This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
If the name Michael Holick means anything to you, you will recall that he was asked to resign from a post in Boston University’s dermatology department in February 2004 for promoting “sensible sun exposure” in his book The UV Advantage.
Holick’s thesis—which was apparently anathema to Boston University derm department chair Barbara Gilchrest—is that most people who live in the US north of Atlanta are vitamin D deficient because one of the key sources of that vitamin is the sun. (Vitamin D is essential for the absorption of calcium and thus strong, healthy bones.) And even when the sun shines brightest, and for the longest, during the summer, we’re told to shun the sun and slather our bodies in high SPF sunscreens to defend against skin cancer.
But in doing so we might be hiking our risk for a variety of health problems including heart disease, breast cancer, and colon cancer, says Holick. "You have about a 30 to 50 percent decreased risk of developing colon, prostate, and breast cancer if you maintain adequate vitamin D levels throughout your life," Holick said in a 2007 interview with a Canadian television station.
In case you were wondering what happened to him, Holick was unbowed by his firing. (He is still at B.U., holding down a professorship in medicine, physiology and biophysics). He has kept up his advocacy of sunlight exposure, so perhaps we shouldn’t have been surprised to see a report of rickets—a disease in which the bones become softened or weakened due to vitamin D deficiency—he diagnosed in last week’s The New England Journal Medicine, almost exactly five years after he left B.U.’s dermatology department.
The report is of a mysterious case: A nine-month-old baby boy admitted to Mass General with violent seizures. A battery of tests revealed that the boy had abnormally low levels of calcium in his blood, which is known to cause seizures. A blood test then revealed Holick’s specialty: Vitamin D deficiency, which causes rickets.
The vitamin D and calcium deficiencies are related, Holick told us this week. Without enough vitamin D, the body can't absorb calcium properly. Holick says that vitamin D deficiency is very common in American babies and mothers. One of his studies looking at vitamin D levels in 40 mother-baby pairs found that 76 percent of moms and 81 percent of babies are deficient, meaning they had less than 20 nanograms per milliliter of blood. (A nanogram is one billionth of a gram).
To prevent such deficiency, Holick says pregnant women, and all adults for that matter, should be taking at least 1000 units of the sunshine vitamin a day. That means taking vitamin supplements in addition to a normal multivitamin, which typically contains only 400 units. But be advised, you can overdose on vitamin D: Taking 50,000 units per day for a long period of time can be toxic. (Holick wrote a case report about it.)
The American Academy of Dermatology (AAD), however, only recommends that kids and adults get at least 200 units of vitamin D per day either from the food or the sun. Holick says the academy's recommendations pretty much ignore research that suggests that these levels put a person at risk for heart disease, infections and various types of cancer. "They continue to have blinders on," Holick says.
A cynic might say those blinders are because the academy fears the sun. The AAD says that people should get vitamin D from a healthy diet incorporating foods naturally rich in or fortified with it, such as milk and orange juice, and/or vitamin D supplements—but not through unprotected sun exposure, which is linked to skin cancer.
"The recommendation that you should never be exposed to the sun is putting many people at risk for vitamin D deficiency," Holick says. While in the sun, it's important to cover the face but okay to expose the arms and legs for 10 minutes or so without sunscreen, he adds. "If you're going to be out in the sun for five, 10 or 15 minutes, don't be paranoid."
Image credit/NASA