Vitamin D is so critical to our health that nature designed a fail-safe way to obtain it: from the sun. Throughout history, exposure to the sun gave humans the vital doses needed to build bones, protecting children against the characteristic bowed legs of rickets and adults from osteomalacia, or softening of the bones.
Certainly, some of our vitamin D is provided by foods—fatty fish and egg yolks, for example. But until 1931, when milk began to be fortified with this fat-soluble vitamin, the sun was our main source, its ultraviolet B rays penetrating the skin’s uppermost layer, causing skin cells to produce a vitamin D precursor. (The precursor, along with vitamin D from food, is processed by the liver and kidneys and converted to D3—the active form of the vitamin.)
Now, we spend more time indoors, in cars or behind computers. We drink less milk and when we do go out, slather on sunscreen. It is no coincidence, experts say, that rickets (which had been virtually wiped out until the 1990s) is making a comeback. Scattered cases of rickets in African-American infants and breast-fed babies have been documented as far south as Georgia; just last February, researchers at the University of Pittsburgh found that over 80 percent of pregnant black women and nearly half of pregnant white women (and the babies they later gave birth to) were classified as “insufficient” or “deficient” in vitamin D. Older people in hospitals and nursing homes are especially likely to lack the vitamin; in one study, 57 percent of elderly patients admitted to a Boston hospital were found to be vitamin D-deficient, according to blood samples and diet records. What’s more, dietary surveys suggest that most Americans, young and old, aren’t getting recommended amounts of the vitamin.
Ironically, these deficiencies have been coming to light at the same time research is uncovering promising new roles for vitamin D—much of it suggesting that higher (often much higher) daily doses of the vitamin are needed for optimal health. Researchers have long been urging policy makers to rethink current dietary recommendations, and in recent months their voices have been getting louder. Here, some light on the debate about vitamin D—and what you can do now to stay healthy.
Next: The Promise of D »
The Promise of D
Vitamin D is essential for helping bones absorb calcium, keeping them strong and preventing osteoporosis. Vitamin D also helps maintain muscle strength and balance and lowers the risk of bone fractures in older people. But it seems meant to do more: there are receptors for vitamin D in almost every cell in the body, and evidence is growing that the vitamin helps the immune system function and regulates cell growth.
One clue is the success of vitamin D in treating psoriasis: topical applications of the vitamin help suppress the proliferation of skin cells, reducing the size of the disease’s lesions. Likewise, vitamin D may help quell the uncontrolled growth of cancer cells.
Exciting new research suggests that vitamin D may offer protection against some types of cancer, including breast and prostate cancers and, in particular, colorectal cancer. How vitamin D fights cancer isn’t known for sure, but it “helps reduce cell proliferation and differentiation, and it may reduce inflammation,” says Edward Giovannucci, M.D., professor of nutrition and epidemiology at the Harvard School of Public Health in Boston. Giovannucci, whose work has reported increased risks of digestive system cancers among people with low vitamin D levels, threw down the gauntlet in a keynote speech at the American Association of Cancer Research in 2004. “I would challenge anyone to find an area or nutrient or any factor,” he said, “that has such consistent anti-cancer benefits as vitamin D.”
Research is also revealing vitamin D’s promise in autoimmune disease. For example, a sufficient level of vitamin D may confer some protection against developing multiple sclerosis (MS), a neurologic disease affecting over 2 million people worldwide. Last year, in a study based on blood samples from more than 7 million military personnel, researchers from the Harvard School of Public Health found that those with the highest blood levels of the vitamin were 62 percent less likely to develop MS than those with the lowest vitamin D levels.
Diabetes is also considered an autoimmune disease, since it involves immune-cell attack on the insulin-secreting cells of the pancreas—and vitamin D may have a protective role. In a landmark study from Finland, researchers found that children who were given high-dose vitamin D supplements in their first year of life were nearly 80 percent less likely to have developed diabetes 30 years later when compared with a similar group that did not receive supplements.
Experts are not sure about how vitamin D protects against autoimmune diseases, but believe that it may serve as a brake on the overactive immune cells. “Vitamin D may decrease the development of type 1 T-helper cells,” explains Charles Stephensen, Ph.D., a research scientist at the USDA’s Western Human Nutrition Research Center at the University of California, Davis. These cells are involved in protective immune responses, “but they may also initiate autoimmune disease, especially in people who may have a genetic predisposition.”
Other, preliminary research hints at a connection between inadequate prenatal vitamin D and asthma in young children. Recent data even suggest that low vitamin D may be linked with epidemic influenza (which tends to strike, after all, during sun-deprived winter months).
Next: Vitamin D in Foods »
Vitamin D in Foods
NATURAL SOURCES IU*
Salmon, 3 1/2 oz. cooked 360
Sardines, 1 3/4 oz., in oil (drained) 250
Tuna, 3 oz., in oil (drained) 200
Egg yolk, large 20
Liver, beef, 3 1/2 oz. cooked 15
FORTIFIED FOODS** IU
Milk (cow’s, all % fat), 8 oz. 100
Orange juice, 8 oz. 100
Margarine, 1 Tbsp. 60
Cereals, fortified with 10% DV
(serving size 3/4-1 cup) 40
Source: NIH Clinical Center, Office of Dietary Supplements
**Only fluid milk is routinely fortified; for other foods, read labels to select fortified options.
Next: How Much is Enough? »
How Much is Enough?
