The first study to follow lead-exposed children from before birth into adulthood has shown that even relatively low levels of lead permanently damage the brain and are linked to higher numbers of arrests, particularly for violent crime.
Earlier studies linking lead to such problems used indirect measures of both lead and criminality, and critics have argued that socioeconomic and other factors may be responsible for the observed effects.
But by measuring blood levels of lead before birth and during the first seven years of life, then correlating the levels with arrest records and brain size, Cincinnati researchers have produced the strongest evidence yet that lead plays a major role in crime.
The researchers also found that lead exposure is a continuing problem despite the efforts of the federal government and cities to minimize exposure.
The average lead levels in the study "unfortunately are still seen in many thousands of children throughout the United States," said Philip J. Landrigan, director of the Center for Children's Health and the Environment at the Mount Sinai School of Medicine in New York.
The link between criminal behavior and lead exposure was found among even the least-contaminated children in the study, who were exposed to amounts of lead similar to what the average U.S. child is exposed to today, said Landrigan, who was not involved in the study.
"People will sometimes say, 'This is in the past. We are cleaning up lead. We don't have lead problems anymore,' " said criminologist Deborah W. Denno of Fordham University in New York, who also was not involved in the study. "The Ohio study says this is still a big problem."
Nationwide, about 310,000 children between the ages of 1 and 5 have blood lead levels above the federal guideline of 10 micrograms per deciliter, and experts suspect that many times that number have lower levels that are still dangerous.
"It is a national disgrace that so many children continue to be exposed at levels known to be neurotoxic," said neurologist David C. Bellinger of Harvard Medical School, who wrote an editorial accompanying the study published in the online journal PLoS Medicine.
Although some urban soil is still contaminated with lead from gasoline, 80% of lead exposure now comes from houses built before 1978. Paint in such houses can contain as much as 50% lead, and even if it has been covered by newer, lead-free paint, it still flakes or rubs off.
