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Vitamin D: What’s the difference between D2 vs. D3?

By: Jennifer Fleming PhD, MS, RD, LDN

If you are concerned you are not getting adequate Vitamin D through sunlight and food intake, you’ll likely need to supplement. There are two widely available forms of Vitamin D that can be found over the counter: Vitamin D2 (“ergocalciferol” or pre-vitamin D) and Vitamin D3 (“cholecalciferol”). Both are naturally occurring forms that are produced in the presence of the sun’s UVB rays. However, D2 is produced in plants and fungi, and D3 is produced in animals––including humans.

In general, both Vitamins D2 and D3 function as prohormones, with the only difference between the two being the structure of their side chains. Both D2 and D3 have to pass through your liver and kidneys to be converted to the active form of Vitamin D.

But is one better than the other?

Vitamin D2 has been the mainstay of therapy for over 80 years and is the only form in prescription preparations. Yet, there is ongoing debate that Vitamin D3 is better than Vitamin D2 at increasing blood levels of the vitamin.

To break it down, both Vitamins D2 and D3 undertake identical metabolic processes, resulting in the same active form of Vitamin D. However, studies show that, in comparison, there may be a difference in their respective abilities to raise serum concentrations.

A meta-analysis of randomized controlled trials (considered the best type of trials), compared the effects of Vitamin D2 and D3 supplements on blood levels. Guess what they found: D3 supplements tended to raise blood concentrations of the vitamin more and sustained those levels longer than D2.

With other bodies of research to take into consideration, it appears that at nutritional doses, Vitamins D2 and D3 are equivalent. But at high doses, Vitamin D2 is less potent than Vitamin D3.

Vitamin D3: The winner in my book

If, like me, you need to take supplemental doses of Vitamin D to meet your needs. Personally, I prefer the D3 form. This is widely available and inexpensive.

I also don’t supplement on empty stomach. It turns out that Vitamin D is best absorbed with a low-to-moderate amount of fat, compared to no fat or lots of fat. Specifically, researchers have found that 11 grams of fat leads to higher absorption than either 35 grams or 0 grams, at 16% higher and 20% higher respectively. While we don’t know for sure why large amounts of fat hinder Vitamin D absorption, we do know is that the presence of some fat in a meal significantly enhances Vitamin D absorption.

Overall, I choose Vitamin D3 because of its potency and accessibility. Living in the Northeast, it’s important for me to maintain my Vitamin D levels throughout the year. When sun exposure is low and I can’t get enough from my diet, you can be sure that I am supplementing to ensure I’m getting adequate levels of this powerhouse Vitamin.

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