Low Levels of Lead Damage Children

It can reduce IQ, delay puberty

WEDNESDAY, April 16, 2003 (HealthDayNews) -- Two studies offer more worrisome news about the harm done to children by lead exposure.

One study says IQs are lowered significantly by levels of lead in the blood below those now regarded as acceptable by U.S. health officials.

The other finds delayed puberty in girls with elevated levels of the metal in their blood.

The first study, of 172 children in the Rochester, N.Y., area, found lower IQs in those with blood lead levels of 10 micrograms per deciliter, which the U.S. Centers for Disease Control and Prevention (CDC) lists as acceptable.

Previous studies had found an IQ reduction of seven points for a blood level of 10 micrograms, with IQ declining by another two to three points as levels rose to 30 micrograms.

The new study determined the greatest damage is done as blood levels increase from 1 microgram to 10 micrograms, indicating that levels now regarded as safe are, in fact, damaging.

The study, published in the April 17 issue of The New England Journal of Medicine, was done by a team led by Richard Canfield, director of the cognitive development and neurotoxicology laboratory at Cornell University.

"We were very surprised because it is counterintuitive to think that the amount of damage done to mental function per increment in blood level is greater at lower levels than at higher levels," he says.

There was another surprise: "We obtained these findings when we tested children at the age of 3," Canfield says. "It is counterintuitive to find damage at so young an age."

The study suggests current estimates of a safe lead level may have to be revised, Canfield says: "Our research does not allow you to set a safe level."

But, he adds, more research into acceptable blood lead levels in children is needed. "It is necessary to replicate these findings in other samples," Canfield says. "We need more children at more than one testing site around the country."

The children were first tested at 6 months of age, with additional tests at one year, 18 months, and then yearly up to age 5. The relationship between blood lead levels and intelligence held true up to age 5, Canfield says.

Using the CDC numbers as a gauge, he makes a "very approximate" estimate that 1 million to 2 million children in the United States have lead blood levels in the 5 microgram to 10 microgram range. The CDC says one in 10 children has a blood lead level of 10 micrograms or higher.

The puberty study, which also appears in this week's issue of The New England Journal of Medicine, was done by a group headed by Sherry G. Selevan, an epidemiologist at the U.S. Environmental Protection Agency. It draws on data from 2,500 of the 40,000 girls studied for the third National Health and Nutrition Survey (NHANES), conducted from 1988 to 1994.

"Significant delays in breast and pubic hair development" were found in black and Hispanic girls with blood levels as low as 3 micrograms, the study says. Breast development was delayed anywhere from to two to five months, while pubic hair development was delayed from two to six months.

There were "non-significant" delays in white girls with the same lead blood levels. But this failure to find a cause-and-effect relationship may be due to the relatively small number of white girls in the study, Selevan says.

It isn't possible to say whether the delay is harmful, Selevan says. "You're talking about a basic developmental alteration, and you don't yet know how it will play out in the long run."

The EPA team is now looking at NHANES data for boys to see if the same effect occurs in them. Results might be available "in a year or so," Selevan says.

There is some good news behind this bad news about lead's effect on childhood development, says James H. Ware, dean for academic affairs at the Harvard School of Public Health and co-author of an accompanying editorial in the journal.

"It wasn't so long ago when the mean blood level in this country was high," he writes. "It's now below 3. We were burning leaded gasoline and using leaded paint. This is arguably one of the most successful things the EPA has done. Exposure to lead keeps falling."

The main exposure to lead now occurs in housing built before 1950, where paints with high levels of lead are more common, Canfield says. Lead particles can fall on the floor and be picked up by children, and toys can be contaminated.

More information

Learn about the damage done by lead and ways to prevent it from the National Safety Council or the Philadelphia Department of Public Health.

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