D e s e r t E x p o s u r e
June 2008
Here Comes the Sun
Balancing the risks of sun exposure against the benefits of the "sunshine vitamin."
By David A. Fryxell
If it's summer in sunny New Mexico, it must be time to slather on the sunscreen. The typical view of that deceptively, well, sunny object whose rays strike us so strongly in the Land of Enchantment was summed up last month in an Albuquerque Journal article: It quoted an Albuquerque dermatologist as essentially arguing that there's no such thing as "safe" sun exposure. And it's not just here in sunny New Mexico that the seasonal warnings have again gone out; a recent news release from the Skin Cancer Foundation urges, "Use a sunscreen of SPF 15 or higher whenever you are outdoors."
While no one thinks getting a sunburn is a good idea, a growing body of scientific evidence suggests that sunlight might not be quite the pure evil that some dermatologists demonize. Hardly a month passes without some new scientific journal article reporting yet another benefit of vitamin D — the so-called "sunshine vitamin" that your body can synthesize naturally in the presence of (shudder!) sunlight. That steady drumbeat of good news about vitamin D has led some experts to suggest that a little bit of sun — 10 to 15 minutes a day of unprotected exposure — might actually be good for you.
Which only makes sense, if you think about it. Our ancestors, after all, somehow survived before the invention of sunscreen. And the human body probably wouldn't have evolved the ability to make its own vitamin D if there weren't some health benefits.
But can't you get plenty of vitamin D from your diet, without exposing yourself to that ol' debbil Sol? The fact is, dietary sources of vitamin D are few and far between, and it's hard to get adequate amounts — much less the higher levels that some studies now show you might need to enjoy vitamin D's full health benefits — from diet alone.
Current recommendations for vitamin D intake range from 200 International Units (IU) for people age 50 and younger to 400 IU for ages 51 to 70 and 600 IU for ages 71 and above. But an editorial in the American Journal of Clinical Nutrition last year pointed out, "The balance of the evidence leads to the conclusion that the public health is best served by a recommendation of higher daily intakes of vitamin D." A 15-member expert panel came to much the same conclusion, also in 2007.
Studies of bone-fracture risk have found that intake levels of vitamin D — an essential complement to calcium for building strong bones — of 700 to 800 IU are required for an appreciable reduction in fracture risk. Dr. Edward Giovannucci, a professor of medicine and nutrition at Harvard who's studied vitamin D's cancer-fighting potential, has said that the optimal level may be as high as 1,500 IU daily.
An eight-ounce glass of fortified milk or juice, however, contains only about 100 IU of vitamin D. Other dietary sources of vitamin D include fortified breakfast cereals, oily fish such as salmon, mackerel, herring and sardines, and cod-liver oil, the bane of a generation of children.
It was cod-liver oil, in fact, that led to today's recommendations for vitamin D intake, which Bruce Hollis, a professor of pediatrics, biochemistry and molecular biology at the University of South Carolina, argues are outdated and based on slim research. Hollis told the Washington Post, "Fifty years ago, a bunch of guys got in a room and said, 'We know that a teaspoon of cod-liver oil cures rickets in a child and it has 400 IU of vitamin D.' They transposed that amount onto adults."
If cod-liver oil isn't to your taste and you don't want to drink 8 to 15 glasses of fortified milk every day, you can also get vitamin D from dietary supplements. Most vitamin D experts advocate supplements as well as sun exposure, while cautioning that standard multivitamins contain only modest amounts. Don't overdose on multivitamins just to boost your vitamin D: You can find Vitamin D supplements that deliver 400 to 800 IU. Make sure, however, that you're buying the more potent form, vitamin D3 (cholecalciferol), rather than D2 (ergocalciferol); D3 may be as much as three times as effective in raising blood levels of vitamin D.
Or you can spend a few unprotected minutes in the New Mexico sun. And we do mean only a few — lest you add to those scary statistics of 1 million cases of skin cancer and 7,700 deaths from melanoma annually. In a fair-skinned person, a mere 15 minutes of unprotected sun exposure at midday is enough to generate a whopping 20,000 IU of vitamin D, which the skin makes from cholesterol when exposed to ultraviolet light. Unlike vitamin D in pill form — where the daily safe upper limit is 2,000 IU (although many experts argue that should be raised to 10,000 IU) — there's no health risk from too much of the body's natural vitamin D.
Not surprisingly, dark-skinned people and those in far-northerly climes that are shy on sunshine are more likely to be vitamin-D deficient. As far back as 1960, scientists noticed that those same people — African-Americans and Scandinavians, in this case — were also most likely to die of prostate cancer. More recent research has found a similar link with colorectal adenomas — benign tumors that can lead to cancer, as well as the incidence of breast cancer.
But that's only the start of the story. Low levels of vitamin D have been associated with a greater risk of pancreatic cancer. In February 2005, two epidemiological studies published in a single issue of the National Cancer Institute's Journal suggested that sunlight may reduce the risk of non-Hogkin's lymphoma and may be associated with improved survival rates in patients with — of all things — early-stage melanoma. (Indeed, people who work outdoors actually have less incidence of melanoma than do indoor workers. That difference is usually attributed to tanning from regular sun exposure, reducing the risk of sunburn that's known to lead to this deadliest skin cancer. Or it may be simply that all that time outdoors boosts natural levels of vitamin D, which in turn has cancer-fighting properties.)
And last fall, scientists at the University of California-San Diego (UCSD) published results of a study comparing breast and colon cancer rates with average wintertime vitamin D levels in 15 countries, including the US. Their analysis found that cancer rates tend to fall with higher vitamin D levels. In late winter, lacking adequate sunshine to boost the body's natural vitamin D factory, Americans average 15-18 nanograms per milliliter (ng/mL) of vitamin D in the blood. The researchers estimated that at levels of at least 55 ng/mL, 85,000 cases of breast cancer and 60,000 of colon cancer could be prevented annually in the US.
(For comparison, about 62,500 cases of melanoma are diagnosed annually in the US. Mysteriously, despite Americans' widespread adoption of sunscreen and avoidance of the sun, incidence of melanoma is rising faster than almost any other type of cancer. From 1950 to 2004, a period in which Americans headed inside in droves, the mortality rate of melanoma doubled.)
The UCSD study found that average US adult intake of vitamin D is only 230 IU daily. To achieve significant reductions in cancer risk, researchers suggested, daily intake would have to reach 2,000 to 3,500 IU. Lead author Cedric F. Garland noted, "This could be best achieved with a combination of diet, supplements and short intervals — 10 or 15 minutes a day — in the sun."
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