The analysis, which the authors described as a meta-analysis of randomized controlled trials, builds on earlier research indicating that the two forms of vitamin D are metabolized differently. Professor Colin Smith of the University of Surrey, whose earlier work the current study supports, has said vitamin D3 appears to have effects on the immune system that vitamin D2 does not replicate.

Researchers and public health experts said the findings have implications for supplementation and food fortification policies. Professor Cathie Martin of the John Innes Centre, a co-author on the paper, said the study "highlights the importance of ensuring plant-based vitamin D3 is accessible in the UK." Professor Martin Warren of the Quadram Institute said the work aligns with efforts to improve nutrient density and called addressing deficiency "of the utmost importance to the health of the nation."

Vitamin D, often called the "sunshine vitamin," helps the body absorb calcium and plays roles in bone, muscle and immune function. Health authorities such as the U.K. National Health Service recommend that people consider supplementing with vitamin D during months with limited sunlight. Current guidance equates recommended intake with around 10 micrograms a day, and warns against taking more than 100 micrograms daily unless advised by a doctor because excessive intake can lead to hypercalcaemia, a condition that can damage the kidneys and heart.

Public-health data cited by the authors and other experts indicate that vitamin D insufficiency is common. Estimates in the study and accompanying commentary said roughly one in six adults in the U.K. do not get enough vitamin D, and that during winter months as many as two in five adults may be deficient.

The study's authors and other clinicians also drew cautionary links between vitamin D status and broader health outcomes while noting the evidence is not definitive. Professor Smith suggested that a healthy vitamin D3 status may help the body resist infection, and oncologist Dr. Justin Stebbing has previously proposed that vitamin D might have a role in reducing the risk of bowel cancer, though he and others acknowledged the vitamin’s exact role in cancer prevention remains unclear.

Medical professionals responding to the study urged people to consider the form of vitamin D they take and to consult health-care providers about appropriate supplementation, particularly for those following strict plant-based diets or who rely on fortified foods. The authors said further research could help clarify mechanisms by which D2 appears to lower D3 and inform fortification strategies.

Until regulators or health bodies revise guidance, people are advised to follow existing recommendations on dosage and to seek medical advice if they have concerns about deficiency or are considering higher-dose supplements.