A Walmart ad in my local newspaper trumpets “75% of all Americans don’t get enough Vitamin D” and offers to sell me Maximum Strength Vitamin D3, 5000 IU capsules to “promote bone, colon and breast health.” Meanwhile, the Institute of Medicine (IOM) tells me that “the majority of Americans and Canadians are receiving adequate amounts of … vitamin D” and that no one should take more than 4000 IU a day.  Apparently Walmart and the IOM aren’t talking to each other.

The media have been giving the impression that vitamin D is a new wonder drug. They have told us that we aren’t getting enough sunlight, that a large percentage of us suffer from vitamin D deficiency, and that low levels of vitamin D are associated with cancer, multiple sclerosis, peripheral vascular disease, diabetes, rheumatoid arthritis, Parkinson’s and Alzheimer’s disease, and other conditions. Low levels of vitamin D have been linked to higher overall mortality (but so have high levels of vitamin D!). The anti-vaccine folks have been telling us (without any controlled studies) that vitamin D supplements are better than vaccines for preventing influenza. There’s no good evidence that raising vitamin D levels with supplements actually prevents any of these conditions, but many people think it should, and doctors have increasingly been measuring blood levels and prescribing high dose supplements. Is this just another passing fad like the enthusiasm for vitamin C, or are we belatedly recognizing a serious deficiency problem?

I’ve had a lot of inquiries about “is this information trustworthy?” and “how much vitamin D should I be taking?” I’ve been telling people that I didn’t know, that recent findings will soon result in new recommendations, and I’ve been eagerly awaiting the new guidelines. Now we have them, thanks to the IOM. They are not what most of us anticipated. Since so many doctors had been advocating higher levels to prevent things like cancer, I thought official recommended intake levels would go up; instead, they went down.


The IOM was asked by the US and Canadian governments to assess the current data on health outcomes associated with calcium and vitamin D. They formed a committee of experts who did an exhaustive review of over 1000 studies and listened to testimony from scientists and stakeholders. Their report, issued on 11/30/2010, concluded that the evidence supported a role for these nutrients in bone health but not in other health conditions, that the majority of the American and Canadian population is getting enough of both vitamin D and calcium, and that there is emerging evidence that an excess of these nutrients may be harmful. Based on that evidence, they established new Dietary Reference Intakes (DRIs) for vitamin D and calcium. They acknowledged exceptions and areas of uncertainty.

A couple of my correspondents have been screening their patients for vitamin D deficiency and they report that at least half fall in the “very low” category <20ng/mL. Doctors are giving large doses (often a weekly 50,000 IU pill for several weeks) to quickly get their patients back into the “normal” range. Then a 2000 IU or even a 5000 IU daily dose can be necessary to keep them at that level. Are they treating a true deficiency? Or are they uselessly trying to move people from one side of a normal bell curve to the other? When half of our patients fall into the “abnormal” category, it bothers me.

The IOM report explains

the measurements, or cut-points, of sufficiency and deficiency used by laboratories to report results have not been set based on rigorous scientific studies, and no central authority has determined which cut-points to use. A single individual might be deemed deficient or sufficient, depending on the laboratory where the blood is tested. The number of people with vitamin D deficiency in North America may be overestimated because many laboratories appear to be using cut-points that are much higher than the committee suggests is appropriate.

There can be too much of a good thing. Gary Null inadvertently sounded a note of caution when he managed to poison himself with one of his own products.  The manufacturer of Null’s Ultimate Power Meal supplement got the math wrong (by a factor of a thousand, no less!) and overloaded the supplement with 2,000,000 IU of vitamin D instead of 2000 IU. Null nearly died. The IOM recommends an upper limit of 4000 IU a day.

Calcium supplements, long recommended to prevent osteoporosis, have been associated with heart attacks in postmenopausal women, but only in those who took it without the recommended addition of vitamin D. There are concerns that excess calcium might cause kidney stones and other adverse effects. The IOM found that most people get enough calcium from their diet, with the exception of girls ages 9-18, and that postmenopausal women who take supplements may be getting too much calcium. Once intakes exceed 2000 mg a day, the risk for harm increases.

This table shows the new recommendations for calcium and vitamin D for different age groups. 

As we continue to learn more about nutrition, the DRIs will continue to change. Science is a work in progress. The IOM has not given us a final answer, but it has offered reasonable science-based interim guidance. I’ll take its advice over that of Walmart any day!

Posted by Harriet Hall

Harriet Hall, MD also known as The SkepDoc, is a retired family physician who writes about pseudoscience and questionable medical practices. She received her BA and MD from the University of Washington, did her internship in the Air Force (the second female ever to do so),  and was the first female graduate of the Air Force family practice residency at Eglin Air Force Base. During a long career as an Air Force physician, she held various positions from flight surgeon to DBMS (Director of Base Medical Services) and did everything from delivering babies to taking the controls of a B-52. She retired with the rank of Colonel.  In 2008 she published her memoirs, Women Aren't Supposed to Fly.