‘Weak link’ between childhood lead and adult criminal behavior

30 December 2017: Lead exposure during childhood has been tied to a variety of developmental problems, but a new study suggests it may not be associated with higher odds of criminal behavior later in life.

The study set out to address a flaw in much of the previous research linking lead and crime: mainly that it’s hard to determine how much of this connection might be explained by poverty and other socioeconomic circumstances that can influence both criminal activity and lead exposure.

Researchers followed 553 people born in Dunedin, New Zealand, in 1972 and 1973, when lead exposure was common among children of all economic backgrounds because of widespread use of leaded gasoline. All of the kids were tested for lead exposure when they were 11 years old, and the study team followed them until age 38 to see how many of them were convicted of crimes.

By the end of the study, 154 participants, or 28 percent, had at least one criminal conviction, the researchers report in JAMA Pediatrics. But the odds of this happening were barely influenced by the amount of lead exposure people had during childhood. Just being male had a stronger effect than lead levels, the researchers note.

“Many studies have shown that higher exposure to lead could predict more criminal behavior, but our study actually found that there isn’t a clear connection between the two,” said lead author Amber Beckley, a researcher at Duke University in Durham, North Carolina.

The reason for the different results this time is that the current study found children from all walks of life had high lead levels, Beckley said by email.

“In our study, socioeconomic status was not associated with childhood lead exposure,” she added.

There’s no safe level of lead exposure. This toxin can damage the developing nervous system in young children, and blood lead levels as low as 5 micrograms per deciliter may lower intelligence quotient (IQ), according to the World Health Organization.

Participants in the current study had average blood lead levels more than twice that high when they were 11 years old in the early 1980s: 11.01 micrograms/dL.

Blood lead levels ranged from 4 to 31 micrograms/dL and didn’t vary according to socioeconomic status.

To see how many of these kids were later convicted of crimes, researchers searched police records and also interviewed participants six times to inquire about any criminal activity.

A total of 68 participants, or 12 percent, had a single criminal conviction and another 86 people had more than one conviction, the study found.

Only 53 people were violent offenders, while 101 participants were convicted of non-violent crimes.

Childhood lead exposure didn’t appear to influence at all whether people would commit violent crimes or become repeat offenders.

But it did appear to influence the odds that teens would participate in criminal activity, though this connection was weak and didn’t persist over time, the authors conclude.

One limitation of the study is that children only got one blood test for lead exposure, and multiple assessments can give a more accurate picture of total exposure, the researchers note. It’s also possible that results would be different today, when children typically have less exposure to lead than they did in the 1970s and 1980s.

It’s also possible that the connection between childhood lead exposure and criminal behavior might be stronger than the authors concluded, David Farrington of Cambridge University writes in an accompanying editorial. It may not be appropriate to describe the strength of the connection as “weak,” Farrington writes.

“More research is needed, of course, to investigate the independent, interactive and sequential effects of blood lead levels in relation to other risk factors for offending,” Farrington writes. He didn’t respond to emails seeking comment.