The lead-crime hypothesis and its effect on modern-day society.
Lead. It’s probably not something you have thought of in recent years. Back in the 1920s, it was used in gasoline to reduce engine knock and in paints to speed drying. Of course, a couple of decades later, the toxic effects were undeniable and lead was banned in these products.
Lead exposure was linked to a series of neurological disorders including aggressivity, impulsivity, ADHD, and lower IQ. Interestingly, these are the same traits that are often associated with young criminal offenders. It begs the question:
Could lead poisoning cause high crime rates?
In the 1980s, crime rates were at an all-time high. It was the wild wild west, with so many infamous serial killers such as Larry Eyler, Joseph Christopher, Richard Ramirez, Doug Clark, and Carol Bundy.
Many theories have attempted to explain the rise in crime during this era. The theories included economics, prison expansions, gun control, the crack epidemic, etc. While these factors likely played a part in the high crime rates in certain areas of the US, they do not fit the crime trends across the entire country (details discussed in this MotherJones article).
The lead-crime hypothesis
What does seem to fit the national trend is called the lead-crime hypothesis:
“Proposed link between elevated [lead] blood concentration in children and increased rates of crime, delinquency, and recidivism later in life”
Lead emissions, from leaded gasoline, were on the rise from the early 1940s through the early 1970s. As the health hazards became more apparent and leaded gasoline was replaced with unleaded, the lead emissions dropped (as explained in this paper from the National Center for Healthy Housing).
The crime rate trends look the same, except, they are shifted by 20 years. The crime rates climb from the 1960s through the 1980s, then drop back down starting in the 1990s. This trend was observed in all the major cities across the USA (and globally too— with confirmation in Australia, Canada, Great Britain, Finland, France, and many others).
Lead exposure during infancy
Children are most susceptible to absorbing lead from their environment. Lead poisoning causes developmental issues and aggressive behavior as the children mature. Once the children reach the formative years of young adulthood, they are more likely to participate in criminal activity (hence the 20-year shift in the lead-crime trends mentioned above).
There have been other studies confirming this hypothesis. A research group from Ohio followed a group of pregnant women with elevated lead concentrations in their blood. Their children were then studied from birth through to adulthood. The researchers found that the adults were more likely to participate in criminal activity if they had higher lead concentrations in their blood as infants.
Caveat: There are still many other factors that could be affecting the behavior of the children. Correlation does not always imply causation.
How lead affects the brain
Lead literally kills brain cells. It promotes what scientists call “apoptosis”, which means programmed cell death.
The other problem is that lead blocks the activity of calcium in the brain. Calcium is a “messenger” in the brain. The brain cannot communicate properly if lead is blocking calcium from sending signals between brain cells.
Lead also degrades myelin, which is a coating on the brain cell. This coating allows quick communication between cells. If the myelin becomes damaged or degraded, communication slows. Essentially, the brain is not working as it should, so lead-exposed children tend to have learning disorders and other neurological deficit issues.
Why are lead-exposed children aggressive?
There was a study out of the University of California (San Francisco) that found that the pre-frontal cortex was smaller in adults that were exposed to lead as young children. The prefrontal cortex is a part of the brain that’s responsible for mood regulation and decision-making, so these activities are impaired in lead-exposed adults.
Interestingly, this loss of gray matter in the front brain seemed to affect males more than females, which could explain why the crimes of the 1980s were mostly committed by young men.
Lead is still poisoning our children
Although crime rates have dropped from their peak in the 1980s, lead-based products continue to poison children. From 2014 through 2019, the city of Flint (Michigan), was struggling to get clean drinking water after their supply was contaminated with lead. During this time period, more than 5% of children tested had elevated lead concentrations in their blood.
Another large concern is old homes that are being remodeled. Homeowners unknowingly start to strip lead-containing paint from walls creating dust particles that can poison young children. The 2020 U.S. Census Bureau, American Community Survey shows that, in many states, a quarter of the houses are likely to contain lead-based chemicals. New York state is the worst with 33.6% of housing posing a risk for lead toxicity.
In the Los Angeles area, a 2017 Reuters Investigation special report found that over 5% of children showed elevated lead blood concentration, mostly due to lead-based paints, but also contaminated soil and water. The report found similar levels in both affluent and low-income neighborhoods. (Note: the report originally states 17% of children but this was later corrected to 5%)
What should we do about it?
Firstly, children need to be tested for elevated lead concentrations in their blood. Unfortunately, this is not something doctors routinely do anymore. We are quick to assume that a child with developmental or behavioral concerns was simply “born this way”.
Early identification and intervention of lead poisoning can significantly improve a child’s prospects. A study out of the University of Colorado focused on identifying and removing the cause of elevated lead in the children, then providing nutritional and educational support to the families. For very high blood concentrations, the children would also receive chelation therapies. They found that these early interventions decreased antisocial behaviors, such as suspensions and school crimes, as well as slightly increased their educational performance.
Lead is not the only problem
It is important to avoid blaming lead-poisoning for all criminal activities. It is likely a combination of economic and sociological factors that need to be improved.
However, even if removing lead does not significantly reduce crime, we are still removing a damaging toxin from the environment! That’s a win-win.