When you decide to spend money on a vitamin or supplement, you want to be sure it delivers. Which is why it can be a bit disheartening to walk down the vitamin aisle at the drugstore looking for a vitamin D supplement, only to see many different options that are all slightly different. Upon closer inspection, it seems to come down to vitamin D2 versus vitamin D3—so, which should you choose?

Meet the experts: Diane Han, M.P.H., R.D.N., L.D., a registered dietitian nutritionist based in San Francisco and the founder of Woking Balance Wellness; Lena Bakovic, M.S., R.D.N., C.N.S.C., a registered dietitian nutritionist at Live It Up.

Here, dietitians share the differences between vitamin D2 and vitamin D3, plus why you might want to take one over the other.

What is vitamin D?

Vitamin D is a fat-soluble vitamin that plays many essential roles in the body. “It is important for keeping our bones strong by aiding the absorption of both calcium and phosphorus. It also supports our immune system, keeps our muscles functioning properly, and has some anti-inflammatory properties,” says Lena Bakovic, M.S., R.D.N., C.N.S.C., a registered dietitian nutritionist at Live It Up. Yet as important as vitamin D is, it can be difficult to get enough of it.

“There is no superior way to get vitamin D. Getting vitamin D from a variety of sources is preferred,” says Diane Han, M.P.H., R.D.N., L.D., a registered dietitian nutritionist based in San Francisco and the founder of Woking Balance Wellness. Still, if you’re one of the 35% of adults in the United States who are deficient in vitamin D, a supplement may be a useful source.

There are four different ways to get vitamin D, according to the Mayo Clinic. The first is that the body can make vitamin D from direct sunlight on the skin. The second is to get it from foods in which it naturally occurs, and the third is to consume it via foods that have been fortified with vitamin D. The fourth, then, is to take a vitamin D supplement, which contains two subtypes: D2 and D3.

Vitamin D2 versus vitamin D3

“Vitamins D2 and D3 are used similarly in the body,” says Han. Both need to be converted in the body to calcitriol, which is the active form of vitamin D, or the form that your cells can actually use. Calcitriol is available as a prescription medication, per the National Library of Medicine; it’s used to treat low calcium and bone disease in patients with kidney or parathyroid dysfunction. But if you are looking to supplement with vitamin D, you’ll be choosing between one of these two inactive forms.

That said, there are a few key differences between D2 and D3, namely where they come from and how effective they are at improving vitamin D levels in the body (D3 seems to be slightly better in this department—more on that below).

Where does vitamin D2 come from?

“Vitamin D2, also called ergocalciferol, comes mainly from plant sources and fungi such as mushrooms. Interestingly, when mushrooms are exposed to sunlight or UV light, they produce D2,” says Bakovic. She adds that D2 is also added to some foods, the most common of which are dairy, soy, almond, and rice milk, yogurt, kefir, cheese, and orange juice, according to the Dietary Guidelines for Americans.

D2 is what is considered an inactive form of vitamin D, which means the body must transform it before being able to utilize it. “Once in your body, D2 is converted in the liver to a form called calcidiol, and then subsequently in the kidneys to calcitriol, which is the active form of D,” Bakovic explains.

What vitamin D2 does for your health

After vitamin D2 is converted to the active form of vitamin D, the body can then use it for the processes mentioned above, such as reinforcing bones and strengthening the immune system. According to the Mayo Clinic, vitamin D2 may also be used in treatment plans for hypoparathyroidism (underactive parathyroid glands), vitamin D-resistant rickets, and familial hypophosphatemia (low phosphorus in the blood), in addition to vitamin D deficiency.

Where does vitamin D3 come from?

“Vitamin D3, or cholecalciferol, is another inactive form of vitamin D. Its sources include skin exposure to sunlight and animal-based foods such as salmon, sardines, egg yolks, and liver,” says Han. Similar to D2, D3 needs to go through a conversion process before the body is able to use it.

What vitamin D3 does for your health

“There aren’t any specific processes that require D3 exclusively,” says Bakovic. “However, because it’s more bioavailable [meaning it enters the circulation and is able to impact the body], it is usually more effective in the prevention and/or correction of a Vitamin D deficiency.”

This is the key way in which vitamin D3 differs from D2. A 2024 review published in Advances in Nutrition analyzed 20 studies that compared the efficacy of vitamin D2 versus vitamin D3 for raising the levels of vitamin D in the body and found that vitamin D3 was better at raising total vitamin D concentration in the blood. However, the researchers also found that when they looked at the concentration of hydroxylated (or active) vitamin D, the difference between D2 and D3 was negligible, especially in people who were taking it daily. So while D3 supplements do appear to be more bioavailable, both forms of vitamin D can be effective for combating vitamin D deficiency.

The bottom line

While vitamin D3 has been shown to be more effective at raising vitamin D levels when they are low, both D3 and D2 are easily converted in the body into the active, usable form we need to support key processes and optimize health. Still, the best thing to do before deciding which one to take is to talk to your doctor. They can help you determine if you can safely take vitamin D (it may interact with some medications and shouldn’t be taken if you have certain other medical problems, per the Mayo Clinic) and how much to take to get the benefits you are looking for.

Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing. Also, be careful about giving supplements to a child, unless recommended by their healthcare provider.

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