The air is getting colder, the days are getting longer, and Starbucks has already unveiled this year’s holiday cups, which means one thing: It’s vitamin-D season. This is the time of year when people bust out the sun lamps in an attempt to ward off a wintertime deficiency.
To be fair, we all need the D, as one wonderfully misguided Canadian ad campaign put it — it’s a key element of bone growth, and a lack of it has been linked to depression and heart disease, among other things. But according to a paper published last week in the New England Journal of Medicine, your stress about it is likely misplaced: In general, we’re way, way overestimating how much we actually need.
“The claim that large proportions of North American and other populations are deficient in vitamin D is based on misinterpretation and misapplication of the Institute of Medicine reference values for nutrients,” the authors wrote. As the Associated Press explained:
People vary, biologically, in how much of any vitamin they need. The institute’s experts estimated the requirement by comparing various intake and blood levels with measures of bone health. They estimated that, on average, people need about 400 international units of vitamin D per day, and 600 for people older than 70.
To ensure that everyone gets enough, they set the RDA at the high end of the spectrum of the population’s needs — 600 to 800 units, depending on age. So, by definition, nearly everyone’s true requirement is below that.
By this definition, “less than 6 percent of Americans ages 1 to 70 are deficient and only 13 percent are in danger of not getting enough,” the AP reported. Even so, a vitamin-D deficiency test is now the number-five most common test ordered under Medicare: “There was an 83-fold increase from 2000 to 2010, to 8.7 million tests last year.” And nearly a fifth of all Americans were taking vitamin-D supplements in 2012, up from 5 percent in 1999.
This last part isn’t all bad — because your body produces vitamin D when your bare skin is exposed to sunlight, supplements can be an effective way of making up for the fact that you spend most of the winter bundled up (and therefore shielded from the sun). So can a diet rich in vitamin-D-heavy or fortified foods, like fish or milk.
The risk is in overdoing it: “There’s potential long-term risk in constantly saturating our bodies with way more than we actually need,” Catherine Price, the author of Vitamania, told Science of Us in an interview last year. A vitamin-D deficiency is a problem, but so is a surplus: Too much can cause health issues from queasiness to kidney stones. The bottom line: Pay attention to how much you’re getting from food, pop a supplement if your diet alone doesn’t cut it, and otherwise don’t stress. Odds are you’re probably doing just fine.