Key points from article :
A new study led by Emily Brown at the University of Surrey, UK, and published as a meta-analysis of 11 clinical trials with 655 participants, has uncovered an unexpected effect of vitamin D supplementation. While both common forms of supplements—vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol)—were thought to be interchangeable, the analysis revealed that taking vitamin D2 can actually reduce levels of vitamin D3 in the body. This is significant because vitamin D3 is the form more efficiently used by the body and may play a unique role in immune defence.
Research suggests that vitamin D3, unlike D2, supports the type-I interferon system, which helps protect against infections. Brown and colleagues caution that although taking vitamin D2 will still raise total vitamin D levels, people may miss out on some of these additional immune benefits if relying solely on it. For this reason, D3 may be more beneficial for most individuals, though D2 remains a valuable option—particularly for vegans or those wishing to avoid animal products.
Experts note that personal circumstances matter. For example, older adults may benefit from D2 since their ability to convert D3 into its active form is less efficient. As Bernadette Moore of the University of Liverpool points out, for vegans or people who cannot access D3, taking D2 is still better than not supplementing at all. Meanwhile, plant-based D3 sources are emerging, including gene-edited tomatoes currently under study.
The findings highlight not only differences between vitamin D forms but also the importance of supplementation, especially in northern regions during winter, where deficiency can lead to fatigue, bone pain, and increased infection risk. As Brown’s colleague Susan Lanham-New emphasises, awareness of these subtle differences may help individuals make more informed choices to support their long-term health.
