The supplement aisle can be chaotic — an endless wall of brands and formulations to supposedly support every aspect of your mental and physical health (plus some body parts you didn’t know could glitch out!) Luckily your doc just said to pick up some plain old vitamin D — that should be a quick dash to the register, right?
Yeah, no. Not only are there tablets and gel caps and gummies in different dosages and paired with minerals, like calcium, but then there’s the choice between vitamin D2 and vitamin D3.
If your doctor didn’t specify, which one should you get? You want to follow their recommendation, without wasting money on pills you don’t need or ones that won’t work as well as they should.
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Vitamin D2 vs. vitamin D3
Let’s start here: What is the difference between D2 and D3? “People get confused about D2 and D3 because they have heard about multiple B vitamins, like B9 and B12,” says Carol Haggans, MS, RD, a spokesperson for the NIH Office of Dietary Supplements. “Those different B vitamins are actually distinctly different nutrients.” Vitamin B9, for example, is folate, which is recommended for pregnant women to prevent birth defects; B12 is cobalamin, which works to keep your blood and nerve cells healthy, and helps make DNA.
Vitamin D2 and D3, however, are not different nutrients. “They are essentially the same compound,” says Haggans, with only a slight chemical difference in their side chain structure. Still, while both are vitamin D and can help you raise your blood levels, they are not exactly the same.
- Is called cholecalciferol
- D3 is what your body produces when your skin is exposed to sunlight
- It can also be found in fish (fatty ones such as trout, salmon, tuna and mackerel) and fish liver oils, as well as other animal products.
- It is the version most often used in fortified foods, such as milk, cereal and OJ, says Haggans.
- D3 supplements are made from an irradiated compound in lanolin, which comes from sheep wool (though there is an animal-free version made from lichen)
- Is called ergocalciferol
- You can only get it by eating fortified food or dietary supplements (not from sunlight)
- D2 supplements are derived from plant products, specifically a compound in yeast that has been zapped with UV light
- It can sometimes be found in mushrooms, particularly those that are treated with UV-light to up their D2 content
- Plant-based foods are often fortified with D2, though many cereals and orange juices have D3
Is it better to take vitamin D3 supplements instead of D2?
To be clear: Both forms of vitamin D help you absorb calcium, which is key for the health of your bones. Your muscles and nerves need it to function, and it helps to support your immune system. But “vitamin D3 is more bioavailable (a.k.a has a stronger ability to be absorbed and used in the body), which is why people tend to prefer vitamin D3,” says JoAnn Manson, M.D., MPH, DrPH, a Professor of Medicine at Harvard Medical School and chief of the Division of Preventive Medicine at Brigham and Women’s Hospital in Boston.
When researchers had folks take the vitamin D2 and D3 at the levels most people take, “there was a greater rise in the blood levels of vitamin D3,” she says, which is how they know if you have sufficient amounts to keep you well. “There is evidence that D3 increases serum levels better, and that vitamin D levels maintain those higher levels longer than D2,” agrees Haggans.
That said, both vitamin D3 and D2 are well absorbed in the gut, and both work well to raise blood levels of vitamin D. “It’s not a tremendous difference — it’s not like [D3 is] twice as bioavailable as D2,” says Dr. Manson, who adds that it’s hard to precisely measure the effects of each supplement in the blood because people get vitamin D in other ways, such as through sun exposure and food.
One thing to keep in mind: Vitamin D2 supplements are derived from plant materials, so if you follow a vegan diet or avoid animal products for other reasons, D2 is a better choice for you. D2 is sometimes added to plant-based products. “Most fortified products will indicate what form of vitamin D they used,” says Haggans. If you don’t see it indicated on the label of food or supplements, contact the manufacturer, who should be able to tell you.
Why do doctors prescribe vitamin D2 instead of D3?
They don’t always, and for most people, D3 is a better option because it is more effective in raising your blood levels when you supplement daily, says Dr. Manson.
But if someone needs a bolus dose (that is, a very high dose given over a short period of time to correct a deficiency) doctors sometimes use D2, says Dr. Manson, as it has historically been available in very high doses.
Keep in mind: You should never take large doses of either form of vitamin D unless your doctor specifically prescribes it. “You don’t want to go on anything above the upper limit for any length of time,” says Haggans. (For healthy people between 12 months and 70 years of age the recommended daily dose is 600 IU, but Dr. Manson’s research indicates that it is safe to take 1000-2000 IU a day “as a type of insurance” to make sure you’re getting enough, she says.) Under no circumstances, says Dr. Manson, should you exceed 4000 IU of vitamin D in a day, including all sources. Very high levels can cause vomiting, muscle issues, pain and confusion, among other things, according to the NIH.
If your doctor recommends a supplement, it’s wise to ask how much to take and when your blood will be next checked to make sure your levels have been raised sufficiently, says Haggans. “You might only need to for a period of time to boost levels up,” she adds.
Bottom line: It doesn’t much matter which you take, unless you want to avoid animal products, says Dr. Manson, in which case D2 is a better choice. D3 is better at raising blood levels of vitamin D, but D2 also works well. The main thing, says Dr. Manson, is to take whichever you choose along with a bit of food that contains fat. That’s because vitamin D is absorbed better with fat, and explains why one formulation you’ll see in the vitamin aisle are gel caps containing oil. As with all supplements, choose your brands carefully. Dietary supplements are not approved by the FDA prior to going to market, so ask your doctor for a reputable brand, or look for ones that are labeled third-party tested for purity, potency and safety and can confirm that what is on the label is actually what is in the bottle. NSF or USP logos will indicate that the testing has been done.
Stephanie (she/her) is the deputy director of the Hearst Health Newsroom, where she writes, edits and otherwise creates health content for Good Housekeeping, Prevention and other Hearst titles. She has covered women’s physical and emotional health, nutrition, sexuality and the multitudes of topics they contain for national publications for decades, and she is also a bestselling author, a mom of twins, a dog mom and an intuitive eater in progress.
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Stefani (she/her) is a registered dietitian, a NASM-certified personal trainer and the director of the Good Housekeeping Institute Nutrition Lab, where she handles all nutrition-related content, testing and evaluation. She holds a bachelor’s degree in nutritional sciences from Pennsylvania State University and a master’s degree in clinical nutrition from NYU. She is also Good Housekeeping’s on-staff fitness and exercise expert. Stefani is dedicated to providing readers with evidence-based content to encourage informed food choices and healthy living. She is an avid CrossFitter and a passionate home cook who loves spending time with her big fit Greek family.