Doctors in the USA often prescribe Drisdol (vitamin D2) for vitamin D deficiency, giving 50,000 IU every week or two for 8-12 weeks. Then, a few give it every month.
Too many forget about their patient’s vitamin D deficiency, thinking the Drisdol has cured it forever. There are two problems with this approach:
Vitamin D deficiency is not like strep throat; you don’t cure it and forget about it. It is something that must be continuously prevented via supplementation, or, better yet, UV exposure.
Now Dr Victoria Logan and colleagues of the University of Otago in New Zealand have added a third reason why Drisdol should not be prescribed. In a recent study, they have shown that not only is vitamin D2 less effective in raising 25(OH)D levels than vitamin D3, but that Drisdol actually lowers 25(OH)D3 levels. That is, when 25(OH)D2 is present in the blood, 25(OH)D3 levels go down.
Logan VF, Gray AR, Peddie MC, Harper MJ, Houghton LA. Long-term vitamin D3 supplementation is more effective than vitamin D2 in maintaining serum 25-hydroxyvitamin D status over the winter months. Br J Nutr. 2012 Jul 11:1-7.
They took 95 subjects, split them into three groups, and gave the first group 1,000 IU/day of vitamin D3, the next group 1,000 IU/day of vitamin D2 and the last group placebo, beginning at the end of their summer. The subjects began with total 25(OH)D levels of around 32 ng/ml, after the New Zealand summer.
Six months later, at the end of winter, total 25(OH)D levels had not changed in the D3 group (the 1,000 IU/day was just about enough to prevent the expected winter decline). As expected, the placebo group went from 32 ng/ml to 16 ng/ml. However, in the D2 group, the total 25(OH)D levels decreased significantly going from 32 ng/ml to about 24 ng/ml. That is, 1,000 IU/day of D2 resulted in lower total 25(OH)D levels.
Even more important, 25(OH)D3 levels dropped 21 ng/ml in the D2 group compared to dropping just 16 ng/ml in the placebo group. Vitamin D2 appears to trick the body into thinking that it has more vitamin D3 than it does. That is, the body will not start using 25(OH)D2 until it has used up most of the 25(OH)D3 the body has stored. Remember, D2 or Drisdol is metabolized into dozens of compounds that do not normally exist in the human body in such high quantities.
When will American doctors learn, the treatment for human vitamin D deficiency is human vitamin D. Humans need vitamin D3, about 5,000 IU/day, which will achieve natural levels in most people. My advice to doctors is to make sure you get your patients on daily D3, not weekly or monthly D2.