Inadequate Vitamin D Levels Common Among Children

PHILADELPHIA, July 9 -- Half of otherwise healthy children and adolescents in the northeastern United States don't get enough vitamin D, researchers found.

Black youth were particularly at risk for low serum 25-hydroxyvitamin D levels in the cross-sectional study, reported Babette S. Zemel, Ph.D., of The Children's Hospital of Philadelphia, and colleagues in the July issue of the American Journal of Clinical Nutrition.

More than 90% of black children and adolescents had 25-hydroxyvitamin D below 30 ng/mL in winter months and 19% had concentrations below 10 ng/mL, putting them at risk for myopathy and rickets.

Low levels were also associated with older age and low daily dietary vitamin D intake.

However, the researchers noted, recommended 25-hydroxyvitamin D levels were set with adults in mind. "Further studies are needed to determine the serum 25-hydroxyvitamin D concentration that indicates vitamin D adequacy for children," they wrote.

Because the prevalence of inadequate vitamin D has been poorly defined in children, the researchers analyzed serum 25-hydroxyvitamin D data from a cross-sectional study of skeletal development among 638 healthy boys and girls ages six to 21 living in the Philadelphia area.

Only the 382 participants who provided a nonfasting blood sample were included in the analysis. These children and young adults did not differ from those who did not provide a blood sample except that they were older on average.

Their vitamin D intake was assessed with 24-hour recall interviews at the baseline office visit and then twice by telephone over the next three weeks. It averaged 206 IU per day, just above the recommended adequate daily intake of 200 IU.

Participants also underwent whole-body, dual-energy X-ray absorptiometry (DXA) scans to determine fat mass and lean body mass. The researchers generated age-, sex-, and ethnicity-specific z scores based on distribution within the sample.

The majority of participants were white, 37% were black, and 7% were Hispanic. Few were overweight (4.5%) because body mass index above the 95th percentile at screening was an exclusion criterion.

Overall, 55% of the participants had inadequate serum 25-hydroxyvitamin D concentrations, defined as below 30 ng/mL according to adult standards.

Five percent had serum 25-hydroxyvitamin D concentrations below 10 ng/mL, "a concentration associated with clinical myopathy, osteomalacia, and rickets," the investigators noted.

The prevalence of low 25-hydroxyvitamin D levels was even higher -- 68% -- among those tested during the winter (44% of visits occurred from November through March).

Black youth were disproportionately likely to have inadequate wintertime 25-hydroxyvitamin D levels: Almost all (94%) failed to reach 30 ng/mL and 19% had less than 10 ng/mL.

Factors independently associated with low vitamin D status in a multivariate, ordinal, logistic regression analysis were:

• Black race (odds ratio 14.2, 95% confidence interval 8.53 to 23.5, P

Further study is needed to document the benefit of screening for and treating low 25-hydroxyvitamin D levels in healthy children and to prospectively measure their sun exposure and outdoor activities, they said.