The Truth About Vitamin D

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

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."

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