Vitamin D has been credited with helping to fight everything from colds to cancer. But many of us aren't getting enough. We'll help you get an A when it comes to D.
baby bottle of milk
Credit: Lucas Zarebinski

Three years ago, when Erin Danner kept complaining that her right leg and foot hurt, her parents, Jacqueline Danner and Omar Danner, M.D., were concerned. A high-energy 5-year-old from Atlanta, Erin loved ballet and played around the house like any kid, says her dad, assistant professor of surgery in trauma and critical care at Morehouse School of Medicine. Her pediatrician found nothing amiss but ordered an X-ray to be safe.

"The scan looked normal," remembers Dr. Danner. The verdict: growing pains. But when Erin's aches persisted and another X-ray was negative, the Danners took her to an orthopedic specialist. He ruled out juvenile rheumatoid arthritis.

Finally, last December, Dr. Danner asked the pediatrician to test Erin's vitamin D levels. Knowing that D deficiency is widespread, especially in African Americans, as the Danners are, he wondered if that might be the culprit. Sure enough, Erin's D levels were well below normal. She was diagnosed with osteopenia, a painful softening of the bones caused by a vitamin-D deficiency that is often a precursor to rickets. "I was shocked," says Jacqueline Danner.

Nicknamed "the sunshine vitamin" because the sun activates its production in our skin, D is actually a hormone that helps bones absorb calcium, keeping them healthy and strong at every stage of life. When we don't have enough calcium, our body draws it from our bones in order to keep a normal amount circulating in our blood. This can make bones weak for life, says Catherine M. Gordon, M.D., director of the Bone Health Program at Children's Hospital Boston. However, a recent study in the Journal of Bone and Mineral Research found that to boost bone density in adults, it's even more important to correct low levels of D than to increase calcium intake. "Most of us do not meet the recommended daily allowance for calcium," says Frank R. Greer, M.D., former chair of the American Academy of Pediatrics (AAP) committee on nutrition. "But doctors are far more concerned about D."

However, an explosion of research suggests that D's benefits extend far beyond bone health. Every tissue and cell in our body contains D receptors and studies have linked low D levels to conditions ranging from the common cold to cancer.

We all need at least 30 nanograms per milliliter (ng/mL) of vitamin D in our blood to have what are considered sufficient levels for bone health. Levels between 20 and 29 signal an insufficiency; levels below 20, a deficiency. (Erin's levels, at 20.3, were borderline deficient.) According to an analysis of government data of kids ages 1 to 21, about 7.6 million are D deficient and another 51 million have insufficient levels. At least 10 percent of U.S. adults are D deficient too, according to a recent study in The American Journal of Clinical Nutrition. (Other studies put the number as high as 75 percent.) "We thought vitamin D deficiency was a thing of the past," says Deepak Kamat, M.D., Ph.D., vice chair of pediatric education at Children's Hospital of Michigan, in Detroit. "We never thought we'd see it in this day and age."

Can of sardines
Credit: Lucas Zarebinski

The D List of Illnesses

Without enough D, babies can develop rickets, which softens bones, leading to bowed legs, knock-knees, and other deformities. But healthy bones aren't the only reason children need D. "Vitamin D activates the body's immune response as well as cells that kill bacteria and viruses," explains Michael F. Holick, M.D., Ph.D., professor of medicine, physiology, and biophysics at Boston University Medical Center, and the author of The Vitamin D Solution. Earlier this year, researchers in Japan reported that schoolchildren taking a daily supplement of 1200 IU of vitamin D reduced their rate of influenza by almost half. Meanwhile, researchers from Finland have reported a strong association between vitamin D supplementation during infancy and a reduction in the risk of type 1 diabetes.

