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Many vegans and non-vegans have low vitamin D levels. Apart from synthesizing it with sunlight, it is possible to ingest it from the diet, but there are no natural, reliable vegan sources of vitamin D, as far as I know.

Vitamin D occurs in two vitamers, D₂ and D₃. D₂ occurs, e.g. in mushrooms and alfalfa sprouts. Vegan vitamin D₂ supplements are widely available.

Vitamin D₃ is typically produced from fish, or lanolin (wool fat). (Sheep, being vegan, take up vitamin D₃ by licking their own wool.) Although vegan D₃ supplements are sold, they're not as widely available as D₂ supplements.

It is sometimes claimed that vitamin D₂ is not as effective, or also not as bioavailable, as D₃. Is this true? Is vitamin D₂ less effective than vitamin D₃?

  • I think that "effective" may be a tough part of this question (perhaps too broad?) -- but "bioavailable" is more answerable biologically. – Erica Feb 5 '17 at 14:53
  • @Erica, yes, "effective" is hard to answer. For example, one could look at symptoms of vitamin D deficiency, and how good D₂ is at relieving them, compared to D₃. – Turion Feb 5 '17 at 14:59
  • Perhaps look for research simply on vitamin D levels, rather than deficiency symptoms (I've been dealing with moderate vitamin D deficiency for years and symptoms/improvements are subtle) -- ideally answers are going to be fairly quantifiable, rather than "I know I always feel better after eating mushrooms than after taking D3 supplements" – Erica Feb 5 '17 at 15:08
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+50

Vitamin D is often treated generically, sometimes even not specifying the index. According to this article, there are five Ds (D1, D2, D3, D4 & D5) and only D2 (ergocalciferol) and D3 (cholecalciferol) can be used by our bodies.

This article goes further and makes a difference between D2 and D3. D3 is clear winner (my emphasis):

The majority of studies that compare, and continue to compare, the effects of vitamin D2 and D3 all resonate with one statement: vitamin D3 is far superior for the human body. Research over the last ten years has produced an overwhelming amount of evidence that vitamin D3 is better absorbed and utilized than D2. Simply put, if you want the best form of vitamin D, choose vitamin D3.

Studies have consistently shown that, functionally, vitamin D3 is at least 300% more effective than D2. A review of over 50 vitamin D studies also shows that vitamin D3 offers a noticeable decrease in overall mortality, significantly surpassing D2 in reducing death rates from all causes. Vitamin D3 supplementation has also been shown to maintain serum vitamin D levels in the long run, especially in the winter months when sunlight is scarce.

Also, see references mentioned in the text (1, 2, 3, 4).

This article (a free account might be required to read it) goes into more medical details related to D3 vs D2 (its target audience is mostly health professionals):

Studies indicate that ergocalciferol (vitamin D2) is much less potent and has a shorter duration of action than cholecalciferol.

[...] ergocalciferol potency is less than 30% of that of cholecalciferol and that it has a markedly shorter duration of action.

Conclusion

[...] ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) are not bioequivalent and should not be considered interchangeable. Although few head-to-head trials exist, based on pharmacokinetic studies and limited clinical evidence, cholecalciferol is preferred over ergocalciferol.

Recommendation

Health professionals should encourage use of cholecalciferol (D3) over ergocalciferol (D2) in all patients without severe renal failure, either as a general supplement or as a treatment for vitamin D deficiency.



Answer to your question:

Yes, vitamin D₂ is less effective than vitamin D₃

  • Great answer, thanks for that! Following the information provided in your answer, hypothethically speaking, if one were to use a 2000 IU (or 50mcg) D2 supplement and eat some vitamin D fortified foods as well, this should be enough? I am asking because I currently have D2 supplements and would like to know whether to just ditch them or I can keep on using them and buy vegan D3 the next time. – Alexander Rossa Feb 18 '17 at 23:46
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    @AlexanderRossa - if you are worried about vitamin D levels, you can easily take a vitamin D blood test. It is one of the tests recommended for vegans. However, vitamin D deficiency can be caused by many other factors, as explained in this article: limited exposure to sunlight, dark skin, kidneys not working properly, absorbing problems etc. – Alexei Feb 19 '17 at 6:05
  • Is it possible to make up for the difference by simply taking more D2? – Alex Hall Feb 21 '17 at 11:03
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    @AlexHall - I cannot find an exact answer to your question, but taking D3 is clearly recommended (source]. This article says that in some cases, there is a small difference between efficient dozes and toxic ones for D2, so higher doses are risky. So, better use D3. – Alexei Feb 21 '17 at 11:50

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