Benefits of Sunlight: A Bright Spot for Human Health 6

It is very clear that modern science has proven that sunlight exposure is necessary for human health. However how much sunlight exposure may not be.  M. Nathaneil Mead discusses how much sunlight exposure people should get in Part 6 of his article the Beneftis of Sunlight: A Bright Spot for Human Health.

Benefits of Sunlight: A Bright Spot for Human Health

M. Nathaniel Mead
How Much Is Enough?

Gilchrest points out a problem with the literature: “Everyone recommends something different, depending on the studies with which they are most aligned. One study reports an increased risk of prostate cancer for men with 25(OH)D levels above 90 ng/mL, for example [in contrast with the idea that more vitamin D is more protective against cancer].” In the June 2007 Lappe article, she notes, subjects in the control “high-risk” unsupplemented group had 25(OH)D levels of 71 nmol/L and the supplemented group had levels of 96 nmol/L.

Nevertheless, given the epidemiologic backdrop described above, there are now calls to rethink sun exposure policy or to promote vitamin D supplementation in higher-risk populations. Such groups include pregnant or breastfeeding women (these states draw upon a mother’s own reserves of vitamin D), the elderly, and those who must avoid the sun. Additionally, solely breastfed infants whose mothers were vitamin D deficient during pregnancy have smaller reserves of the nutrient and are at greater risk of developing rickets. Even in the sun-rich environment of the Middle East, insufficient vitamin D is a severe problem among breast-fed infants of women who wear a burqa (a traditional garment that covers the body from head to foot), as reported in the February 2003 Journal of Pediatrics.

Several recent reports indicate an increase in rickets particularly among breastfed black infants, though white babies also are increasingly at risk. A study in the February 2007 Journal of Nutrition concluded that black and white pregnant women and neonates in the northern United States are at high risk of vitamin D insufficiency, even when mothers take prenatal vitamins (which typically provide 100–400 IU vitamin D₃). Studies by Bruce Hollis, director of pediatric nutritional sciences at the Medical University of South Carolina, and colleagues suggest that a maternal vitamin D₃ intake of 4,000 IU per day is safe and sufficient to ensure adequate vitamin D status for both mother and nursing infant.

These days, most experts define vitamin D deficiency as a serum 25(OH)D level of less than 20 ng/mL. Holick and others assert that levels of 29 ng/mL or lower can be considered to indicate a relative insufficiency of vitamin D. Using this scale and considering various epidemiologic studies, an estimated 1 billion people worldwide have vitamin D deficiency or insufficiency, says Holick, who adds, “According to several studies, some forty to one hundred percent of the U.S. and European elderly men and women still living in the community [that is, not in nursing homes] are vitamin D deficient.” Holick asserts that a large number of infants, children, adolescents, and postmenopausal women also are vitamin D insufficient. “These individuals have no apparent skeletal or calcium metabolism abnormalities but may be at much higher risk of developing various diseases,” Holick says.

In the context of inadequate sunlight or vitamin D insufficiency, some scientists worry that the emphasis on preventing skin cancers tends to obscure the much larger mortality burden posed by more life-threatening cancers such as lung, colon, and breast cancers. Many studies have shown that cancer-related death rates decline as one moves toward the lower latitudes (between 37°N and 37°S), and that the levels of ambient UVR in different municipalities correlate inversely with cancer death rates there. “As you head from north to south, you may find perhaps two or three extra deaths [per hundred thousand people] from skin cancer,” says Vieth. “At the same time, though, you’ll find thirty or forty fewer deaths for the other major cancers. So when you estimate the number of deaths likely to be attributable to UV light or vitamin D, it does is not appear to be the best policy to advise people to simply keep out of the sun just to prevent skin cancer.”

To maximize protection against cancer, Grant recommends raising 25(OH)D levels to between 40 and 60 ng/mL. Research such as that described in Holick’s August 2006 Journal of Clinical Investigation article indicates that simply keeping the serum level above 20 ng/mL could reduce the risk of cancer by as much as 30–50%.

Cedric F. Garland, a medical professor at the University of California, San Diego, says that maintaining a serum level of 55–60 ng/mL may reduce the breast cancer rate in temperate regions by half, and that incidence of many other cancers would be similarly reduced as well. He calls this “the single most important action that could be taken by society to reduce the incidence of cancer in North America and Europe, beyond not smoking.” Moreover, these levels could be readily achieved by consuming no more than 2,000 IU/day of vitamin D₃ at a cost of less than $20 per year and, unless there are contraindications to sunlight exposure, spending a few minutes outdoors (3–15 minutes for whites and 15–30 minutes for blacks) when the sun is highest in the sky, with 40% of the skin area exposed.

Holick, Vieth, and many other experts now make a similar daily recommendation: 4,000 IU vitamin D₃without sun exposure or 2,000 IU plus 12–15 minutes of midday sun. They say this level is quite safe except for sun-sensitive individuals or those taking medications that increase photosensitivity.

Gilchrest says some sunlight enters the skin even through a high-SPF sunscreen, so people can maximize their dermal vitamin D production by spending additional time outdoors while wearing protection. “Without the sunscreen, this same individual would be incurring substantially more damage to her skin but not further increasing her vitamin D level,” she says.

Source: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2290997 , http://www.scribd.com/doc/6480898/Benefits-of-Sunlight-A-Bright-Spot-for-Human-Health

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Tags: breast cancer, cancer, Dr. Michael Holick, skin cancer, vitamin d, vitamin d deficiency