Boys with relatively elevated levels of lead in their blood may start puberty later than their peers with less lead exposure, a new study suggests.
The findings, published in the journal Pediatrics, add to concerns about the potential health effects of even moderately elevated lead levels.
Lead is a toxic metal that is present in the air, soil and water, though public health efforts in recent decades to reduce environmental levels -- by taking lead out of gasoline and paints, for example -- have cut lead exposure in the U.S. and other countries.
It has long been recognized that children are especially susceptible to the toxic effects of lead, showing cognitive effects such as learning disabilities and a drop in IQ if their blood lead levels climb above 10 micrograms per deciliter (mcg/dL) -- the figure that the U.S. Centers for Disease Control and Prevention (CDC) currently considers the "level of concern."
But a number of recent studies have linked blood lead levels well below 10 mcg/dL to milder effects on children's intelligence and growth.
In the new study, which followed more than 400 Russian boys for three years, researchers found that those with blood lead levels of 5 mcg/dL or higher began puberty an average of six to eight months later than their peers with lower lead levels.
For any one boy, such a difference may not be significant. The study focused on the potential effects of lead on the age of puberty onset -- and not on the risk of a "clinical delay" in puberty.
"For an individual boy, the difference between starting puberty at age 10.5 or 11 might not have any health implications at all," explained lead researcher Dr. Paige L. Williams, of the Harvard School of Public Health in Boston.
However, she told Reuters Health, on the population level, a shift in the average age of puberty onset would push more boys past the age that would typically be defined as "clinical delay" -- about age 13 or later.
Other research has suggested that boys with a clinical delay in puberty face higher risks of low self-esteem, depression and eating disorders compared with their peers.
Williams and her colleagues based their findings on 489 boys who were 8 to 9 years old at the outset. The researchers measured the boys' blood lead levels, and then followed them over time to chart the age at which they began puberty. At the outset, 28 percent of the boys had lead levels of 5 mcg/dL or higher.
By the age of 12, 90 percent of the boys had at least one sign of the beginnings of puberty. But at any given age, boys with elevated lead levels were less likely to have begun puberty.
The findings do not prove that lead directly affected the boy's onset of puberty. However, Williams pointed out, the link held up even after the researchers factored in a number of other variables that might help account for the relationship -- like parents' income and education levels, and the boys' typical calorie and dietary fat intake.
And while lead can affect children's growth, the boys' height and weight did not explain the association between higher lead levels and later puberty.
Williams said there is research in rodents showing that lead can lower levels of testosterone and other hormones, and affect the timing of puberty. And previous studies of girls have found an association between higher lead levels and later puberty.
Together with past research on the possible cognitive effects of relatively lower blood lead levels, these recent findings on puberty onset suggest that the CDC should take a look at its current policy, according to Williams and her colleagues.
"Our study adds to accumulating evidence that suggests they may want to consider setting a lower level of concern," Williams said.
And while this study focused on Russian boys, the findings are probably broadly relevant, according to senior researcher Dr. Russ Hauser, also of Harvard.
Even though this is a Russian population, "it's unlikely that they would respond to lead differently," he said. "We do think it's generalizable to the U.S. population."
Williams said that the average blood lead level for U.S. children is now around 2 mcg/dL, but an estimated 7 to 8 percent have levels above 5 mcg/dL. And that figure is higher among certain children, including minorities and those from low-income families, as well as those living in homes built before 1950, which are more likely to contain lead-based paint.
The study was funded by the U.S. Environmental Protection Agency and the National Institute of Environmental Health Sciences.
SOURCE: Pediatrics, May 2010.
(- Reuters, April 2010)