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Prescription vitamin D2: Why not?

Posted on: December 21, 2012   by  John Cannell, MD


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:

  • First, Drisdol is not human vitamin D.
  • Secondly, the same habits that caused the vitamin D deficiency in the first place continue, and cause deficiency again, eventually, after treatment finishes.

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.

3 Responses to Prescription vitamin D2: Why not?

  1. Ron Carmichael

    Rather than suggesting that each person take 5,000iu of D3 per day, perhaps it might serve more people to adopt an approach based on weight – say, “5,000iu of D3 daily for each 100 pounds of weight”.

  2. Brant Cebulla

    Ron, obviously it’s a most accurate approach to recommend based on weight, absorption, blood levels, sun exposure habits etc…

    Counter to that, however, is that research shows time and time again, that people/patients often follow directions that are nice and simple and have fewest amount of steps.

    What we need is a controlled trial that compares approaches, and see what actually works best, so we can be evidence-based in how we recommend vitamin D. In such trial, you would communicate a simple “take 5,000 IU/day” in one group, and then communicate the “evaluate your habits/body, and take X amount/day based on YZ” to the other group. Then you can measure vitamin D levels before and after, and actually see what approach is “better”.

    For the time being, my guess is that a simple, “take 5,000 IU” results in more people taking vitamin D than a more personalized message. But who knows?

  3. [email protected]

    Veterinarians around thw world ceased giving vitamin D2 to mammals about 10 years ago. There have been >30 reports showing problems with giving vitamin D2 to humans during the past decade, yet the practice continues. Several studies found that the vitamin D blood levels actually DECREASED when taking vitamin D2.

    Be sure to have D3, not D2.

    See all of the reports and some graphs at http://is.gd/vitd3d2

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