Taking vitamin D2 supplements may be counterproductive, according to new research from the University of Surrey, John Innes Centre, and Quadram Institute Bioscience. Scientists discovered that vitamin D2 supplementation can reduce the body's concentration of vitamin D3, the form your body naturally produces from sunlight and uses most efficiently to boost overall vitamin D levels.

What's the Difference Between Vitamin D2 and D3?

Most people know vitamin D is important for bone and immune health, but fewer realize there are two distinct forms available as supplements. When you're exposed to sunlight, your body naturally produces vitamin D3. Vitamin D2, by contrast, is typically derived from plant sources and fungi. Both are available as over-the-counter supplements, but the new research suggests they don't work equally in your body.

The study, published in Nutrition Reviews and analyzing data from randomized controlled trials, found that taking vitamin D2 supplements led to a measurable drop in vitamin D3 levels compared to people not taking vitamin D2 supplements. In many of the studies reviewed, vitamin D3 levels in the D2 supplement group actually fell below those in the control group.

"Vitamin D supplements are important, especially between October and March, when our bodies cannot make vitamin D from sunlight in the UK. 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," said Emily Brown, PhD Research Fellow and Lead Researcher of the study from the University of Surrey's Nutrition, Exercise, Chronobiology and Sleep Discipline.

Emily Brown, PhD Research Fellow and Lead Researcher, University of Surrey

Why Does This Matter for Your Immune System?

The distinction between D2 and D3 goes beyond simple efficiency. Recent research published in Frontiers in Immunology suggests that vitamin D2 and D3 have different roles in supporting immune function. Vitamin D3 appears to have a unique ability to strengthen your body's defenses against viruses and bacteria in ways that D2 does not.

According to researchers at the University of Surrey, vitamin D3 stimulates the type I interferon signaling system in your body, which serves as a first line of defense against bacterial and viral infections. This immune-boosting mechanism appears to be specific to D3.

"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," explained Professor Colin Smith from the University of Surrey.

Professor Colin Smith, University of Surrey

How to Choose the Right Vitamin D Supplement

• Check the Label: Look for vitamin D3 (cholecalciferol) rather than vitamin D2 (ergocalciferol) when selecting a supplement, based on current research showing D3's superior effectiveness.
• Consider Plant-Based Options: If you prefer plant-derived supplements, researchers emphasize the importance of ensuring plant-based vitamin D3 is accessible and available as an alternative to D2.
• Consult Your Doctor: Individual health needs vary, so discuss your specific vitamin D supplementation strategy with your healthcare provider to determine the right choice for your situation.
• Time Your Supplementation: Vitamin D supplementation is especially important during winter months (October through March in the UK) when sunlight exposure is limited and your body cannot produce vitamin D naturally.

The UK government recommends 10 micrograms of vitamin D daily, particularly during the winter months when sun exposure is insufficient for natural vitamin D production. Many people rely on supplements to meet this recommendation, making the choice between D2 and D3 increasingly important.

Researchers stress that further investigation into the different functionalities of vitamin D2 and D3 should be a priority in determining whether vitamin D3 should become the first-line choice for vitamin D supplementation. The findings suggest that public health recommendations and supplement formulations may need to shift to prioritize D3 over D2 for most individuals.

"Vitamin D deficiency represents a significant public health concern, especially during the winter months with significant deficiency across the UK population. 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," noted Professor Martin Warren, Chief Scientific Officer at the Quadram Institute.

Professor Martin Warren, Chief Scientific Officer, Quadram Institute

The discovery that vitamin D2 may actively reduce D3 levels represents a significant shift in how scientists think about vitamin D supplementation. Rather than assuming all vitamin D supplements work the same way, this research highlights the importance of understanding which form your body uses most effectively for both bone health and immune function.