USA: The sunshine D-lemma

. September brings the end of summer in the Northern hemisphere and, for many, that means getting less sunshine. That might be a plus for our skin, but it’s not so great when it comes to vitamin D. Our skin uses the sun’s rays to make vitamin D, and research is showing that vitamin D plays an important role in the prevention of several diseases. HEALTHbeat explains how to get adequate vitamin D, writes Nancy Ferrari, Managing Editor of Harvard Health Publications. BOSTON, MA (Harvard Medical School - HealthBeat), September 2, 2008: Using sunscreen and avoiding the midday sun are mainstays of skin cancer prevention. However, many vitamin D researchers believe that by diligently shielding ourselves from sunlight we might be missing out on the many benefits of this powerhouse vitamin, which is made when our skin is exposed to ultraviolet light. Ultraviolet B (UVB) rays cause sunburn and the cell damage that leads to skin cancer, although research implicates ultraviolet A (UVA) rays as well. But it’s the energy from UVB that penetrates the skin and eventually becomes the biologically active form of vitamin D. Active vitamin D helps regulate how cells grow and mature, so in some circumstances it may put the brakes on cancerous runaway cell growth. Vitamin D also helps keep the immune system in line, which may be the reason animal and epidemiological studies hint at a connection between low vitamin D levels and autoimmune disorders such as type 1 diabetes and multiple sclerosis. Fortunately, a sizable patch of middle ground exists between the two camps that acknowledges the dangers of sun exposure while giving vitamin D its due. The winter filter During the winter in the upper latitudes (roughly 40° — the latitude of New York City — or higher) of the Northern and Southern hemispheres, sunlight hits the earth at an angle, so it travels a longer distance through the atmosphere. Much, if not all, of the UVB gets filtered out (although the longer waves of UVA still get through). Sunburn isn’t a problem, but blood levels of vitamin D drop to about half of their summertime levels. Apart from the risk of UVB, added sun exposure won’t fix many people’s vitamin D woes. With age, the skin’s capacity for making vitamin D diminishes, so the effect of getting more sun is going to be limited in older folks. And the melanin that makes skin dark effectively filters out UVB, so African Americans are much more likely than whites to have low levels of vitamin D. Researchers in sun-drenched Arizona reported in 2008 that over half of the African Americans in their colorectal cancer study had low vitamin D levels, defined as 20 nanograms per milliliter (ng/ml). Diet and supplements Government guidelines say people between the ages of 51 and 70 should get 400 International Units (IU) of vitamin D daily, and those ages 71 and older, 600 IU. Many experts say Americans should shoot for 1,000 IU, because, on average, that’s how much it takes (along with incidental sun exposure) to get the levels in the blood to 30 ng/ml, the level at which prevention of cancer and other diseases seems to kick in. Unfortunately, there are only a few good food sources of vitamin D: salmon (about 350 IU per 3½-ounce serving), mackerel, sardines, and other kinds of oily seafood are about it. In the U.S., milk and some brands of orange juice are artificially fortified with 100 IU per 8 ounces. Some breakfast cereals are also fortified. Traditionally, supplement makers have used vitamin D2 (ergocalciferol), particularly in multivitamin pills. Some data show little difference in the effects of D2 and D3 (cholecalciferol), the form used to fortify milk and contained naturally in fish, but the conventional wisdom has been that D2 is about a third to a fourth less effective than D3 at increasing blood levels of vitamin D. Because D3 has been presumed to be more potent, it is increasingly the form used in vitamin D and vitamin D-calcium supplements. You can get too much vitamin D, but the level where toxicity is seen is almost certainly many times higher than the upper daily limit of 2,000 IU set by the Institute of Medicine. For years, vitamin D researchers have wanted a re-evaluation of vitamin D minimums and maximums, but so far, this hasn’t happened. For the latest information on vitamins and your health, order Special Health Report, Vitamins and Minerals: What you need to know, at www.health.harvard.edu/VM. Copyright 2008 by Harvard University.