For now the U.S. recommendations for adequate intake of vitamin D are 200 international units (IU) per day for adults under age 50, 400 IU for adults aged 50 to 70 and 600 IU for adults over 70.
“How much you need from your diet is inversely proportional to what you make from the sun,” explains Giovannucci. “Lifeguards probably don’t need any from their diet.” But the rest of us need to be more vigilant, unless we take supplements or love drinking milk.
Since many Americans have trouble getting even the recommended doses, the 2005 Dietary Guidelines for Americans—the government’s authoritative voice on what to eat to stay healthy—declared that the elderly, people with darker skin and those exposed to insufficient sunlight (people who are housebound) need 1,000 IU daily—an amount that’s hard to achieve without taking a daily supplement.
What’s more, those recommendations are focused only on keeping rickets and osteomalacia at bay, says Robert Heaney, M.D., a leading vitamin D expert at Creighton University in Omaha, Nebraska: “They don’t in any sense ensure the health of the total body.”
Next: Food First? »
To stay on track, say experts, it makes sense to boost your D wherever you can get it. While it’s usually best to choose foods rather than supplements to supply a desired nutrient, you don’t have many options with vitamin D. Perhaps because nature knew there would always be a backup source in sunlight, few foods naturally contain the vitamin: fatty fish, egg yolks and liver are good sources, but not exactly staples.
Fortified foods can help you close the gap. Among them, milk is the best known; through voluntary but nearly universal fortification, each 8-ounce glass provides 100 IU of vitamin D. That’s helpful, but few of us drink the two to six daily glasses it would take to meet even the minimal recommended intake. Be aware, too, that only milk is routinely fortified—not products made from milk, like cheese, ice cream or yogurt. However, some yogurt manufacturers are now opting to fortify, as are some brands of orange juice, breakfast cereals and margarines. Read labels and try to get a few servings of fortified foods each day, and expect a wider range of choices in the future, says Heaney. “I’d like to get as much vitamin D in the food chain as the regulators will accept.”
Next: A Little Sun »
A Little Sun
Most experts agree that a moderate amount of sun exposure will help boost vitamin D levels without significantly upping skin-cancer risk. But determining a safe amount is highly personal, and tricky. “There’s no one-size-fits-all recommendation,” says J. Leonard Lichtenfeld, M.D., an oncologist and internist who serves as deputy chief medical officer of the American Cancer Society.
Consider geography, season and weather: if you live in regions north of the midsection of the country, sunlight is too weak throughout fall and winter for you to produce enough vitamin D—and clouds or smog could change the equation any time of year. How old you are is important, as skin becomes less efficient at synthesizing vitamin D as you age; a 70-year-old’s skin produces only one-quarter of the vitamin D that a 20-year-old’s does. If you have dark skin, you’ll produce less of the vitamin, since melanin pigments in skin block the UV rays that start the whole process. When compared to a fair-skinned person, someone with darker skin “may require two to three times the amount of time to make the same amount of vitamin D,” notes Giovannucci.
While there’s no official consensus, a good rule of thumb for a safe vitamin D boost is to aim for 5 to 15 minutes of sun, a few days a week, depending on how sensitive you are to the sun. “No one is advocating burning,” says Heaney.
Next: Take a Supplement »
Take a Supplement
Given all these uncertainties, it’s no surprise that all the experts interviewed for this article believe in taking vitamin D daily. Lichtenfeld takes a multivitamin, but the others consider that just a starting point. Giovannucci, who lives in Boston, aims for 1,500 IU daily, but thinks that 1,000 to 2,000 IU might be appropriate for “those with very little sun exposure.” In Omaha, Heaney takes a once-weekly 10,000 IU pill, but suggests 1,000 IU as a good daily goal for all adults. “It won’t be enough for some, it will be enough for many, and everybody will get some benefit.”
Whatever you choose, avoid the D2 form of the vitamin, sometimes called “ergocalciferol.” Though widely used in fortification and supplements, it’s much less potent than the vitamin D3 form. Look for the terms “vitamin D3” or “cholecalciferol” on labels. And don’t opt for cod liver oil as your source, says Heaney. Though it’s loaded with vitamin D, it’s also rich in vitamin A, which most Americans don’t lack: “You could run the risk of toxicity.”
A Sunnier Future
Modern life may have made it harder to get the vitamin D we need daily, but luckily the solutions are simple and close at hand. A couple of servings of fatty fish weekly, a few glasses of milk and an occasional egg yolk—plus fortified foods, supplements and perhaps a little sunshine. It doesn’t sound like a complicated prescription, but it can go a long way toward sending old-time diseases like rickets and osteomalacia back into ancient history where they belong. And, just maybe, it can help ward off modern-day scourges like cancer and diabetes in the future.