January 5, 2013

Lead Astray


A recent and interesting article at the investigative MotherJones magazine discusses links between crime rates and the prevalence of lead emissions, touting the latter as America's Real Criminal Element. A follow-up also noted interesting connections involving lead paint.

Kevin Drum does a good job of convincing readers that, rather than political measures being responsible for falling crime rates, the gradual decline of crack use or increased incarcerations, the rather counterintuitive proposal that said rates have dropped due to the gradual withdrawal of leaded petrol. According to Drum, there is a
"growing body of research linking lead exposure in small children with a whole raft of complications later in life, including lower IQ, hyperactivity, behavioral problems, and learning disabilities."
And among the more important neurologically relevant observations, Drum made special note of a PLOS study; Cecil et. al (2008) found that lead exposure had in fact contributed to reduced/decreased myelination. Myelination refers to the process by which neurons are surrounded by a layer or sheath of myelin, a type of fat that both insulates the neuron and allows for faster transmission and complex communications, and accounts for the composition of the brain's "white matter". Lead exposure was to be a factor in causing a degrading alteration in myelin organisation. In other words, less myelination leads to less co-ordination and slower connections as the neurons will not be communicating effectively.

The same study used MRI-scanning to determine the effect of lead poisoning on the whole brain. Neuronal loss was found in various areas such as the cognitive and emotional areas of the anterior cingulate cortex, regions associated with "general intellectual and executive functioning, antisocial behaviors, and attention deficit hyperactivity disorder (ADHD)". Poor scores were found in physical movement tests too, but by far the largest and most serious finding related to a permanent reduction in grey matter, specifically in the medial part of the pre-frontal cortex. According to one of the researchers, Kim Cecil, lead poisoning affected precisely the brain areas "that make us most human", as the pre-frontal cortex is associated with the brain's executive functions; emotion regulation, impulse control, attention, verbal reasoning and mental flexibility.

These findings certainly deserve attention although, as Deborah Blum (Pulitzer Prize-winning journalist and science writer) noted in her response, the research has been covered before, both by Drum (Jan 2012) and other authors/publications, including the Washington Post back in 2007. What makes this article different is Drum's seeming enthusiasm to attribute up to 90% of crime to lead exposure and poisoning. As Blum notes,
"does it trump drugs, poverty, urban gang warfare, education, and other such issues to the point that they account for a bare ten percent of the crime statistics? That's a harder case to make, partly because as Drum himself notes correlation is not causation: the fact, for instance, that falling crime follows a pattern of falling lead exposure doesn't rule out many other influences."
Blum also brings a calming elucidation to the worrying neuroscientific findings as well, stating that, while it is true that lead exposure may lead to significant neurological deficits, it is much more complicated than as simply thought. For instance, reduced myelination can also be down to malnutrition and other environmental factors, and also that research into the situation hasn't yet produced any indication of a clear biological pathway through which exposure to lead can influence individuals to become antisocial and criminal.

As well as indicating other sources of lead that could cause concern, there is agreement that increasing evidence does point to lead as being a significant threat to health and that further research could increase the knowledge and evidence base through which solutions can be found.

If you have time, go take a look at Drum's article. Aside from the '90%' issue (that has since been corrected) it is littered with links to research, making it an edifying and extremely interesting read.


  1. Welcome back to the blogosphere!
    Interesting article, decreased lead exposure does not seem to have been given much consideration in previous discussions of secular trends, such as rising IQ or falling crime rates.

  2. Thanks very much!

    Yes that's true, probably because it sounds so outlandish at first glance. Although I think Drum did a great job putting his case together and underpinning his main points with links to research.