New research has found significant differences between the two types of vitamin D, with vitamin D₂ having a questionable impact on human health. However, the study found that vitamin D₃ could balance people's immune systems and help strengthen defenses against viral infections such as COVID-19.

In a collaborative study by the Universities of Surrey and Brighton, researchers investigated the impact of vitamin D supplements—D₂ and D₃—taken daily over a 12-week period on the activity of genesin people's blood.

Contrary to widely held views, the research team discovered that both types of vitamin D did not have the same effect. They found evidence that vitamin D₃ had a modifying effect on the immune system that could fortify the body against viral and bacterial diseases.

Professor Colin Smith, lead-author of the study from the University of Surrey, who began this work while at the University of Brighton, said:

"We have shown that vitamin D₃ appears to stimulate the type I interferon signaling system in the body—a key part of the immune system that provides a first line of defense against bacteria and viruses. Thus, a healthy vitamin D₃ status may help prevent viruses and bacteria from gaining a foothold in the body.

"Our study suggests that it is important that people take a vitamin D₃ supplement, or suitably fortified foods, especially in the winter months."

Although some foods are fortified with vitamin D, like some breakfast cereals, yogurts, and bread,fewnaturally contain the vitamin. Vitamin D₃ is produced naturally in the skin from exposure to sunlight or artificial ultraviolet UVB light, while some plants and fungi produce vitamin D₂.

Many people have insufficient levels of vitamin D₃ because they live in locations where sunlight is limited in the winter, like the UK. The COVID-19 pandemic has also limited people's natural exposure to the sun due to people spendingmore time in their homes.

Professor Susan Lanham-New, co-author of the study and Head of the Department of Nutritional Sciences at the University of Surrey, said:

"While we found that vitamin D₂ and vitamin D₃ do not have the same effect on gene activity within humans, the lack of impact we found when looking at vitamin D₂ means that a larger study is urgently required to clarify the differences in the effects. However, these results show that vitamin D₃ should be the favored form for fortified foods and supplements."

The study has been published in Frontiers in Immunology.