Every few days, it seems, a news report appears, touting another potential payoff of vitamin D. Improves bone and muscle strength! Reduces blood pressure! Wards off colds and flu! Protects you from cancer! The hype is enough to make you wonder if this vitamin also files taxes and cleans closets. So if you’re a little skeptical, join the club—and check out the surprising report that appeared last May in the Journal of the American Medical Association. The study found that women 70 and older who took a single annual superhigh dose of D actually had a higher rate of bone fractures than those who received a placebo—a result that appeared to shoot holes in the well-accepted link between D and bone health and left even D-votees scratching their heads.

Vitamin D experts were quick to spot chinks in the JAMA study. “The finding could have been connected to the single high dose—500,000 IU. Most people take much less, 1,000 to 2,000 IU daily,” says Anthony Norman, PhD, a vitamin D expert and professor of biochemistry and biomedical sciences at the University of California, Riverside. (The official recommendation is 200 IU for women 19 to 50 and 400 for those 51 and older, but the Institute of Medicine is likely to suggest upping it to 1,000 IU.) “One study doesn’t change our whole thinking about D,” Norman adds. Still, after witnessing the rise and fall of so many fashionable supplements over the years (remember vitamin E? ginkgo biloba? beta carotene?), you have to wonder: Is D really any different?

“I think D has earned the attention it’s getting, because having low blood levels of the vitamin is associated with a variety of diseases,” answers Walter Willett, MD, chair of the department of nutrition at the Harvard School of Public Health. Since about half of all women have a D deficiency, many of us could be unwittingly putting ourselves at increased risk of everything from colds to cancer. So far, scientists have found vitamin D receptors in 37 types of tissue, from bone to breast to cartilage. “Given the potentially widespread effects of a deficiency, it makes sense to try to maintain a healthy level of the vitamin,” Norman says.
 First Step: Get a Read on Your D
“Women in midlife should have a blood test to find out if they’re low on D,” says Kathy McManus, RD, director of nutrition at Brigham and Women’s Hospital in Boston. “Despite the JAMA study, we know that D is important for bone health because it improves calcium absorption, and that becomes increasingly critical as you go through menopause. To help prevent the fractures half of women 50 and older experience, you need to make your bones as strong as possible.” The most widely used measurement assesses your blood level of 25-hydroxyvitamin D in nanograms per milliliter. A score of 30 to 80 nanograms is considered sufficient.
 The Challenges of Getting Enough D
If you’re low, you should bring your level into the normal range, but that’s not as simple as it sounds. “D isn’t found in most natural foods—which means it’s difficult to get from diet alone,” says Marion Nestle, MPH, PhD, a professor in the department of nutrition, food studies and public health at New York University and the author of What to Eat. Fruits and vegetables contain no D, and meat has little. Fatty fish like wild sockeye salmon has one of the highest levels—about 794 IU per three-ounce serving—but farmed fish has much less. Even fortified foods like milk, breakfast cereal and orange juice contain fairly negligible amounts. A cup of milk, for instance, has just 115 IU.

Since D is also produced when ultraviolet B rays strike the skin, the easiest way to get enough is to expose unprotected skin to the sun for 10 to 15 minutes between 10 am and 3 pm a day. But this strategy works only if you live in a sunny climate—and are willing to gamble on upping your odds of getting skin cancer. “Sun exposure causes cumulative damage to the skin, so this is probably not the best way to get D,” says Melvin Chiu, MD, a dermatologist at the David Geffen School of Medicine at the University of California, Los Angeles.

Can you wear sun block and still get vitamin D from solar rays? According to conventional wisdom, sunscreen blocks all D production, but a recent review by Chiu and a colleague suggests it’s not that simple. “Most people don’t apply enough or reapply if they’re spending a lot of time in the sun,” he says. Even so, if you’re a regular sunscreen user (and you should be), you can’t count on producing enough D to maintain healthy levels. Enter the supplements.

How much to take? Most experts agree that 1,000 to 2,000 IU per day is safe, but the bottom end of that range probably isn’t enough to boost those who are low on D into the adequate level. “Only half of people who have insufficient amounts of D will get to 30 nanograms per milliliter by taking a dose of 1,200 IU a day,” Norman says. To be cautious, start with a 1,000-IU dose and see where you are in two months; if you’re still low, bump it up to 2,000. “Two thousand should bring most people into the desirable range,” Willett says.

Look for a D3 supplement, which provides the kind of D created when skin is exposed to the sun. It raises blood levels more effectively than D2, the plant-based form. You can improve vitamin absorption by as much as 50 percent if you down your pill with your biggest meal of the day, a Cleveland Clinic study reports. “Most people take D with orange juice or toast in the morning, but it doesn’t seem to be well absorbed unless you also eat some fat, because D is fat soluble,” says Angelo Licata, MD, an endocrinologist who worked on the study.

Don’t expect the so-called sunshine vitamin to leave the spotlight anytime soon. “This is probably the hottest topic in nutrition research,” Willett says. “Stay tuned for further details.”

Originally published in the September 2010 issue of More.