A Neglected Nutrient

Are Americans Dying From a Lack of Vitamin D?

Of all the medical orthodoxies of recent years, few were as ironclad as the prohibition against sunbathing. In a triumph of public education, the notion of a "healthy tan" was turned on its head, as conditions ranging from wrinkles to cataracts, immune-system problems and skin cancers, including deadly malignant melanoma, were linked to ultraviolet exposure. But in the last decade or so researchers have begun asking whether something was lost in the process: the often-overlooked substance that occurs naturally in some foods, especially fish, but is most efficiently produced in the body by exposure to sunlight--vitamin D.

It is best known as an essential nutrient for calcium uptake; rickets, a childhood disease that deforms bones, was largely vanquished decades ago by adding vitamin D to milk. But vitamin D may be just as important at the other end of life, where a deficiency has been associated with osteoporosis, rheumatoid arthritis and certain cancers. And studies show that even among otherwise healthy young adults, vitamin D deficiency is endemic--especially in northern latitudes at the end of the winter, when the body has used up what it made and stored during the sunny months. It's a particular problem for dark-skinned Americans, whose protective pigmentation evolved for life near the equator. "I don't like to overstate things," says Dr. Robert Heaney, a vitamin D researcher at Creighton University, "but I think we may find that vitamin D deficiency is a public-health crisis."

The most intriguing findings relate to cancer, a line of research that began 25 years ago with the discovery that colon cancer was twice as common in the Northeast as in the sun belt. There are also hints that vitamin D may help prevent breast, prostate and ovarian cancers by slowing the division of cells. The National Institutes of Health Web site warns that more research is needed to determine whether people with normal vitamin D levels can protect themselves by taking more, adding that "it is premature to advise anyone to take vitamin D supplements for cancer prevention." But the scientists who actually study the nutrient aren't waiting for more results. "I've been studying D for more than 30 years," says University of Toronto biochemist Reinhold Viet, "and the remarkable thing is, this actually works. My jaw drops as to why isn't everybody doing this. It drives me nuts."

Vitamin D also seems to play a role in autoimmune diseases, including multiple sclerosis--which, like colon cancer, is more common at higher latitudes. A large study of women nurses found that those who took multivitamins including D lowered their risk of MS by 40 percent. And the Iowa Women's Health Study of nearly 30,000 women in their 50s and 60s found that rheumatoid arthritis, another autoimmune condition, went down as dietary vitamin D increased. Unsurprisingly, vitamin D seems to protect against osteoporosis and osteomalacia, a related condition that can cause chronic pain throughout the body. And Vieth's research even suggests that vitamin D can improve mood and may help relieve symptoms of depression.

His prescription, which is echoed by many other researchers, is for a substantial increase in the amount of Vitamin D most of us get: 1,000 international units a day, or five times the recommended dietary (or daily) allowance. (The RDA for adults older than 50 is higher.) Vitamin D at those levels is safe, readily available and relatively inexpensive. Even cheaper, of course, is sunlight, which is why Dr. Michael Holick, director of the Vitamin D, Skin and Bone Research Laboratory at Boston University, recently wrote a book promoting the health benefits of moderate sun exposure--a position that led to his resignation from the dermatology department. "Yes, a few people have called me nuts," Holick admits. "But every tissue and cell in the body requires vitamin D, and most of the population is at risk for deficiency. It has enormous consequences for overall health."