They don’t go nearly as far as the ‘60s surf rockers who sang “I Live for the Sun,” “Fun in the Sun” and “Sun Tan Baby.”
Still, researchers are beginning to conclude that modest exposure to unprotected sunlight may actually be good for you, helping the body produce the vitamin D it needs to keep bones healthy and ward off cancers.
Until recently, the common assumption was that Americans have been getting all the vitamin D they needed since the U.S. government began requiring dairy producers to fortify milk with the vitamin in the 1930s.
Studies since 2003, however, have shown that most Americans are actually undernourished in vitamin D, a substance that our bodies synthesize when exposed to the sun’s ultraviolet B waves -- the same ones that cause sunburn. Thus vitamin D’s nickname, the “sunshine vitamin.”
Meanwhile, the evidence of vitamin D’s curative efficacy has continued to mount. In the last few months, studies have suggested it might reduce the risk of lymphoma and, ironically, skin cancer and that it might improve the survival rate for lung cancer.
Now two studies show that vitamin D might help the body fight prostate cancer and premenstrual syndrome.
In the prostate cancer study, researchers at three cancer centers compared 450 patients with advanced prostate cancer with 455 men who didn’t have the disease. Men with high sun exposure had half the risk of prostate cancer than did men with low sun exposure.
The researchers, who focused on gene receptors in the prostate gland, say that the amounts of vitamin D were the crucial factor, said Sue Ingles, an assistant professor of preventive medicine at USC’s Keck School of Medicine and a coauthor of the study, published in the current issue of the journal Cancer Research.
“Since the body can make vitamin D on its own with sunlight, we believe our findings are significant,” Ingles said. “Prostate cancer is the most common non-skin cancer among American men, with about 230,000 new cases and 30,000 deaths each year, and there are few known causes for it.”
In the second study, researchers at the University of Massachusetts compared the diets of 1,057 women with PMS with the diets of 1,968 women reporting no PMS. The decade-long study showed that high levels of vitamin D and calcium appeared to significantly lower women’s risk of premenstrual syndrome.
Previous studies had suggested that calcium supplements and vitamin D, which helps the body absorb calcium, may reduce the severity of PMS. The new study, however, published in the June 14 edition of the Archives of Internal Medicine, is the first to suggest that calcium and vitamin D may help prevent the initial development of PMS.
Lead researcher Elizabeth R. Bertone-Johnson said clinicians should consider using vitamin D as an alternative to stronger medications commonly prescribed for PMS, such as antidepressant drugs, which can have substantial side effects.
Both studies contribute to growing discussions about how much vitamin D Americans need -- and about where they should get it.
Researchers are divided on how to weigh the risks and benefits of sun exposure.
Harvard Medical School professor Edward Giovannucci has drawn fire for saying that public health officials spend too much time scaring Americans away from the sun.
In an April speech to the American Assn. for Cancer Research, he acknowledged the dangers of the sun-related skin cancer melanoma, which was diagnosed in 55,000 Americans last year, killing 7,900. But, he argued, too little sun, and therefore too little vitamin D, may cause 70 other cancer deaths per 100,000 people each year.
“I would challenge anyone,” Giovannucci said during the speech in Anaheim, “to find an area or nutrient or any other factor that has such consistent anticancer benefits as vitamin D.”
However, David E. Sawcer, a USC dermatology professor, suggests a measured approach to vitamin D exposure.
“Though moderate sun exposure has to be helpful, there is no metabolic benefit in sunburn,” he said. “Admittedly, it may not be that easy to decide what moderation is, but you can judge what excess is. Sunburn is useless.”
Sunshine, of course, isn’t the only way to boost your body’s vitamin D levels to the FDA’s recommended daily allowance of 200 international units (IU) for adults up to age 50, 400 IU for adults 51 to 70 and 600 IU for those 71 and older. An eight-ounce serving of milk provides 100 IU of vitamin D.
The fat-soluble vitamin is also abundant in mackerel, sardines and cod liver oil, the last of which contains 1,360 IU in one single, if harrowing, tablespoon.
In Southern California, however, that daily allowance can be met in just a few minutes for fair-skinned people, with adjustments made for age and skin tone, says Sawcer.
Younger people need less vitamin D, while people with dark skin need more sun time to manufacture vitamin D because the pigment in skin blocks ultraviolet rays. For example, African Americans need six to 10 times more sun exposure for vitamin D synthesis than people with fair skin.
Because there are so many variables, people should just use common sense, Sawcer said. “Walk your dog in the morning. Stand in the shade at noon. In California, you have to be particularly careful in summer,” he said.