Recently on the Toronto Vegetarian Podcast there has been a lot of discussion about Vitamin D. One of our podcast listeners (Hi Michelle!) who is in her final year of med school at Harvard (Congrats, Michelle!) had the below information to add to the discussion. There were lots of good points made in her email and I'd thought I'd post it here for anyone looking for more info.
Thanks for listening to the podcast Michelle and for providing us with the below info.
What are the types of vitamin D supplements?
-- Vitamin D2 is ergocalciferol (yes, as you mentioned, the vegan one made from a component of fungi) - the brand name in the U.S. is Drisdol, brand names in Canada are both Drisdol® and Ostoforte®.
-- Vitamin D3 is cholecalciferol (the one made from lanolin, a sheep’s wool derivative)– Canadian brand name is D-Vi-Sol®; U.S. has many brand names.
-- Calcidiol (25-hydroxyvitamin D) is used mainly for patients with liver disease.
-- Calcitriol (1,25-cholecalciferol) (the numbers just indicate the places on the vitamin D molecule that have the hydroxylations) is used mainly for patient with kidney failure.
Why can I only find D3 (and not D2) in stores?
The only form of vitamin D commonly found over-the-counter in the US (and, from your podcast, it sounds like Canada, as well) is D3. In the US, a prescription is required for D2. A personal comment – because D2 is usually a prescribed supplement, there is a chance that the “D2” you’re buying over-the-counter is actually mislabeled (for either innocent reasons, or because someone knows they can make a buck) D3 or something other than vitamin D entirely. Before giving up on D2 and moving to a non-vegan D3, you may want to ask your doctor for a prescription for D2. Just a thought.
What are the differences between the four types of vitamin D above?
Let’s start with how naturally-occurring “vitamin D” works in the body. A precursor molecule is converted to D3 in the skin by the sun, hence taking D3 bypasses the need for the sun (D2 is pretty similar to D3 molecularly). To become active, vitamin D3 must be hydroxylated (a chemical reaction/change) in two places on the molecule. The liver takes care of the first one, and the kidney takes care of the next. People who have normal liver and kidneys can take either vitamin D2 or D3 supplements. When significant kidney or liver problems are the cause of vitamin D deficiency, those people need a different supplement that is already hydroxylated (Calcidiol for liver problems and Calcitriol for kidney failure).
Is D3 “more potent” or “more effective” than D2? (i.e. do I need to take a non-vegan D3 supplement to make sure that I’m healthy?)
The main thing to remember is that different people absorb vitamin D at different rates. If you don’t have problems you’re your digestive tract and can generally absorb things fine, you still may need a bit more or less vitamin D supplement to get to healthy blood levels. This can be achieved by adjusting doses of either D2 or D3. Basically, if a dose isn’t working for you, take more. If you have normally-functioning kidneys, liver and other organs (it seems like you podcasters do) then you should be able to deal just fine with either D2 or D3 just fine after they’re absorbed. The evidence about whether D3 is the same or different than D2 in humans comes from 4 main studies. Three of the studies showed that D3 was “more potent” than D2 – however all three studies used very high doses of both (i.e. much different than you would be taking at home). All three also showed that D2 increased blood vitamin D levels, even if not as much as D3 at the same very high doses. The study that had the best design (according to rigorous academic and research standards) and used a 1000 IU dose (i.e. a normal daily maintenance dose) of both for comparison showed no difference between D2 and D3.
How much vitamin D should I – someone who is vitamin D deficient, but otherwise “normal” – be taking?
With all of the new discoveries about the importance of vitamin D for preventing cancer, keeping the immune system working, the cardiovascular system healthy, et cetera, the recommended daily doses are currently being revised upward. The previous recommendation was 400 IU per day, but this is only to prevent severe deficiency diseases like rickets or osteomalacia. It is thought that much more is needed for cancer prevention and immune system (etc.) function. What we are currently learning at Harvard Medical School is that 1000 IU is likely a better baseline daily dose, and that either taking a larger daily dose (like 2,000 IU per day) or even getting very large dose injections of vitamin D weekly are needed to bring vitamin D blood tests into the normal range. The “normal range” is also being revised upward. This means that the new “low-normal” will no longer be 75 nmol/L, but will be change to a larger number (sorry, yes this means that you’re even more deficient that you thought!).
All this to say – get your vitamin D and stay a healthy, happy vegan!
I hope this is helpful. Thanks again for the great podcast – I am looking forward to listening to some more of them!
All the best,