"Vitamin D" refers to two biologically inactive precursors: D3 (cholecalciferol) and D2 (ergocalciferol). Both precursors are transformed in the liver and kidneys into 25-hydroxyvitamin D (25(OH)D, the non-active storage form, and the compound measured to assess vitamin D status). 25(OH)D is further converted to 1,25-dihydroxyvitamin D (1,25(OH)2D, the biologically active form) in a process that's tightly controlled by the body.
Although many researchers and experts agree that many people are vitamin D deficient and need supplementation, there remains a big question mark as to the most effective form.
Previous studies have reported that the D3 form is more potent than D2, with one study reporting that D3 was 87% more potent than D2. Recently, a systematic review and meta-analysis came to a similar conclusion--that that D3 was better than D2.
Now this new study further confirms these earlier findings. Researchers recruited 95 participants (aged 18 - 50) and divided them into 3 groups: placebo, 1000 IU/day of vitamin D2, and 1000 IU/day of D3. The intervention was carried out for 25 weeks starting at the end of summer.
What the results showed were surprising. They found that 1000 IU/day of vitamin D3 maintained 25(OH)D levels during winter months, whereas 25(OH)D levels decreased with 1000 IU/day of vitamin D2.
“These findings contribute to the accumulating evidence that vitamin D3 and vitamin D2 have different pharmacokinetic profiles for serum 25(OH)D,” wrote the researchers. “As a result, care should be taken to distinguish the form of vitamin D used for both clinical studies and therapeutic use, particularly given that the dose employed in the present study is commonly used in over-the-counter dietary supplements.
Source: Long-term vitamin D3 supplementation is more effective than vitamin D2 in maintaining serum 25-hydroxyvitamin D status over the winter months
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