Shedding New Light on Vitamin D

Could a little sun be good for you?

vitamin d research We already know it's important for strong bones, but vitamin D may lengthen your life, too. Recent studies suggest D can boost your immune system and lower your risk of some types of cancer and heart disease. Since sunshine stimulates vitamin D production, is it time to do some old-fashioned sunbathing this summer?

Not so fast, sun worshippers. More than a few minutes of unprotected exposure to the sun's ultraviolet light can still give you sunburns, prematurely age your skin and increase your risk for skin cancer. As for tanning beds, forget it -- they are known to be carcinogens. But the good news is most people only need 10 minutes of summer sun a day to get plenty of vitamin D. Add a few good foods to your diet, or perhaps a supplement, and you're, well, golden.

So before your next beach day, here's what you should know about vitamin D, sunshine, your skin and your health.

NEXT: D is for … Death Defying?

D is for … death defying?

Why are conditions such as colon cancer, multiple sclerosis and type 1 diabetes less common in areas with plentiful sunlight? Some research points to an abundance of vitamin D, the only nutrient our bodies synthesize from sunlight. Vitamin D, it turns out, plays an important role in regulating the immune system.

It may even lengthen your life. In 2007, a study analyzing 18 clinical trials found that people who took vitamin D supplements regularly had a 7 percent lower death rate over five and a half years. "That could translate into one or two more years of life," says Philippe Autier, M.D., of the International Agency for Research on Cancer, one of the study authors. Other conditions that may be deterred by vitamin D:

Cancer. A 2007 controlled study of nearly 1,200 postmenopausal Nebraska women linked supplements of vitamin D and calcium to a 77 percent lower risk of all cancer, but the strongest evidence is for prevention of colon cancer, according to several large-scale studies. Some studies also show possible benefits against breast, prostate and other cancers.
Heart disease. Adequate vitamin D may help control high blood pressure and protect against heart disease, studies show.
Multiple sclerosis (MS). Researchers at Harvard studied blood samples of military personnel and found that white Americans with the highest levels of vitamin D were 62 percent less likely to develop MS, an autoimmune neurological disease, compared to those with the lowest levels. The finding didn't extend to people of other races, though, possibly because of inadequate sample size. Another Harvard study found that women with the highest intake of dietary vitamin D had a 33 percent lower risk for MS, and women with the highest intake from supplements had a 41 percent lower risk, compared to women with the lowest vitamin D intakes from diet or supplements.
Depression. Vitamin D deficiency has been associated with mood disorders in older people, but more research is needed before a clear link can be established. Taking vitamin D supplements has not been proven in studies to relieve symptoms of depression.
Other conditions. There is some preliminary evidence that vitamin D may play a role in preventing some infections, rheumatoid arthritis, diabetes (type 1 and type 2), dementia and macular degeneration, a common eye disease.

NEXT: Getting Enough?

Getting enough?

Few Americans get enough vitamin D. A recent study found that three-quarters of Americans have blood levels of vitamin D below what is thought to be needed for optimal health.

So how much vitamin D do you need? The U.S. government suggests 200 international units (IU) daily for people up to age 50, 400 IU from 51 to 70, and 600 IU over age 70. (The body's ability to process vitamin D declines with age.)

Some scientists believe the recommendations should be increased to 800 IU or even 1,000 IU a day. Government organizations including the U.S. Department of Health and Human Services and Health Canada are studying whether to increase the recommended daily vitamin D requirement. Robert P. Heaney, M.D., of Creighton University in Omaha, NE, an endocrinologist and expert on vitamin D, agrees that the daily recommendation should be increased. He starts his patients with osteoporosis on 1,000 IU daily, and increases that for some patients to as much as 2,000 IU.

It's difficult to get these levels of vitamin D just from eating food. A cup of milk, for example, provides only 100 IU. You can also get some vitamin D in other fortified foods such as certain cereals, juices, yogurt and some soy products. Wild fatty fish are a good source, but levels in farmed fish are often much lower, notes Dr. Heaney.

Then there's the sun. On average, during spring and summer months, you only need to go out in the sun, without sunscreen, for about 15 minutes, a few times a week to reach the current vitamin D recommendations. Most people get 10 or 15 minutes of sun weekly just going to their car and mailbox, according to James Spencer, M.D., a dermatologist in St. Petersburg, FL and a former director of dermatologic surgery at Mount Sinai School of Medicine in New York City.

Dermatologists, who often treat skin cancer, are understandably reluctant to encourage sun exposure. "Individuals who intentionally expose themselves to UV radiation for vitamin D are putting their health at risk for developing skin cancer," says Dr. C. William Hanke, M.D., immediate past president of the American Academy of Dermatology, in a written statement. The Academy recommends applying sunscreen and not sunbathing at all, especially from 10 a.m. to 4 p.m. when the sun's UV rays at the strongest.

The amount of vitamin D you can get from the sun depends on your skin pigment, where you live, time of year, age and other factors. From November through February, for example, people who live above 42 degrees north latitude -- think Boston or Milwaukee -- get minimal amounts of vitamin D from the sun.

NEXT: Need a Supplement?

Need a supplement?

If you live in an area with little sunlight during parts of the year, a vitamin D supplement may be recommended. Others who may have a particular need for vitamin D supplements include:

Dark-skinned people, who synthesize less vitamin D from sunlight than light-skinned people
Children (especially infants who are breastfed exclusively) and adolescents, women who are pregnant or breastfeeding
People who have liver or kidney disease or a disorder that hinders vitamin D absorption, such as Crohn's disease or cystic fibrosis
Those who have undergone gastric bypass or take certain medications, such as corticosteroids

If you are concerned about your vitamin D intake, talk to your doctor. You can find out if you have a deficiency with a simple blood test.

Many multivitamins include vitamin D, and so do many calcium supplements. You may consider taking more than the current recommendation of vitamin D, but be careful about overdoing it. Expert opinions on the benefits and risks of higher intake from supplements are mixed. Studies are underway, but for now the U.S. government warns that consuming more than 2,000 IU a day from supplements and food over a long period can be toxic. Our bodies store vitamin D in the liver and fat, so it can accumulate and be used as needed.

The bottom line? In general, spending a few minutes outside every day during the spring and summer, even when it's cloudy, is unlikely to do harm and may improve your vitamin D intake. After 5 or 10 minutes, make sure to apply sunscreen liberally to exposed skin areas (many people put on too little), and even when you do, don't bake. It's also wise to avoid the sun's strong midday rays. Still, it's nice to know that spending time outside on sunny days, which feels so good, might actually be good for you -- if done in moderation.

View the Slideshow: The Sunshine Vitamin