This Type of Vitamin D Is Twice as Effective as the One You’re Taking

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Vitamin D is key to maintaining bones, building muscle, repairing nerves, and supporting your immune system in the fight against cancer. But it’s easy to fall short on this vital nutrient if you live more than 37 degrees latitude north or south of the equator, since your body needs sunlight to manufacture D. (In the United States, imagine a line that runs from San Francisco through St. Louis, MO to Richmond, VA.) This is why doctors often recommend people take supplements to get the recommended minimum of 600 IU per day. The only hitch is that new research published in the American Journal of Clinical Nutrition suggests that one type of vitamin D—D3—is absorbed by the body much more readily than the commonly found D2.

A group of researchers from the University of Surrey in England recruited 335 healthy white and South Asian women between the ages of 20 and 64, all of whom were living in the United Kingdom. For three months in winter—to minimize the effects of sunlight—the researchers gave the women food that was fortified with vitamin D2, vitamin D3, or nothing. The women’s blood levels of vitamin D were tested at the start, midway through, and at the end of the study. The results were clear as day: Women who ate the food fortified with D3 experienced a significantly greater increase in blood levels of vitamin D.

“Our findings show that D3 is twice as effective as D2 in raising D levels in the body,” said study author, Laura Tripkovic, PhD, of the University of Surrey in England, in a press release. That means consuming D3, found in fish, eggs, most fortified milk, and D3-containing supplements, is twice as likely to raise your D levels than D2, which turns up in mushrooms, enriched bread, and D2-containing supplements.

It’s a thrilling discovery, says Dr. Tripkovic’s co-author Susan Lanham-New, PhD, of the University of Surrey as it could change how “the health and retail sector” view this important vitamin. Before long, our notion of the “best vitamin D” supplement may well transform into the “best vitamin D3 supplement.”

Wondering if you’re getting enough? Here are some of the signs you’re deficient in Vitamin D.