Don’t take your D without the 3.

You know vitamin D is one of my Desert Island supplements, but I wanted to step back today and make sure you’re taking the right vitamin D.

Allow me to explain. According to a new study, vitamins D2 and D3 are equally successful in initially boosting the body’s vitamin D levels, but D3 is better for sustaining that boost.

In the study, 33 people were divided into three groups:

1) placebo,

2) a group that got a starting dose of D2 and then, one week later, were given D2

every day for two weeks

3) a group that got a starting dose of D3 and then, one week later, were given D3

every day for two weeks

The liver and kidneys convert both vitamin D2 and D3 into something called 25-hydroxyvitamin D, or 25OHD—which is the non-active “storage form” of vitamin D. Researchers measured the subjects’ 25OHD levels to see how the two types of vitamin D compared to one another.

The starting dose of D2 and D3 initially boosted the participants’ 25OHD amounts to similar levels. But that effect didn’t continue.

Researchers found that, over time, the gap between 25OHD levels in subjects taking vitamins D2 vs. those taking D3 started to widen, with D3 pulling ahead. Overall, they found that 25OHD levels in subjects taking vitamins D3 were 28.6 percent higher than in those taking D2.

And the levels of D2 just kept declining, while the D3 levels remained strong. In fact, the researchers commented: “the 25OHD levels in the group that received vitamin D2 declined faster than the levels in the vitamin D3 group, reaching similar levels as the placebo group at the final point.”

This study clearly shows there is a difference between vitamin D2 and D3. So while I don’t always make the distinction when I’m recommending this essential nutrient to you, rest assured, you should always look for the D3 form.

And you should, indeed, be taking it every single day. Vitamin D deficiency is startlingly common in the U.S. And it’s been linked to everything from autoimmune and heart disease to diabetes (both type 1 and type 2) and a number of cancers.

As I mentioned earlier this week, exposure to sunshine is the best way to raise vitamin D levels. But if you want to get vitamin D from the sun, you must get full mid-day sun exposure over most of your body, without sunscreen, for twenty minutes per day. (After that, go ahead and apply a non-toxic, natural, organic sunscreen.)

Even if you’re able to get direct sun exposure consistently, you should still take a vitamin D3 supplement every day. My recommendation is 5,000 IU per day minimum. I take 10,000.

And be sure to get your 25OHD level tested regularly. If it’s not between 80 and 100, increase your dose of D3 until it gets there.


“Vitamin D3 seems more appropriate than D2 to sustain adequate levels of 25OHD: a pharmacokinetic approach.” European Journal of Clinical Nutrition, epub ahead of print 3/18/15