D may also reduce inflammation in various parts of the body, such as the heart and lungs. Inflammation is an underlying cause of cardiovascular disease -- which can begin in the first decades of life. It contributes to the formation of plaque in arteries, making it hard for blood to travel through vessels, raising blood pressure. Vitamin D seems to keep blood vessels flexible and helps the heart beat more efficiently. A 2009 government analysis of more than 3,500 12- to 19-year-olds linked levels below 15 ng/mL to high blood pressure, high blood sugar, and metabolic syndrome, a risk factor for heart disease. Adults with low levels are two to three times more likely to die of heart failure than those whose levels are sufficient, according to a recent Journal of Cardiac Failure study. And too little D may increase the risk of kids' asthma and worsen symptoms. Children with a D insufficiency were 50 percent more likely to have a serious asthma attack, found Harvard researchers. Adults with asthma who also have low D levels have twice the degree of airway constriction than those with higher levels.

Cancer may be D-sensitive too. "Some evidence suggests that when people have inadequate vitamin D, they're at an increased risk for colon cancer," says Cindy D. Davis, Ph.D., program director of the Nutritional Sciences Research Group at the National Cancer Institute.

D deficiency may even affect pregnancy. In preliminary research at the Medical University of South Carolina, in Charleston, pregnant women who reached ideal D levels via supplements experienced fewer complications -- including gestational diabetes and preterm labor -- compared with women who did not take them, says Carol Wagner, M.D., a pediatrician and neonatologist who led the study.

Glass of orange juice
Credit: Lucas Zarebinski

The D Challenge

To achieve sufficient D levels, the Institute of Medicine (IOM) advises that everyone get 200 IU of D per day until age 50. In 2008 the AAP doubled its D recommendations for children from 200 to 400 IU daily, which is the equivalent of a quart of D-fortified milk or formula. (The IOM was expected to increase its recommendations on November 30, after this story went to press.) Since breast milk doesn't contain D -- and babies shouldn't drink cow's milk until age 1 -- the AAP advises that partially or exclusively breastfed infants receive a supplement of 400 IU of liquid D every day. "This is enough to keep your child from being D deficient," says Dr. Greer, who coauthored the academy's statements on D.

More doctors are now testing their patients' vitamin D levels. For the last quarter of 2009, tests surged by more than 50 percent compared with that period in 2008, reports Quest Diagnostics, the nation's largest medical laboratory company. "I'm seeing a lot of kids with chronic fatigue and muscle aches, so I'm checking D levels and often finding very low ones," says pediatrician Kathi J. Kemper, M.D., chair for holistic and integrative medicine at Wake Forest University School of Medicine, in Winston-Salem, North Carolina.

Why do so many of us earn an F when it comes to D? It's simply not found in many food sources, for one thing (see "Where the D Is" on page 7 for options). But being overweight is also a factor. Because D is fat soluble, it gets stored in fat tissue, so less of it remains in the bloodstream. "Most obese adults need two to three times more D than normal-weight people to satisfy their requirement," says Dr. Holick. It's not clear whether this is also the case with children, because studies haven't been done on them.

The Sunscreen Debate

Experts are firmly divided into two camps when it comes to the matter of sunlight and vitamin D. The main reason that most of us are short on D is because we simply aren't outside very often. And when we are, we may wear sunscreen or protective clothing to guard against skin cancer. Plus, the angle of the sun from November through March in northern states prevents us from getting the rays we need. Regardless of where you live, early-morning or late-afternoon sun doesn't help you make D. If you have dark skin, melanin makes it even harder to produce enough.

The obvious solution seems to be to spend time in the midday sun without protection. But this advice, advocated by some vitamin-D experts, has become a lightning rod for controversy. In one corner are people like Dr. Holick. You don't need lots of sun to boost D levels, he says; you can benefit from five to 30 minutes of unprotected exposure two to three times per week, depending on your skin color. If you get plenty of sun during the warmer months, you can make enough D to carry you through the winter, he adds. "I don't put sunscreen on my kids for the first ten minutes they're in the sun," says D researcher Michal L. Melamed, M.D., assistant professor in the departments of medicine and epidemiology at Albert Einstein College of Medicine, in New York City.

