Longevity
Vitamin D2 vs. D3: What's the Difference?
By Life and Health Today Staff, . Life and Health Today.
Vitamin D supplements come in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Both are converted by the liver into the same circulating form the body measures, 25-hydroxyvitamin D, and both can correct a deficiency. They are not identical, though, and the difference matters when choosing a supplement.
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Where Each Form Comes From
Vitamin D2 comes from plants and fungi. It is made when yeast or mushrooms are exposed to ultraviolet light, and it is the form in some fortified foods and in the high-dose prescription capsules doctors often use to treat deficiency.
Vitamin D3 is the form human skin makes when exposed to the sun's UVB rays. In food it comes from animal sources such as fatty fish, egg yolks and liver, and it is the form in most over-the-counter supplements. Most D3 supplements are made from lanolin, the oil in sheep's wool; vegan D3 made from lichen is also available.
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Which Works Better
Both forms raise vitamin D levels, but most studies have found D3 more effective at raising and keeping up blood levels of 25-hydroxyvitamin D. A meta-analysis published in the American Journal of Clinical Nutrition in 2012 found D3 raised levels more than D2, mainly when given in large, infrequent doses, and a later randomized trial by the same research group, published in the same journal in 2017, found D3 more effective in winter, when sun exposure is low.
The difference appears to come from how the body processes each form, with D3 staying in circulation longer. For most people buying a supplement on their own, that is why D3 is the usual choice. D2 remains useful, particularly for people who avoid animal products and in prescription doses a doctor is monitoring.
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How Much Vitamin D Adults Need
According to the National Institutes of Health Office of Dietary Supplements, the recommended daily amount is 600 IU (15 micrograms) for people aged 1 to 70 and 800 IU (20 micrograms) for adults over 70. The upper limit for adults is 4,000 IU (100 micrograms) a day, unless a doctor prescribes more to treat a deficiency.
Blood levels of 25-hydroxyvitamin D below 12 ng/mL are generally considered deficient, while 20 ng/mL is generally considered adequate for bone health for most people, according to the same NIH guidance. Very high levels, above about 50 ng/mL, have been linked to possible harm.
In 2024 the Endocrine Society advised against routine vitamin D testing in the general population, and suggested supplementation without testing for some groups, including children and teens, adults 75 and older, pregnant people and adults with high-risk prediabetes.
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Getting the Most From a Supplement
Vitamin D is fat-soluble, so taking it with a meal that contains some fat can help absorption.
Check the label for the form (D2 or D3) and the dose in IU or micrograms, since 1 microgram equals 40 IU.
More is not better. Vitamin D builds up in the body, and taking well above the upper limit for long periods can raise calcium levels to a harmful degree.
People with kidney or liver disease, those taking medications that affect vitamin D or calcium, and anyone considering high doses should talk with a doctor first. A blood test is the only way to know a person's actual level.
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The Bottom Line
D2 and D3 both work, but D3 does a better job of raising and holding vitamin D levels, which is why it dominates the supplement shelf. Most adults need 600 to 800 IU a day from food and supplements, and doses above the 4,000 IU upper limit belong under a doctor's supervision.
Life & Health Today provides information for educational purposes only, not medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.