Thursday, June 19, 2003
Jane E. Brody, NYT
International Herald Tribune
Can sunshine, now shunned by so many who fear skin cancer and wrinkles, save many more lives than it harms? Yes, says a leading expert in the field, Michael Holick, a professor of medicine, dermatology, physiology and biophysics at the Boston University School of Medicine.
Holick, who discovered the active form of Vitamin D, has pulled together an impressive body of evidence in support of his advice that no one should be, as he puts it, a "sunphobe" or, for that matter, a sun worshipper. He has concluded that relatively brief but unfettered exposure to sunshine or its equivalent several times a week can help ward off a host of debilitating and sometimes deadly diseases, including osteoporosis, hypertension, diabetes, multiple sclerosis, rheumatoid arthritis, depression, and cancers of the colon, prostate and breast.
In other words, Holick says, sunshine is good medicine. But like all medicines, the right dosage is critical to reaping the rewards that sunlight has to offer without suffering unwanted consequences.
Holick's argument that controlled exposure to sunshine can have powerful health benefits stems from decades of research into the many roles played by Vitamin D in the body. The main source of this essential nutrient is neither food nor dietary supplement. It is sunshine.
Vitamin D is made in the skin when it is exposed to the ultraviolet B rays in sunshine, and those from tanning machines. But the amount of Vitamin D formed in a given period of sun exposure depends on the color of that skin - that is, how rich the skin is in melanin, which blocks UV rays. The darker a person's skin, the longer he or she has to be in sun to form a significant amount of Vitamin D.
A U.S. study showed that 42 percent of black women ages 15 to 49 were deficient in Vitamin D by the end of winter. A very dark-skinned person may need to spend up to 50 times as much time in the sun to make the same amount of Vitamin D as someone of Scandinavian descent. For the average black person, five to 10 times as much time in the sun will be needed.
Another factor is where a person lives in relation to the equator. The farther away, the less intense one's exposure to UVB rays. This is undoubtedly why people in northern latitudes evolved with light skin, to enhance their ability to absorb UVB rays, and those near the equator evolved with dark skin, to limit that absorption to a desirable amount.
For Vitamin D to perform its myriad biochemical roles in body cells, it must first be converted into an activated form, Vitamin D hormone. For years it was thought that this process took place only in the kidneys, which then sent tiny amounts of the hormone to the circulatory system for delivery to other tissues.
But studies by Holick and others have shown that the cells in many different organs do not have to rely on the meager supply of Vitamin D hormone from the kidneys. Rather, cells in other tissues, including the prostate, breast, colon and immune system, are also able to convert Vitamin D into the active hormone.
Vitamin D is critical to the formation and maintenance of normal bones. Even if people consume enough calcium, they cannot build and maintain bone mass if they are deficient in Vitamin D. One symptom of Vitamin D deficiency is pain and weakness in the muscles and bones. Based on that symptom, Holick has suggested that some disorders diagnosed as fibromyalgia may in fact be Vitamin D deficiency.
Holick noted a recent resurgence of rickets in the United States, the combined result of exclusive breast-feeding (breast milk has almost no Vitamin D) and keeping babies out of the sun or slathered with sunscreen. A sunscreen with an SPF of 8 blocks 95 percent of the skin's ability to make Vitamin D, and an SPF of 15 blocks 99 percent. In the prostate, the Vitamin D hormone has been shown to be an inhibitor of abnormal cell growth, and cells in the colon and breast have similar mechanisms for using this hormone.
A Scandinavian study linked low levels of Vitamin D in the blood to a risk of developing prostate cancer that is about 50 percent higher than it is for those with normal and high levels. And in eight years of research conducted in a Baltimore study of aging, experts found that those with low levels of circulating Vitamin D had a 50 percent greater risk of developing colon cancer than those with normal to high levels.
William Grant of the National Aeronautics and Space Administration reported that people who worked outdoors or lived in sunny climates had lower death rates from cancers of the breast, colon, prostate, ovary, bladder, uterus, esophagus, rectum and stomach.
The same applies to such autoimmune diseases as multiple sclerosis, rheumatoid arthritis and type 1 diabetes, which is usually diagnosed in children and young adults.
How much Vitamin D is enough? Although the official recommended amount
ranges from 200 international units for infants to 600 for the elderly,
Holick and other experts say 1,000 units a day are needed, an amount that
few people consume through foods or supplements. Sunshine must fill in
Copyright © 2003, The New York Times