A massive misunderstanding regarding vitamin D recommendations has led people to mistakenly believe they are deficient in the vitamin, according to a commentary published Thursday in the New England Journal of Medicine (NEJM).
And that means too many people are taking vitamin D supplements that they don’t need — and that may cause them harm.
The doctors who wrote the NEJM commentary know what they’re talking about. Several of them — including the commentary’s lead author, Dr. JoAnn Manson of Harvard Medical School — are members of the committee at the Institute of Medicine (now called the Health and Medicine Division of the National Academies of Sciences, Engineering and Medicine) that is responsible for setting the recommended dietary allowance (RDA) for vitamin D.
The source of the confusion
How did the misunderstanding come about? It starts with the fact that individuals vary significantly in how much vitamin D (or any vitamin) they need. In 2011, the IOM determined that healthy people (those who do not have a specific medical condition that causes a vitamin D deficiency) require, on average, 400 international units (IUs) of vitamin D per day — until they reach the age of 71, when they require, on average, 600 IUs per day.
But to ensure that everybody gets enough of the nutrient, the IOM set the RDA for vitamin D at amounts that reflect the upper end of the distribution of the biological requirement — in other words, at the highest amount that any healthy person would need: 600 IUs per day for people aged 1 through 70, and 800 for those 70-plus.
And that’s where the confusion sets in. Most people believe the RDA for vitamin D — and its corresponding blood levels — represents the cut-off point for what is “healthy” and what isn’t. Yet, as Manson and her colleagues point out in the commentary, that interpretation is wrong, as almost everyone actually needs less than that amount.
In fact, only 13 percent of Americans aged 1 to 70 are at risk of being deficient in vitamin D — and less than 6 percent are deficient. “These levels of deficiency do not constitute a pandemic,” write Manson and her colleagues.
Too much screening
Nor do those levels support routine vitamin D screening. The commentary’s authors say that people should not have their blood levels of vitamin D tested unless bone loss is strongly suspected and specific risk factors, such as being in a nursing home or taking prescription drugs that interfere with vitamin D metabolism, are present.
“Universal screening based on inappropriate cut points might lead to routine supplementation in generally healthy populations with adequate vitamin D levels,” they write.
“A preferable option,” they add, “would be to encourage patients and the public to choose foods containing, or fortified with, vitamin D — an approach that will be facilitated by new regulations requiring that vitamin D content be listed on nutrition labels.”
One measuring cup of fortified milk contains, for example, 115 to 124 IUs of vitamin D, while three ounces of cooked salmon contains 447 IUs.
And then there’s the sun. Five to 30 minutes of sunlight exposure on the face, arms or legs between 10 a.m. and 3 p.m. twice a week is usually enough to meet most people’s vitamin D needs — including those living in Minnesota and other northern latitudes, according to experts.
Yet, as the Associated Press (AP) reports, Americans — particularly older ones — continue to fret about not getting enough vitamin D and are undergoing screening for vitamin D deficiency in growing numbers.
“Under Medicare, there was an 83-fold increase from 2000 to 2010, to 8.7 million tests last year, at $40 apiece,” writes AP reporter Marilyn Marchione. “It’s Medicare’s fifth most common test, just after cholesterol levels and ahead of blood sugar, urinary tract infections and prostate cancer screening.”
The use of vitamin D supplements has also skyrocketed, from 5 percent of Americans in 1999 to 19 percent in 2012, Marchione adds.
First, do no harm
As I’ve noted here before, there is no scientific consensus that such supplementation leads to positive health outcomes, including the prevention of bone fractures.
What experts do agree on, however, is that vitamin D supplementation in people who don’t need it can be harmful. Excess vitamin D can cause calcium to build up in the blood, leading to fatigue, nausea, constipation, headaches and other symptoms.
Megadoses of the vitamin can also contribute, over time, to the development of kidney problems.
For more information: You can download and read the NEJM commentary on the journal’s website.