Are you dangerously deficient in this key nutrient?

Yesterday, I reported on the failing New York Times’ latest hit job on vitamin D. Instead of addressing the actual science on vitamin D, the report personally attacked Michael Holick, M.D., a widely respected vitamin D expert from Boston University.

I think the reporter resorted to a personal attack because the actual science on vitamin D is beyond dispute.

It seems almost every week, another new study comes out linking higher vitamin D levels with lower rates of chronic disease — including cancer and Type II diabetes — and mortality.

Despite the conclusive evidence on the importance of vitamin D, many still harbor a misplaced concern about its supposed “toxicity” when supplementing at higher levels.

But a 16-year study shows vitamin D “toxicity” isn’t a real problem. More on that study in a moment. But first, I want to put to bed some long-standing confusion regarding vitamin D’s unit of measure…

Lack of understanding about how much is “too much”

Vitamin D “toxicity” isn’t well-defined in medical literature. We don’t really know how much is “too much” vitamin D in the blood. Nor do we know if excess vitamin D actually causes symptoms.

Furthermore, most actual and rare cases of apparent “toxicity” stem from sustained, intentional ingestion of daily mega doses or incorrect dosing in children.

I’ve always thought some of the misplaced concerns about getting “too much” vitamin D stem from the use of international units (IU) as a unit of measure…

Measurements designed to confuse

Unlike other nutrients — which are measured according to  weight, or mass units, in milligrams or micrograms — vitamin D is measured according to potency with IU.

I’ve always wondered why the medical world would use this confusing, arbitrary unit of measure for vitamin D…especially when every other supplement is measured according to actual mass!

Plus, the use of IU makes the doses of vitamin D appear to be very high, when they’re really not at all. For example, I always recommend you take 10,000 IU of vitamin D daily.

Now, let’s put that amount into perspective…

Thousands of IU translate to only hundreds of micrograms. And it takes 1,000 of those micrograms to make just one milligram (and of course, milligrams are often taken by the hundreds).

Here’s how my recommended dose breaks down at-a-glance:

  • 1 International Unit = .025 micrograms
  • 1 milligram = 1,000 micrograms

So, in total:

  • 10,000 IU = 250 micrograms
  • 250 micrograms = 0.25 milligrams

As you can see, by comparison, 10,000 IU of vitamin D is not at all a large dose. It’s actually miniscule!

Few side effects even at “high” blood levels

Now let’s dive into this 16-year study, where researchers analyzed actual blood levels of vitamin D (25-hydroxy-D) levels in 73,779 men and women.

As any doctor will tell you, the vast majority of patients test normal or deficient for vitamin D levels. And concentrations rarely fall in the “high” range of what experts consider potentially “toxic.”

This study supports that observation. In fact, just 1.1. percent of the participants (780 people) had levels considered “high.” And just 0.1 percent (89 people) had levels considered “toxic.”

Furthermore, just 0.005 percent of participants showed any actual physical symptoms of excess vitamin D. (That’s only four out of 73,779 participants! Not to mention, three of those cases stemmed from incorrect dosing of liquid vitamin D.)

The researchers said potential symptoms of excess vitamin D are:

  • Abdominal pain
  • Constipation
  • Decreased appetite
  • Excessive thirst or urination

But those “side effects” sound like a walk in the park compared to the side effects of just about any prescription drug that you hear about on any night, on any channel during the “news.”

All in all, I stick with my recommendation to supplement year-round with 10,000 IU of vitamin D daily. Now, it’s available in a convenient, liquid form together with astaxanthin — a potent marine carotenoid.

Vitamin D supplementation is even more important now that we’re entering the time of the year where the sun isn’t high enough in the sky to activate natural vitamin D production in the skin.

I also recommend you ask your doctor for an annual vitamin D blood test. At about $40 a test, it’s just about the cheapest medical test you will ever take! You should aim to achieve levels between 50 and 75 nmol/L.


“Vitamin D Toxicity: A 16-Year Retrospective Study at an Academic Medical Center,” Lab Med. 2018 Mar 21;49(2):123-129