By Hendra Lukman 
New research emerging from a collaborative effort between the University of Surrey, the John Innes Centre, and Quadram Institute Bioscience has raised significant questions about the efficacy of vitamin D2 supplementation, suggesting it may inadvertently lower the body’s levels of the more potent and naturally produced vitamin D3. This finding holds particular relevance for individuals in the UK and globally who rely on supplements to meet daily vitamin D recommendations, especially during periods of limited sun exposure. The study, published in the esteemed journal Nutrition Reviews, analysed data from a comprehensive meta-analysis of randomized controlled trials, uncovering a previously unrecognised interaction where vitamin D2 intake appears to decrease circulating concentrations of vitamin D3.
Understanding the Forms of Vitamin D
Vitamin D is a crucial fat-soluble vitamin essential for numerous bodily functions, including bone health, immune system regulation, and cellular growth. The human body can produce vitamin D when skin is exposed to ultraviolet B (UVB) radiation from sunlight. However, this process is significantly limited in regions with less intense sunlight, such as the UK, particularly during the autumn and winter months (typically October to March). To address this deficiency, many individuals turn to dietary supplements, which are widely available in two primary forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Vitamin D3 is the form naturally synthesized by the skin upon sun exposure and is also found in animal-based foods like fatty fish and egg yolks. It is widely considered the more efficient form for raising and maintaining blood levels of vitamin D. Vitamin D2, on the other hand, is primarily derived from plant sources, such as mushrooms exposed to UV light, and is commonly used in fortified foods and some vitamin D supplements. Historically, both forms have been used interchangeably to combat vitamin D deficiency. However, the latest research from the University of Surrey and its partners indicates a potential divergence in their physiological impact.
Unveiling the Unexpected Interaction
The meta-analysis, a rigorous scientific approach that combines the results of multiple independent studies, examined existing randomized controlled trials to assess the impact of vitamin D2 supplementation on vitamin D3 levels. The findings were consistent and striking: in a significant number of the analysed studies, individuals who took vitamin D2 supplements exhibited lower concentrations of vitamin D3 in their blood compared to control groups who did not receive vitamin D2. In some instances, the vitamin D3 levels in the vitamin D2 supplementation groups dropped below those observed in the control participants, suggesting a direct antagonistic effect.
Dr. Emily Brown, PhD Research Fellow and Lead Researcher from the University of Surrey’s Nutrition, Exercise, Chronobiology & Sleep Discipline, underscored the significance of these findings. "Vitamin D supplements are important, especially between October and March, when our bodies cannot make vitamin D from sunlight in the UK," she stated. "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 to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2."
This discovery challenges the long-held assumption that both forms of vitamin D are equally effective in raising overall vitamin D status. The implication is that while vitamin D2 might contribute to the total vitamin D pool, it could be at the expense of the body’s more readily utilised and potentially more functionally important vitamin D3.
A Deeper Dive into Immune Function
The implications of this research extend beyond mere vitamin D levels, potentially impacting the body’s ability to defend against infections. This new study builds upon previous work, including research published in Frontiers in Immunology led by Professor Colin Smith from the University of Surrey. That earlier study suggested that vitamin D2 and D3 do not share identical roles in supporting immune function. Specifically, vitamin D3 was found to have a modulatory effect on the immune system that could enhance the body’s resilience against viral and bacterial pathogens.
Professor Colin Smith elaborated on these findings: "We have shown that vitamin D3, but not vitamin D2, appears to stimulate the type I interferon signalling system in the body – a key part of the immune system that provides a first line of defence against bacteria and viruses. Thus, a healthy vitamin D3 status may help prevent viruses and bacteria from gaining a foothold in the body." The type I interferon system is a critical component of the innate immune response, playing a crucial role in antiviral defence by inhibiting viral replication and activating other immune cells. The observation that vitamin D2 does not elicit this same response, coupled with the new findings of its potential to reduce vitamin D3 levels, raises concerns about its adequacy in bolstering immune defences.
