Summer Sun Helps Reverse Winter Vitamin D Deficiency

As summer heats up and people across America start slathering on the sunscreen, a note of caution is in order—a little sunshine is good for you.

Studies increasingly are suggesting the value of vitamin D—often known as the sunshine vitamin, because that’s one way you can obtain it—in everything from bone metabolism to maintaining muscle strength, immune function, reducing hypertension and possibly even playing a role in prevention of cancer and autoimmune disease.

Summer is a time when most people finally get enough of this vitamin due to their sun exposure, and also help build stores of it in their fat for use during the dark days of winter. But research has suggested that, for whatever reason, as many as a billion people around the world may now be vitamin D deficient, posing possibly serious threats to their health.

“The old theory was that if you had enough vitamin D to prevent rickets and osteomalacia—two skeletal disorders—you were okay,” says Victoria Drake, a research associate in the Linus Pauling Institute at Oregon State University, and manager of its Micronutrient Information Center. “But new research now is raising our awareness about the possible relationships between vitamin D and cancer, particularly colorectal, breast, ovarian and prostate cancers. There also are potential links to cardiovascular disease and autoimmune diseases such as multiple sclerosis and rheumatoid arthritis.”

Many of the studies are observational, Drake says, and more work needs to be done with randomized, double-blind, placebo-controlled clinical trials. This means that experts are still arguing about how much vitamin D is enough. Some feel that the optimal amount is several times higher than the adequate intake level set by the Food and Nutrition Board of the Institute of Medicine, which is 200 international units (IUs) per day for adults ages 19-50.

What’s clear, however, is that many Americans are not getting even those minimal amounts, especially those with dark skin colors—in fact, one study reported that 42 percent of African American women were vitamin D deficient.

As a result, Drake says, many doctors are increasingly starting to test their patients for deficiency of this vitamin, especially in the temperate zones above 40 degrees latitude—a line running roughly from Philadelphia to Denver and through Northern California. That includes New York City, Boston, Chicago, Detroit, Seattle and many other highly populated cities. Residents of the Pacific Northwest, with its northern latitudes and eternally cloudy winters, are especially vulnerable.

“My own doctor said that he frequently tests for vitamin D status, and that vitamin D deficiency is prevalent in his patient population,” Drake says. “Experts are now talking about a phenomenon they call ‘Vitamin D Winter.’”