New research suggests that vitamin D2 supplements, commonly available in the UK, can actually reduce levels of the more effective vitamin D3 in the body. This surprising finding raises questions about the widespread use of D2, especially as winter approaches when vitamin D levels naturally decline due to limited sunlight exposure.
The Problem with Vitamin D2
For years, vitamin D2 (ergocalciferol) has been a standard recommendation for supplementation, particularly for vegans and those avoiding animal products. However, a meta-analysis from the University of Surrey, published in Nutrition Reviews, reveals that taking D2 can lower the body’s concentration of vitamin D3 (cholecalciferol) – the form humans produce from sunlight and utilize more efficiently.
Researchers analyzed data from multiple randomized trials and found that participants taking D2 supplements often ended up with lower vitamin D3 levels than those who did not supplement at all. This isn’t just a minor difference; in some cases, D2 supplementation actively depleted D3 stores.
Why Vitamin D3 Matters More
“Vitamin D supplements are important, especially between October and March when our bodies cannot make vitamin D from sunlight,” explains Emily Brown, PhD, lead researcher on 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 difference isn’t just about blood levels. Separate research, including a study in Frontiers in Immunology, indicates that vitamin D3 plays a more critical role in supporting immune function. Specifically, D3 stimulates the type I interferon signalling system – a key component of the body’s first line of defence against viral and bacterial infections. Vitamin D2 does not appear to have the same effect.
“We have shown that vitamin D3, but not vitamin D2, appears to stimulate the type I interferon signalling system… a healthy vitamin D3 status may help prevent viruses and bacteria from gaining a foothold in the body,” says Professor Colin Smith of the University of Surrey.
Implications for Public Health
Vitamin D deficiency is already a significant public health issue, particularly in the UK during winter months when a large portion of the population falls below optimal levels. The findings suggest that current supplementation guidelines may need re-evaluation.
Professor Martin Warren of the Quadram Institute stresses the urgency: “Tackling this with the most effective form of vitamin D supplementation… is of the utmost importance to the health of the nation.”
While more research is needed to fully understand the long-term consequences of D2 supplementation, experts agree that prioritizing vitamin D3 – where feasible and appropriate – could be a more effective strategy for maintaining both adequate vitamin levels and robust immune function.
The key takeaway is simple: if you’re taking vitamin D supplements, consider whether D3 might be a better choice, especially if you’re concerned about supporting your immune system during the colder months.
