Dearth of Vitamin D Is Common in Kids

Researchers at Children's Hospital of Philadelphia have found that 55 percent of otherwise healthy children and teenagers they tested had inadequate amounts of vitamin D in their blood. In many cases, the lack of D was enough to interfere with calcium absorption and healthy bone development. In addition to building strong bones, vitamin D helps the body's immune system function, and scientists increasingly think that a deficiency of the vitamin can contribute to a number of health problems, including asthma, high blood pressure, cancer, and type 1 diabetes.
While a healthy diet contains sources of vitamin D, including fortified milk and certain kinds of oily fish, the human body largely makes its own when ultraviolet light in sunlight shines on the skin. People's vitamin D blood levels generally drop in winter, when sunlight is weaker, and people are outdoors less. All of the study participants' vitamin D levels ebbed in winter.

In addition, people with dark skin are more apt to be vitamin D deficient than light-skinned people, because the melanin in their skin blocks ultraviolet rays. In the Philadelphia study, which examined kids age 6 and up, more than 90 percent of the black participants were deficient in vitamin D in the winter; 19 percent had levels low enough to cause rickets, a disease in which bones soften and bend. The research was published in the July issue of the American Journal of Clinical Nutrition.

The researchers also found that the older teenagers they tested had less vitamin D in their systems than did those younger than 15. Teenagers tend to drink less milk, which is fortified with vitamin D and is the main dietary source of the vitamin for most people. But the researchers adjusted their data to account for differences in dietary intake, and still found the teenagers to have less vitamin D. Babette Zemel, an author of the study and director of the Nutrition and Growth Laboratory at Children's Hospital of Philadelphia, speculates that children tend to spend less time playing outdoors once they enter their teens. The lack of sun exposure might account for the decline. "Parents should be aware of the importance of getting their kids outside," Zemel says. "If you have children who are sensitive to the sun and likely to sunburn, give them at least a few minutes of sun exposure before putting on sunscreen." Like melanin, sunscreen blocks the ultraviolet rays that prompt the skin to make vitamin D, and well-intentioned parents who slather their children with the lotion and keep them out of the burning rays may inadvertently be contributing to vitamin D deficiency.

Babies are particularly susceptible to vitamin D deficiency, because they're rarely in the sun enough to generate their own supply of the vitamin. In 2003, the American Academy of Pediatrics recommended that all infants take in at least 200 international units of vitamin D daily, starting in the first two months of life. That recommendation was prompted by an increased number of cases of rickets in infants. Babies who are breast-fed are especially at risk of vitamin D deficiency, because breast milk doesn't contain enough to meet that minimum. (Baby formula, however, is fortified with vitamin D.)

The pediatricians' group also recommends that older children and teenagers take in a minimum of 200 IU of vitamin D daily, the equivalent of two 8-ounce glasses of milk, because it's hard to know how much sun exposure a child is getting in the course of everyday life. (The pediatricians don't recommend giving children multivitamin supplements generally, saying that children should get their nutrients by eating a variety of healthy foods.) But Zemel says so little research has been done on the vitamin D needs of healthy children that it's hard to say if that's enough. "We're not sure what the optimum level of vitamin D should be."

source:health.usnews.com