The One Type of Vitamin D That Will Strengthen Your Immune System

Vitamin D is one of the most popular supplements in the United States, and for good reason too: it's known for its ability to contribute to bone strength and heart health, as well as lower your risk for developing an autoimmune disease. But there's a chance you're taking the supplement every day and not reaping all of its benefits. According to a study recently published in Frontiers in Immunology, D3 is more effective at elevating vitamin D levels in the bloodstream than D2. What's more, only D3 helps enable a critical immune system response to bacterial and viral infections.

To determine the key differences between both types of the supplement, the University of Surrey recruited 335 women between the ages of 20 and 64 who were based in the United Kingdom and randomly assigned them to a group. Some of the participants took 15 micrograms of vitamin D2 a day, while others took the same amount of D3. There was also a placebo group that took neither D2 or D3. The researchers examined the effects of vitamin D over a 12-week period during the winter months.

The result? Vitamin D3 was more effective at increasing vitamin D levels in the bloodstream than D2. They also found that the group who took D3 had a stronger immune system response to bacterial and viral infections, while D2 has the opposite effect. Additionally, it's believed by researchers that D2 may deplete D3, as the D2 supplement group had less D3 in their blood than the placebo group did. "We know that to take a vitamin D2 supplement actually displaces the normal, the native D3 from your body," Colin P. Smith, an author of the study and a professor of genomics at the University of Surrey in the U.K., told Inverse. "So by taking a vitamin D2 supplement, you could be making yourself vitamin D deficient, certainly in relation to some pathways in the body."

This isn't the first study that has examined the differences between D2 and D3. A study published last year in the National Library of Medicine, found that high D3 levels were associated with less severe depression symptoms in women, while D2 showed no such correlation.