Like it or not, winter is here in Saskatchewan and vitamin D synthesis from sunlight is again negligible (even if we were brave enough to stand naked outside for an hour at noon). In past columns on Vitamin D I always recommended D3 over the frequently prescribed D2 form. Two studies published this year compared these two forms of vitamin D.
“Vitamin D supplementation for prevention of mortality in adults”, [www.ncbi.nlm.nih.gov/pubmed/21735411] published in July looked at 50 randomized trials with 94,000 participants over an average of 2 years. Of the 50 studies, 32 used D3 and 12 used D2. The remaining studies used two other forms of vitamin D – alfacalcidol and calcitriol. The authors found that D3 showed a significant decrease in mortality (deaths of participants from all causes) while the other forms had no significant effect.
Other findings in this meta-analysis were: that alfacalcidol and calcitriol increased the risk of hypercalcemia (excess blood calcium), and that D3 combined with calcium increased the risk of kidney stones. [Drinking sufficient water and taking vitamin K2 might alleviate the kidney stone risk.]
The other study “Vitamin D(3) is more potent than vitamin D(2) in humans” published in March, [www.ncbi.nlm.nih.gov/pubmed/21177785] compared the potencies of D2 and D3. This was a small trial involving 33 healthy adults given 50,000 units weekly of either D3 or D2 (because D is a fat soluble vitamin, it can be taken in weekly doses instead of daily). After 12 weeks vitamin D levels were measured in blood and subcutaneous fat. The study concluded that D3 was 87% more potent than D2 in raising blood levels, and produced 2 to 3 times the amount of stored vitamin D in fat. The study concluded: “Given its greater potency and lower cost, D3 should be the preferred treatment option when correcting vitamin D deficiency.”
This article is intended for educational purposes only; for medical advice consult your licensed health practitioner.
The common form of D3 is known as cholecalciferol. This is converted in the body (step one in the liver, step two in the kidneys) to the active form of D3, calcitriol, which is 1,25-dihydroxyvitamin D3. In some individuals whose conversion is impaired, supplementing with calcitriol is necessary.
ReplyDeleteVitamin D synthesized in the skin from cholesterol in the presence of UVB radiation undergoes several steps in becoming cholecalciferol.