Vitamin D2 or D3 – Is That The Question?

Recently there has been a lot of talk that vitamin D3 is more effective than vitamin D2 in raising the level of the circulating form of total vitamin D in the blood. Even Dr. Mehmet Oz in this video suggests that you should prefer vitamin D3 to vitamin D2.

Is that really true?

Before we dig into the research, let us take a closer look at these two forms of vitamin D.

Vitamin D3, also known as cholecalciferol, is produced when ultraviolet rays (UVB) react with 7-dehydrocholesterol. This cholesterol molecule is naturally present in the skin of animals, including humans, and in milk.

Vitamin D2, also known as ergocalciferol, is derived from plant and fungal sources, such as mushrooms. Again, these plants contain a precursor molecule which converts to vitamin D2 when exposed to UVB rays.

Chemically, the difference between vitamin D2 and vitamin D3 molecule is very subtle.

According to a paper from Dr Michael Holick and coworkers, the notion of vitamin D2 not being as effective as vitamin D3 came about because of two recent reports which found that:

  1. vitamin D2 was less effective when given as 4000 IU/day for 2 weeks or as a single dose of 50,000 IU; and
  2. when a single dose of 50,000 IU was given to healthy adults, the serum level of vitamin D decreased more rapidly than the placebo group.

In the same paper, Dr Holick reports the results of his own research which divided the test subjects in 4 groups, each receiving one of the following for 11 weeks:

  1. a placebo
  2. 1000 IU/day of vitamin D2
  3. 1000 IU/day of vitamin D3
  4. 500 IU/day of vitamin D2 and 500 IU/day of vitmain D3

Sample size in each group ranged from 14 to 20.

The serum levels of the circulating form of vitamin D (25 hydroxy vitamin D) did not increase for the placebo group even though some of them took a multivitamin and drank milk.

The serum level of the vitamin D2 only group and the vitamin D3 only group increased to about the same level after 11 weeks. Same result was seen for the group that received both D2 and D3. In general, it was found that each 100 IU/day increased the serum level by 1 ng/mL over 11 weeks.

This result shows that both vitamin D2 and vitamin D3 are almost equally effective and that vitamin D2.

All subjects were vitamin D deficient at the start of the study; that is there average starting vitamin D level was about 17 – 20. After 11 weeks, the final average serum levels were less than 30 ng/mL. Dr Holick concludes that a higher level of vitamin D supplementation is needed to increase the serum level to the optimal range of 40 -60 ng/mL.

Although these results do show that both vitamin D2 and vitamin D3 are equally effective in raising serum levels, there are several limitations in this study which should prompt further investigation:

  1. Sample size in each group is small
  2. Standard deviation of both starting and final 25(OH)D levels are very high
  3. All starting levels were below 20 ng/mL. It would be interesting to see if vitamin D2 and D3 behave differently in subjects whose starting levels are high. There is a link between starting vitamin D level and increase in serum level per 1000 IU/day and it should be carefully evaluated.

The question still remains, but only from an academic point of view. Practically speaking, it doesn’t really matter whether you take vitamin D2 or vitamin D3. Always check your starting serum level and talk to your doctor before taking supplements.



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