A review of clinical research published in Nutrition Reviews found that supplementation with vitamin D2 may reduce vitamin D3 levels in the body, compared to not taking vitamin D3 supplements. These findings highlight concerns that vitamin D2 may have unfavorable effects on immunity, especially in comparison to vitamin D3. The study was conducted by researchers from the University of Surrey, John Innes Center, and Quadram Institute Bioscience.

“Vitamin D supplements are important, especially between October and March, when our bodies cannot make vitamin D from sunlight in the U.K.,” said Emily Brown, PhD, research fellow and lead researcher of the study. “However, we discovered that vitamin D2 supplements can actually decrease levels of vitamin D3 in the body, which is a previously unknown effect of taking these supplements. This study suggests that subject ot personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2.”

“This meta-analysis highlights the importance of ensuring plant-based vitamin D3 is accessible in the U.K.,” said Cathie Martin, professor and group leader at the John Innes Center.

The research supports a previous study published in Frontiers in Immunology, published by Colin Smith, professor at the University of Surrey, which suggests that vitamins D2 and D3 don’t have identical roles in immune function. That’s because D3 possesses specific immune-modulating properties not found in D2.

“We have shown that vitamin D3, but not vitamin D2, appears to stimulate the type I interferon signaling system in the body — a key part of the immune system that provides a first line of defense against bacteria and viruses. Thus, a healthy vitamin D3 status may help prevent viruses and bacteria from gaining a foothold in the body,” Smith said.

Further research is needed to distinguish the different functionalities of vitamins D2 and D3 to help individuals decide which of the two vitamins should be a priority.

“Vitamin D deficiency represents a significant public health concern, especially during the winter months, with significant deficiency across the UK population,” said Martin Warren, professor and chief scientific officer at the Quadram Institute. “This collaborative research effort aligns well with the Quadram Institute’s mission to deliver healthier lives through food innovation to enhance the nutrient density of the food we eat. Tackling this with the most effective form of vitamin D supplementation or fortification is of the utmost importance to the health of the nation.”