Vitamin D: Vital Role in Your Health (cont.)
"We need more food fortification [with] vitamin D," says Susan Sullivan, DSc, RD, assistant professor in the department of food science and human nutrition at the University of Maine. "We need to make it easier for people to meet their vitamin D requirements through the food supply."
Some of that fortification is already happening. In addition to milk, a growing number of food manufacturers are adding vitamin D to yogurt, breakfast cereal, margarine, and orange juice. A cup of fortified orange juice, for example, contains 100 IU of vitamin D.
Here Comes the Sun
If you're striving for Holick's recommendation of 1,000 IU a day, you may have to turn to vitamin D supplements or the sun as your vitamin D savior. Regular sun exposure can stimulate the human skin to produce quantities of vitamin D that far exceed your needs. Without a shadow of a doubt, sunlight is the largest single source of vitamin D for most people.
But before you grab the beach towel and head for the seashore, keep in mind that particularly in the higher northern latitudes, vitamin D levels can be problematic. If you live above 40 degrees north latitude -- north of Philadelphia, for example, or Denver -- you won't make much of any vitamin D in the winter.
A study at the University of Maine monitored vitamin D levels in 23 girls (ages 10-13, all residents of Bangor, Maine). In findings presented at the American Society for Bone and Mineral Research last September (2003), nearly half of these girls had insufficient levels of vitamin D in their blood in March, the time of year when levels tend to be lowest due to decreases in sunlight exposure during the winter.
"I was surprised by some of our findings," Sullivan tells WebMD. "These were healthy, active, light-skinned girls who spent a lot of time outdoors. They were eating well-balanced diets, and many were milk drinkers. So if anyone was going to have normal vitamin D status, you'd think it would be them. But their levels were quite low by March. We're in central Maine at about latitude 44 degrees north, and we don't make vitamin D in our skin for five months a year -- between November and March."
That kind of sun scarcity can take its toll on human health. "There is some striking evidence that as you go farther north, the incidence of certain kinds of cancer increases," says Sullivan. "There is more prostate and colon cancer in the north than in those who live closer to the equator."
The correlation is similar for multiple sclerosis. Research has shown the immune disorder is more common in areas with fewer hours of sunlight. For example, multiple sclerosis is more common in Canada and the northern states of the U.S. than in the southern states.
The Perils of Sun Worshiping
The sun isn't all good, of course. As any dermatologist will eagerly tell you, too much sun could risk a lot more than a bad sunburn. Routinely overdosing on sunshine could translate into life threatening skin cancer. On the other hand, if you're completely sun-phobic from sunrise to sunset, you may pay the price in the amount of vitamin D your body produces, cautions Holick, author of The UV Advantage.
So how much sun do you dare expose yourself to? Holick has calculated that if you sun yourself in a bathing suit long enough to produce slight redness of the skin, you'll produce the equivalent of 10,000-25,000 IU of oral vitamin D.
"Let's say you're on Cape Cod or a New Jersey beach in the summer," Holick tells WebMD. "Just five to ten minutes in the sun two to three times a week -- exposing your hands, legs, and arms -- is more than adequate to satisfy your vitamin D requirements, and you're not likely to significantly increase your risk of skin cancer in the process. Then after that five to ten minutes of exposure, put on a sunscreen of SPF 15 or greater for the rest of your time in the sun."
The good news is that you can't overdose on the vitamin D manufactured by your skin. But as for vitamin D in the diet and in pills, Sandon says that the upper limit is 2,000 IU a day. "Vitamin D is a fat-soluble vitamin, so it's stored in the body," she says. "If you're taking a supplement that puts your daily intake at more than 2,000 IU, you can get a toxic or overdose effect, which can possibly lead to kidney stones or kidney damage, muscle weakness, or excessive bleeding."
Published Feb. 26, 2004.
SOURCES: Michael F. Holick, MD, PhD, professor of medicine, physiology, and biophysics, Boston University Medical Center, Boston, MA. Lona Sandon, RD, assistant professor of clinical nutrition, University of Texas Southwestern, Dallas, TX. Susan Sullivan, DSc, RD, assistant professor, department of food science and human nutrition, University of Maine, Orono, Me. WebMD Medical News: "Vitamin D May Prevent MS." WebMD Medical News: "Sunshine May Lower Multiple Sclerosis Risk."
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