Vitamin D: Vital Role in Your Health
Researchers conclude the 'sunshine vitamin' is good medicine.
By Richard Trubo
WebMD Weight Loss Clinic - Feature
Reviewed By Brunilda Nazario, MD
Vitamins like C and E continue to be the darlings of many supplement lovers. But those vitamin superstars are being forced to share their throne with the long neglected vitamin D, which is finally getting the attention it may have always deserved.
No doubt, you're probably familiar with the role of vitamin D in promoting healthy bones, largely by promoting the absorption of calcium. "If you have a vitamin D deficiency, particularly in your older years, it can lead to osteoporosis or osteomalacia [bone softening]," says Lona Sandon, RD, assistant professor of clinical nutrition at the University of Texas Southwestern in Dallas.
But there is recent and mounting evidence that links low levels of the vitamin to an increased risk of type 1 diabetes, muscle and bone pain, and, perhaps more serious, cancers of the breast, colon, prostate, ovaries, esophagus, and lymphatic system.
If you want to lower your blood pressure, vitamin D may be just what the doctor ordered. If you're trying to reduce your risk of diabetes, or lower your chances of heart attacks, rheumatoid arthritis, or multiple sclerosis, then vitamin D should be at the front of the line in your daily supplement regimen.
D-fense for Your Health
As the research into vitamin D is accumulating, it's hard to know where the accolades should start. "Activated vitamin D is one of the most potent inhibitors of cancer cell growth," says Michael F. Holick, PhD, MD, who heads the Vitamin D, Skin, and Bone Research Laboratory at Boston University School of Medicine. "It also stimulates your pancreas to make insulin. It regulates your immune system."
Just consider these recent studies:
- At Boston University, after people with high blood pressure were exposed to UVA and UVB rays for three months, their vitamin D levels increased by more than 100% -- and more impressively, their high blood pressure normalized. "We've followed them now for nine months, and their hypertension continues to be in remission," says Holick, professor of medicine, physiology and biophysics at Boston University. One theory about how vitamin D reduces blood pressure: It decreases the production of a hormone called renin, which is believed to play a role in hypertension.
- In a study published in the Journal of the American Medical Association in December 2003, of more than 3,000 veterans (ages 50 to 75) at 13 Veterans Affairs medical centers, those who consumed more than 645 IU of vitamin D a day along with more than 4 grams per day of cereal fiber had a 40% reduction in their risk of developing precancerous colon polyps.
- In a report in the Journal of the American Geriatrics Society in February 2004, researchers at the University of Basel in Switzerland showed that elderly women who took a vitamin D supplement plus calcium for three months reduced their risk of falling by 49% compared with consuming calcium alone. Those women who had fallen repeatedly in the past seemed to gain the most benefit from vitamin D.
- A study in the Jan. 13, 2004 issue of Neurology indicated that women who get doses of vitamin D that are typically found in daily multivitamin supplements -- of at least 400 international units -- are 40% less likely to develop multiple sclerosis compared with those not taking over-the-counter supplements.
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Many vitamin D researchers are convinced the government's recommendations for adequate vitamin D intake are far below what your body really needs. Those guidelines call for 200 IU a day up to the age of 50, 400 IU from 51 to 70, and 600 IU over age 70.
But, says Holick, studies show that to achieve blood levels of vitamin D that can protect you against chronic diseases, you need an optimal dose of 1,000 IU of vitamin D a day. The vitamin is well absorbed from foods like fortified milk and from vitamin pills, whether taken alone or in combination with other foods.
So how can you get enough of this overlooked vitamin? Most foods aren't filled to the brim with vitamin D -- far from it. You can get 425 IU in a 3-ounce serving of salmon, and 270 IU in 3.5 ounces of canned sardines. But most foods provide much more modest amounts of vitamin D, from egg yolks (25 IU per egg) to cheddar cheese (2.8 IU per ounce).
"You'll get 200 IUs of vitamin D by drinking two glasses of fortified milk," says Sandon, spokeswoman for the American Dietetic Association. But at age 70, even reaching the government's recommended level of 600 IU from diet alone can be a challenge. "These people are probably not drinking six glasses of milk a day for various reasons, including a higher incidence of lactose intolerance in the elderly," she tells WebMD.
"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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