How can I be sure my children are getting enough vitamin D?

This is a great question for your pediatrician the next time you take your children to the doctor. If your health care team has concerns about a vitamin D deficiency, it can take steps to diagnose the problem and offer insight on whether a daily vitamin D supplement is in order.

The problem appears to be more common than previously thought. Two recent studies in the Journal of the American Academy of Pediatrics examined blood levels of vitamin D, using a measure of 30 nanograms per milliliter of blood as "desirable." One study, including children and young adults ages 1 to 21, found that 9 percent had blood levels under 15 nanograms per milliliter, and another 61 percent had levels between 15 and 29 nanograms per milliliter.

The other study looked at adolescents and found an average vitamin D blood level of 24.8 nanograms per milliliter. Adolescents with darker skin tended to have lower levels, with an average of 15.5 in blacks and 21.5 in Mexican Americans, compared to 28 in whites. That is likely because darker skin has more of the pigment melanin, which makes it more difficult for the skin to produce vitamin D when exposed to sunlight.

Some authorities say that fair-skinned people need as little as 15 minutes in the sun each day (without sunscreen) to allow the body to make the vitamin D it needs; people with darker skin may need three to five times that much. But before sending your children into the back yard, it's important to know that the American Academy of Dermatology recommends always using sunscreen -- going without, even for short periods, increases the risk of skin cancer. Talk to your pediatrician about what's best for your children.

The recent studies on vitamin D deficiency also uncovered a sobering finding: Low levels of vitamin D are associated with factors, such as high blood pressure, that could lead to heart disease.

The American Academy of Pediatrics recommended increasing the daily intake for vitamin D for children from 200 International Units (IUs) to 400 IUs. Child-friendly foods containing a substantial amount of vitamin D include milk (100 IUs in each cup); tuna canned in oil (200 IUs in 3 ounces); and fortified cereal (levels vary; check the Nutrition Facts label). On food labels, vitamin D is listed as a percentage; the goal should be to get 100 percent of the Daily Value each day.

Read more about the issue in Ohio State University Extension's "Eat, Save, and Be Healthy" Web blog.