Longevity
Vitamin D2 supplements found to lower the body's own D3 levels
By Life and Health Today Staff, . Life and Health Today.
A meta-analysis published in the journal Nutrition Reviews in 2025 found that people taking vitamin D2 supplements had meaningfully lower blood levels of vitamin D3 than people who did not take D2. The research was led by Emily Brown, a PhD Research Fellow at the University of Surrey's Nutrition, Exercise, Chronobiology and Sleep Discipline, working with colleagues at the John Innes Centre and Quadram Institute Bioscience.
Vitamin D comes in two main supplemental forms. D2, also called ergocalciferol, is typically made from fungi or yeast exposed to ultraviolet light, which makes it suitable for vegans. D3, or cholecalciferol, is the same form the body produces when skin is exposed to sunlight, and it has traditionally been derived from lanolin in sheep's wool, though plant-based versions from lichen are now available. Both forms raise total vitamin D status, but guidance from the United States National Institutes of Health states that D3 tends to produce a larger increase and sustain it for longer.
The 2025 analysis drew on 20 studies, with 11 providing data suitable for the main statistical pooling. Compared with people who received no D2, those who took it had lower concentrations of 25-hydroxyvitamin D3, the D3-derived compound that doctors measure in blood tests to assess vitamin D status. Depending on how the results were analysed, the average reduction ran from roughly 9 to 18 nanomoles per litre, according to ScienceDaily Nutrition's account of the paper.
Brown told ScienceDaily Nutrition that supplements matter most between October and March, when bodies in the UK cannot make vitamin D from sunlight. The surprise was what the D2 form did alongside that: "vitamin D2 supplements can actually decrease levels of vitamin D3 in the body", an effect she described as previously unknown.
The researchers proposed one possible mechanism: when vitamin D metabolites, the compounds the body produces as it processes vitamin D, rise in the blood, the body may speed up their breakdown to keep levels in check. Raising D2 metabolites could therefore accelerate the disposal of existing D3 metabolites. Earlier experiments have also suggested the relationship runs in both directions, with D3 supplementation sometimes reducing D2-derived compounds.
The finding does not mean D2 is inert or harmful. A separate 2026 systematic review and meta-analysis of 26 randomised trials, also reported by ScienceDaily Nutrition, found that D2 supplementation significantly reduced parathyroid hormone levels, a hormone that regulates calcium in the blood, and produced a small increase in blood calcium itself. D2 continues to have measurable biological effects even as it appears to suppress circulating D3.
A separate line of research, published in Frontiers in Immunology and led by Professor Colin Smith of the University of Surrey, examined gene activity in the blood after supplementation with each form. The study found that D3, but not D2, appeared to stimulate type I interferon signalling, a set of immune proteins that help alert cells to developing infections. Smith was quoted by ScienceDaily Nutrition as saying that "a healthy vitamin D3 status may help prevent viruses and bacteria from gaining a foothold in the body." Changes in gene activity are not the same as clinical protection, however, and larger trials would be needed to establish whether the immune difference translates into fewer actual infections.
Professor Cathie Martin, Group Leader at the John Innes Centre, said the analysis "highlights the importance of ensuring plant-based vitamin D3 is accessible in the UK," pointing to lichen-derived D3 as a practical option for people who avoid animal products.
What the accumulated evidence does not yet settle is whether the reduction in D3 caused by D2 supplementation produces any difference in health outcomes that a person would notice or that a clinical trial could measure. The researchers called for additional studies on how the two forms are metabolised, whether their immune effects diverge in ways that matter, and whether D3 should become the default recommendation when no individual reason exists to use D2.
Anyone weighing which form to take should raise the question with a clinician who knows their full health picture, including diet, sun exposure and any existing deficiency.
Source: https://www.sciencedaily.com/releases/2026/10/261007232940.htm
Life & Health Today provides information for educational purposes only, not medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.