Childhood Vitamin D—A Dark Side?

This is part one of a two-part series. Part II: “Childhood Vitamin D—A New Benefit?” is available at Childhood Vitamin D—A New Benefit?.

Most people don’t get nearly enough vitamin D, best known as the sunshine vitamin. This shortfall can be bad because the vitamin is known to fight cancer, diabetes, osteoporosis, muscle weakness, gum disease, and infections. Sadly, for some urban children there can be a downside to vitamin D: It enhances their bodies’ uptakes of the toxic heavy metal lead.

A research team led by John D. Bogden of the University of Medicine and Dentistry of New Jersey–New Jersey Medical School in Newark has now quantified the effect. In the April Environmental Health Perspectives, Bogden and his team report that among urban African-American youngsters, blood concentrations of lead can rise to potentially toxic concentrations in summer, when their vitamin D concentrations also rise, presumably due to regular sun exposure.

The researchers recruited 142 children who were 8 and under: 91 African-Americans, 51 Hispanics. All came from families participating in the federal Women, Infants, and Children (WIC) program, which provides supplemental food, counseling, and medical screening to low-income women with children.

“What was surprising to me,” Bogden says, “was just how strikingly different blood-lead values were in the African-American and Hispanic kids”—especially since they came from the same city and have similar socioeconomic backgrounds. Lead was virtually undetectable in Hispanic children 4 and older year-round. It averaged about 4 micrograms per deciliter (µg/dl) of blood in the younger kids, but only during the summer. The rest of the year, the youngest children’s blood was virtually leadfree.

However, blood tests from the black children told a different story. In winter, lead averaged about 12 µg/dl of blood in children 3 and under, and roughly 5 µg/dl in the older kids. Come summer, values in both groups spiked dramatically: to about 22 µg/dl in the younger group and 9 µg/dl in the older children. The Centers for Disease Control and Prevention considers blood-lead values of 10 µg/dl and higher as excessive.

Values not benign

Bruce P. Lanphear of Children’s Hospital Medical Center in Cincinnati and his colleagues have shown that in kindergarteners, IQ can fall as blood-lead values climb above 5 µg/dl (SN: 5/5/01, p. 277: Available to subscribers at Even low lead in kids has a high IQ cost). In one study, his team kept track of babies until they reached age 5, and the researchers found that “IQ declined by 7.4 points as lifetime average blood-lead concentrations increased from 1 to10 µg/dl.”

Such findings, Lanphear says, indicate that no concentration of lead is safe.

In the latest study, Bogden found that the most important factors associated with high summertime blood-lead concentrations in black children were the kids’ ages and blood concentrations of vitamin D. Toddlers, who were at highest risk, also get the most dietary vitamin D because they drink a lot of milk fortified with the vitamin. Moreover, children at this age can consume lead-laden dust by putting their hands, toys, and almost everything else in their mouths, says Bogden.

The intriguing question this study raises, he says, is why the Hispanic children’s lead values were so much lower than the blacks’. It’s something his team plans to begin investigating immediately. If the researchers can pin down how Hispanic children generally avoid lead, applying the lesson to blacks “might almost eliminate the problem,” says Bogden. The disparity could trace to different housekeeping practices, he says, or diets.

In fact, he notes, because the body responds to lead much as it does to calcium, “increasing dietary calcium will reduce lead absorption.”

The one solution Bogden doesn’t want to advocate is reducing vitamin D intake. Overall, blacks already have the lowest average blood concentrations of vitamin D of any group in the United States. A major factor in that statistic is that skin pigments filter out much of the vitamin D–making sunshine (see Understanding Vitamin D Deficiency).

Part II: “Childhood Vitamin D—A New Benefit?” is available at Childhood Vitamin D—A New Benefit?.

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Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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