Needleman,
NL, C McFarland, RB Ness, SE Fienberg and MJ Tobin. 2003. Bone
lead levels in adjudicated delinquents. A case control study.
Neurotoxicology
and Teratology 24:711-717
This
study tightens the scientific links between lead exposure and
delinquency in teenagers, finding a strong association
between elevated bone lead concentrations and the risk of being arrested
for criminal behavior.
The
underlying causes for this association are not certain. One possibility
is that lead interferes with impulse control and that people who have
a harder time controlling impulses are more likely to engage in criminal
behavior. Another possibility arises from lead's well-established impact
on cognitive function and classroom performance. Teenagers with higher
lead levels are more likely to fail in school and drop out. Drop-outs,
on average, are more prone to committing crimes.
Both
causes could be operating at the same time.
Importantly,
Needleman et al. are not asserting that all delinquency is due
to lead poisoning. Rather, their results indicate that the loss of impulse
control (or increased dropout rate) caused by lead poisoning create circumstances
where lead-poisoned teenagers are more likely than they would have been
to commit serious criminal offenses.
The
good news here is lead poisoning can be prevented, pointing toward
an important new opportunity for primary prevention of delinquency.
What
did they do? Needleman et al. measured lead levels in
the bones of 194 males who had been arrested, found by the Juvenile Court
of Allegheny County to be delinquent and assigned to one of two programs
within the county for serious delinquents. Both programs serve as alternatives
to jail or to provide care after jail. Many of the juveniles in these
programs are serious offenders, classified by the court as drug dealers,
auto thieves, robbers, etc.
They
then compared these lead levels with 142 controls chosed from 6 of Pittsburgh's
11 high schools. Controls were evaluated using a questionnaire designed
to eliminate "true delinquents" from the control group who engaged
in behaviors similar to the delinquents but somehow simply not been arrested.
Needleman
et al. go to great length to control for confounding variables
such as race, number of parents in the household, parental education,
parental occupation, number of children in the home and neighborhood crime
rate.
What
did they find? Overall, delinquents had significantly higher
lead levels than controls: 11 vs 1.5 ppm. This finding was highly significant
(p=0.007). For all subjects, after adjusting for a range of potentially
confounding variables, the odds ratio was 3.7 (95% confidence interval
1.4 to 11.1).
Importantly,
while race and the number of parents in the home were important factors
in predicting delinquency, Needleman et al. showed convincingly
that the effect of lead was independent of these two variables.
In
addition to analyses with data from both races pooled, Needleman et
al. also performed analyses on white and black delinquents separately,
comparing them, respectively, to white and black controls. The same pattern
held: delinquents had higher lead levels. The odds ratios for white delinquents
compared to white controls was 3.8 (1.1 - 13.1), while for black delinquents
vs black controls it was 2.2.(0.5 - 10.0).
White
delinquents had higher bone lead levels than African American delinquents:
20 vs 9 ppm.
White
delinquents were more likely to come from single-parent homes than white
controls.
What
does it mean? As Needleman et al. comment, "most
studies of the causes of criminal behavior have focused on social risk
factors; less attention has been given to the influence of brain dysfunction."
Their results shine a spotlight on this alternative influence, revealing
that an acknowledged developmental neurotoxicant, lead, is found at significantly
elevated levels in the bones of juvenile delinquents compared to controls.
What
might drive this association? Needleman et al. review a series
of studies demonstrating that lead-exposed children are more likely to
be impulsive and to have attention problems. The detail mechanism by which
lead exerts this influence is not known, but lead's ability to affect
a large number of sites in the central nervous system (CNS) is well-established,
including brain centers that affect impulse control. These effects are
developmental: exposure in the womb and in early childhood disrupts proper
brain development, in ways that can be permanent.
How
important is this observation? Citing prior work by T.E.
Moffitt, Needleman et al. observe:
| |
Abnormal
CNS function is frequently found in the most serious delinquents.
Those delinquents who display anti-social behavior early in life persist
in their behavior, while those who start later tend to give it up
in their late teens. Those offenders in the group of life-persistent
delinquents have a higher rate of impaired neuropsychological function
when compared to those begin later. This early onset/life
persistent group, approximately 6% of the population, is responsible
for 50% of the crime. |
|
One
of the details of Needleman et al.'s results warrants further
comment. They found that the effect of lead was stronger in white delinquents
than in black. According to Needleman et al.: "This apparent paradox
occurs because non-lead social factors that raise the risk of delinquincy
increase the number of subjects in the low lead/delinquent case group."
In other words, other factors pushing kids toward delinquency are more
frequently encountered by black teenagers than by white in this study
population. As a result, the pool of delinquent black subjects include
a larger proportion of teenagers whose delinquency was facilitated by
non-lead factors. This statistically dilutes the apparent strength of
lead's effect.
Most
importantly: "if other studies find a similar association between
lead and delinquency, a sizable segment of this important societal
problem would become accessible to primary prevention,"
i.e., reducing lead exposures.
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