A 2015 single-blind study found that vitamin D3 supplements may be better than vitamin D2 supplements at sustaining vitamin D blood levels. D2, also called ergocalciferol, and D3, also called cholecalciferol, are different forms of vitamin D that have similar, though not identical, actions in the body. Published in the European Journal of Clinical Nutrition, the study divided 33 healthy people into three groups: one group received a placebo, the second received D2, and the third received D3. The two vitamin D groups started off with a very large, single dose of 100,000 IU, followed by 4,800 IU per day starting at day seven for another two weeks. After tracking the participants’ blood levels for 77 days, the researchers concluded that:
At least at first, D2 and D3 were about as equally effective at raising vitamin D levels.
However, D3 was better at sustaining vitamin D blood levels: at day 77, those receiving D3 had higher levels of vitamin D than either the D2 group or the placebo group.
These findings are consistent with other research which has shown that D3 is a more effective form of vitamin D. While more research is needed to confirm these results, in the meantime, consumers might still want to choose D3 supplements to be sure they get the most out of their vitamin D.
Source: European Journal of Clinical Nutrition