The Importance of Plant-Based Vitamin D3 Accessibility
The research also highlights the ongoing need for accessible sources of vitamin D3, particularly plant-based options, to cater to diverse dietary needs. Professor Cathie Martin, Group Leader at the John Innes Centre, commented on this aspect: "This meta-analysis highlights the importance of ensuring plant-based vitamin D3 is accessible in the UK." As a growing number of individuals adopt vegetarian and vegan diets, the demand for plant-derived nutrients, including vitamin D3, is increasing. Historically, vitamin D3 has been predominantly sourced from animal products, leading to a reliance on vitamin D2 for plant-based diets. However, if vitamin D2 proves to be less effective and potentially detrimental to vitamin D3 levels, the development and availability of effective plant-based vitamin D3 sources become paramount.
Public Health Implications and Future Directions
Vitamin D deficiency remains a significant public health concern globally, with substantial segments of the population experiencing suboptimal levels, particularly during winter. Professor Martin Warren, Chief Scientific Officer at the Quadram Institute, emphasized this point: "Vitamin D deficiency represents a significant public health concern, especially during the winter months with significant deficiency across the UK population." He further stated, "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."
The findings necessitate a re-evaluation of current public health recommendations and supplement guidelines. While the UK government advises 10 micrograms (approximately 400 IU) of vitamin D daily, especially during winter, the specific form of vitamin D recommended for supplementation has not been definitively clarified in light of this new evidence. The research team suggests that further investigation into the distinct functional roles of vitamin D2 and D3 should be a priority. This deeper understanding will be instrumental in guiding decisions on whether vitamin D3 should be promoted as the first-line choice for vitamin D supplementation, always considering individual requirements and health profiles.
Potential Timeline of Understanding Vitamin D
The understanding of vitamin D and its different forms has evolved over decades:
- Early 20th Century: Rickets, a bone-deforming disease, was prevalent in children in industrialized nations. Researchers identified that sunlight and certain foods could prevent and cure it. This led to the discovery of vitamin D.
- 1920s-1930s: Vitamin D was identified and isolated. The distinction between vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) emerged, with D3 being identified as the form produced by skin and found in animal sources.
- Mid-to-Late 20th Century: Vitamin D supplementation became a common public health strategy to prevent rickets. Both D2 and D3 were widely used, often with less emphasis on their differing efficacies.
- Early 21st Century: Increased research began to explore the nuanced roles of vitamin D in various bodily functions beyond bone health, including immune regulation. Studies started to suggest potential differences in how D2 and D3 are metabolized and utilized.
- 2010s-Present: A growing body of evidence has increasingly favoured vitamin D3 for its superior ability to raise and maintain blood vitamin D levels. This latest meta-analysis from the University of Surrey and its collaborators directly challenges the efficacy of vitamin D2, suggesting it may actively reduce the levels of the more beneficial D3.
Supporting Data and Further Research Needs
While the current study is a meta-analysis, drawing conclusions from existing randomized controlled trials, it signals a strong direction for future research. Key areas for further investigation include:
- Direct Comparison Studies: Rigorous, long-term studies directly comparing the effects of vitamin D2 and vitamin D3 supplementation on both vitamin D status and specific health outcomes, such as immune markers and bone density, in diverse populations.
- Mechanistic Studies: Research to fully elucidate the biochemical pathways by which vitamin D2 might interfere with vitamin D3 metabolism or absorption. Understanding these mechanisms is crucial for confirming the observed effects and identifying potential interventions.
- Population-Specific Needs: Investigations into whether certain demographic groups or individuals with specific health conditions respond differently to vitamin D2 versus D3.
- Fortification Strategies: A review and potential revision of fortification practices for foods and beverages to ensure the most effective form of vitamin D is utilized to combat deficiency.
The consistent findings across multiple studies within the meta-analysis provide robust evidence to warrant caution regarding vitamin D2 supplementation. The implication that it may not only be less effective but could actively hinder the body’s ability to maintain sufficient levels of vitamin D3 is a significant development in our understanding of nutritional science. As the public health landscape continues to grapple with widespread vitamin D deficiency, this research offers critical insights that could inform future recommendations and lead to more effective strategies for ensuring optimal vitamin D status for populations worldwide. The call for accessible plant-based vitamin D3 further underscores the need for innovation in nutritional science to meet the evolving dietary needs of a global population.
