There are 2 major types of oral vitamin D:
- vitamin D2 (ergocalciferol)
- vitamin D3 (cholecalciferol)
Human research studies
One of the first studies to compare the effects of vitamin D2 and vitamin D3 in humans was published in 1998 in the American Journal of Clinical Nutrition, the world's foremost, scientific nutrition journal. The title of this research study kinda gives away the outcome:
A 2004 in The Journal of Clinical Endocrinology & Metabolism supplemented volunteers with 50,000 international units of vitamin D2 or D3. These people were then followed for 28 days. Blood vitamin D levels coninuted to increased for the first 14 days in the D3 group. On the other hand, after an initial increase in blood vitamin D in the D2 group, vitamin D levels actually began to decrease! Therefore 14 days after a large dose of vitamin D2, blood vitamin D levels had actually not increased at all! The researcher wrote:
Vitamin D2 potency is less than one third that of vitamin D3. Physicians resorting to use of vitamin D2 should be aware of its markedly lower potency and shorter duration of action relative to vitamin D3.
A 2008 study in The Journal of Clinical Endocrinology & Metabolism reported that
'vitamin D3 is almost twice as potent as vitamin D2 in increasing blood levels of vitamin D'
A 2011 study in The Journal of Clinical Endocrinology & Metabolism compared vitamin D2 to vitamin D3 and concluded:
Vitamin D3 is approximately 87% more potent in raising and maintaining vitamin D blood concentrations and produces 2- to 3-fold greater storage of vitamin D than does the same amount of vitamin D2.
Given its greater potency and lower cost, D3 should be the preferred treatment option when correcting vitamin D deficiency.
A 2013 study published in The Journal of Clinical Endocrinology & Metabolism. Again, the title of this research study kinda gives away the outcome: 'Vitamin D3 seems more appropriate than D2 to sustain adequate levels of 25OHD'
In this study, the researchers compared the effects of the same dose of vitamin D2 to vitamin D3 to placebo. Total vitamin D levels increased more with vitamin D3 and the researchers concluded:
'Vitamin D3 increases the total vitamin D blood concentration more than vitamin D2'.
Another 2013 study, this time published in the British Journal of Nutrition again compared the effects of the same dose of vitamin D2 to vitamin D3 to placebo over 25 weeks. The researchers reported that: 'Overall, total blood vitamin D levels were 21 points lower in participants receiving vitamin D2 compared with those receiving D3' leading them to conclude:
'Daily supplementation of vitamin D3 was more effective than D2'
A 2015 human study published in European Journal of Clinical Nutrition examined the effect of vitamin D2 versus. vitamin D3 versus placebo. You can clearly see from this graph that vitamin D3 was most effective:
These researchers wrote:
'In the long term, D3 seems more appropriate for sustaining blood levels of vitamin D'.
A recent study in humans comparing vitamin D2 vs vitamin D3 supplementation in mostly D replete subjects indicated that total as well as free 25OHD increased more after vitamin D3 compared with vitamin D2 intake (20), without significant differences in changes in serum PTH in vitamin D3 vs vitamin D2-treated subjects.
Shieh A, Chun RF, Ma C, et al. Effects of high-dose vitamin D2 versus vitamin D3 on total and free 25-hydroxyvitamin D and markers of calcium balance. J Clin Endocrinol Metab. 2016;101:3070 – 3078.
A 2016 study in the The Journal of Clinical Endocrinology & Metabolism concluded that:
'vitamin D3 increased total and free 25D levels to a greater extent than D2'
A 2016 study in the British Journal of Nutrition examined the effect of bread fortified with either vitamin D2 or D3 and concuded:
'D2 is less potent in increasing total vitamin D blood concentrations than vitamin D3'
A 2004 review from 2 Canadian experts on vitamin D published in the American Journal of Clinical Nutrition and titled: The case against ergocalciferol (vitamin D2) as a vitamin supplement wrote:
'vitamin D3 has proven to be the more potent form of vitamin D in all primate species, including humans. The case that vitamin D2 should no longer be considered equivalent to vitamin D3 is based on differences in their efficacy at raising blood levels of vitamin D. Vitamin D2, or ergocalciferol, should not be regarded as a nutrient suitable for supplementation or fortification'.
A 2012 review of all the published studies (called a systematic review and meta-analysis) from multiple international vitamin D experts and led by Professor Susan Lanham-New was published in the American Journal of Clinical Nutrition. Interestingly, Professor Lanham-New conducted my university thesis viva interview in 2010!
Anyway, this 2012 article reviewed all the studies examining the effects of vitamin D2 vs. vitamin D3 and concluded:
Supplementation with vitamin D3 had a significant and positive effect in the raising of serum 25(OH)D concentrations compared with the effect of vitamin D2
This meta-analysis indicates that vitamin D3 is more effective at raising vitamin D levels than is vitamin D2, and thus vitamin D3 could potentially become the preferred choice for supplementation.
A 2016 scientific commentary written by vitamin D experts from Katholieke Universiteit, Leuven, Belgium and published in the academic journal 'Endocrinology' was titled: Is Vitamin D2 Really Bioequivalent to Vitamin D3?
This commentary wrote
'Most subjects who do not take vitamin D2 supplementation have nearly undetectable vitamin D2 concentrations in blood and thus this type of vitamin D may be less “natural” than generally claimed'