BAKERSFIELD, Calif. -- Vitamin D, which kids can get from fortified milk, salmon, and moderate exposure to the sun, is thought to improve bone health and may also help prevent cancer.

In the first nationally-representative study of vitamin D levels in children, researchers from Children's Hospital, Boston analyzed government data between 2001 and 2006 for kids 11 and under.

They found that, under the current standards set by the American Academy of Pediatrics, approximately 6 million U.S. children are vitamin D deficient.

There is controversy, however, as to whether this standard is actually too low.

When using more stringent standards for pediatric vitamin D levels, it is estimated that as many as 24 million children are vitamin D deficient, including 92 percent of non-Hispanic black children, and 80 percent of Hispanic children.

Researchers said that more studies are needed to determine the appropriate vitamin D requirements for children so that parents and pediatricians can better gauge how to supplement their child's diet.