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.