In the other corner are those who say that it's best to avoid sun exposure. "Kids should wear sunscreen all the time, and babies under 6 months should stay out of the sun," insists Dr. Greer. Pediatrician Maribeth Bambino Chitkara, M.D., a spokesperson for the Skin Cancer Foundation, agrees. Since her 29-year-old sister died of melanoma, she believes that sun protection can't start too early. "UV light is carcinogenic," she says. "We can't separate the potential benefits of UV-light exposure from the inherent harm associated with that exposure."

Adults also need to take precautions, says New York City dermatologist Doris Day, M.D., another spokesperson for the Skin Cancer Foundation. "Most people get more sun than they realize even if they wear sunscreen. Why take a risk from sun exposure when a supplement will provide the same benefits?"

The Supplement Question

But there is one big difference between the D your body produces in response to sunlight and the kind that comes from a bottle. Sun-activated D lasts twice as long in your body, which is why you only need sun exposure a few days a week, notes Dr. Holick. If you or your child avoid the sun and don't drink enough milk or eat lots of D-rich foods, a daily supplement or a multivitamin can help you meet AAP and IOM guidelines. (The D3 form is more effective at raising blood levels than D2.) Both pregnant and nursing women need a prenatal vitamin containing 400 IU of D per day.

Anyone who's found to have low D levels will be given supplements. Erin Danner's treatment consisted of two over-the-counter D-fortified calcium chews a day -- a total of 1,000 IU of D -- and more milk. Within four months, her levels had risen from 20.3 to 34.8. "Erin was doing cartwheels at summer camp and hasn't complained about pain for months," says her dad. Still, her doctor wants her to continue taking the calcium chews to boost her D levels above 40 and keep them there.

Depending on whom you talk to, vitamin D is either the best thing since sliced bread -- or a story that's still unfolding. The ideal amount is still the great unknown. The government says that the safe upper limit for D is 1,000 IU for babies younger than 1, and 2,000 IU for everyone else, but some experts maintain that higher doses are fine. In fact, the Vitamin D Council, a nonprofit that educates people about D deficiency, advises that everyone over age 1 take 1,000 IU for every 25 pounds they weigh. "With most adults, 5,000 IU per day is adequate to maintain optimal D levels," says John Cannell, M.D., president of the council.

Many experts think it's best to wait for more studies before jumping on the vitamin-D bandwagon. "While it makes sense to keep D levels in the normal range, we need clinical trials before we make public health recommendations that everyone take a D supplement," says Judith Wylie-Rosett, Ed.D., R.D., a spokesperson for the American Heart Association.

Dr. Gordon is among those who are firm believers in its potential. "More studies are coming to the same conclusions about D's promising effects throughout the body. This is very exciting and something we must pay attention to," she says. "But we need more research about D's risks and benefits, especially when it comes to children. Hopefully, that day won't be too far off."

Should You Have Your Family's D Levels Checked?

Experts say that as long as you and your kid regularly consume D and you're not at high risk for a deficiency (you don't have dark skin, for instance) there's no need to know your levels. If you ask your doctor for the test, your health insurer probably won't cover it without a suspected diagnosis. In that case, plan on spending between $40 and $200 or more out of pocket, depending on where you live. You'll likely need the 25 (OH) D test, for 25-hydroxyvitamin D.

Where the D Is

A growing number of foods, especially grains and dairy products, are D-fortified these days. Still, it can be tough to get the 400 IU a day that experts say we all need. The main D sources:


Serving Size

D Content (IU)

Salmon, cooked

3.5 oz.


Sardines, canned

1.75 oz.


Shiitake mushrooms

4 mushrooms


Tuna, canned in oil

3 oz.


D-fortified cheese

About 3 oz.


Fortified milk

8 oz.


Fortified soy milk

8 oz.


Fortified orange juice

8 oz.


Lactaid, 1%

8 oz.


Originally published in the December 2010 issue of Parents magazine.

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