A new meta-analysis published in Nutrition Reviews by researchers from the University of Surrey examined 11 randomised controlled trials involving healthy participants. The team found that people who took vitamin D₂ supplements experienced a greater decline in circulating vitamin D₃ levels than those who took no supplements.
“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 study author. “This study suggests that, subject to personal considerations, vitamin D₃ supplements may be more beneficial for most individuals over vitamin D₂.”
Brown explained that vitamin D₃ may not only raise total vitamin D concentrations more effectively but could also better support immune function:
“[These results suggest that] vitamin D₃ supplementation may be the preferable supplement over vitamin D₂ … due to increased efficacy at raising total [serum vitamin D] concentrations and possible additional functionality vitamin D₃ has in modifying the immune system.”
Experts say this research adds weight to the idea that supplements are not interchangeable.
“Vitamin D₃ should be prioritised for supplementation, as D₂ can lower circulating D₃ levels,” said Lina Begdache, PhD, RDN. Endocrinologist Dr Malek Cheikh agreed, noting that “it may be safer to depend on D₃ rather than on D₂ to boost vitamin D levels.”
Vitamin D₃ appears to deliver stronger, more consistent results for most people. However, those on plant-based diets may still use D₂, ideally under medical supervision.
The findings reinforce an approach that values informed, individual choice, helping people take responsibility for their health through evidence-based, accessible options rather than one-size-fits-all advice.