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Lead and Crime

by Steven Novella, Jan 14 2013

A recent article in Mother Jones discusses the potential role of lead in the increase in crime from the 1960s to the early 1990s, and the subsequent steady decline in crime rates since then. I have received numerous questions about this article and this possible connection between lead and crime. It is a well-written article, and an interesting question. Could one toxin really be responsible, among all the other possible causes, of the rise and fall in crime rates in the US?

Before we get to that, it’s interesting that this is not the first time in history this question has come up. There is a theory that the fall of Rome was due, in part, to chronic lead toxicity. The Romans used lead to make their water pipes (the origin of the word “plumber” as the root “plumb” refers to lead). But this was probably not the most significant source of lead for the Roman aristocracy, who also sweetened their wine and some of their food deliberately with lead. Analysis of lead levels in bones of burials from the time do show variable but often elevated lead levels, but the data is too scant to draw any firm conclusions.

They apparently knew of the toxic effects of lead, but thought that this was limited to acute lead toxicity – something that slave lead miners had to worry about, but not citizens. They did not think that low level chronic exposure was a risk, and apparently they were wrong.

However – there are problems with this nice story. Some scholars doubt that lead poisoning was as endemic in Rome as others claim. The evidence is complex. Lead was probably not added deliberately to wine, but wine was occasionally heated in lead containers. Terra cotta pipes were often used instead of lead for carrying water specifically because the risk of too many lead pipes was understood. And contemporary references in medical and veterinary writing make scant mention of lead poisoning, even though the syndrome was well recognized.

Beyond disagreements over the extent of lead poisoning in the Roman Empire, there is the far thornier problem of assigning cause to the fall of Rome. Most scholars criticize any attempt to find “the” cause of such a complex historical event, whether lead or anything else.

We find ourselves in a similar situation today. The Mother Jones articles centers around the rise and fall of crime from the 1960s to early 1990s in the US, and discusses research that argues that this rise and fall in the crime rate closely mirrors (although shifted by 23 years) the rise and fall of the use of leaded gasoline.

The article correctly points out that such ecological data is very difficulty to interpret. There are many potential factors that could correlate with the rise and fall in the crime rate. Confidence increases, however, when the correlation holds up in many possible ways. The article cites research by Rick Nevin and others showing that the correlation with environmental lead levels, mostly from leaded gasoline usage, holds up when compared state by state, city by city, and even by neighborhood. and also in countries other than the US. This makes the correlation much more compelling.

The literature seems to support a real connection between lead and crime. A recent review and study concluded that there is a correlation, and that lead levels in the air are predictive of crime rates, but especially when linked with resource availability. In other words, the effect of lead exposure on crime rate is greater when those individuals live in a neighborhood where they are less likely to be diagnosed and treated for lead poisoning, which makes sense.

There remains the possibility that lead exposure is just a marker for other variables that are truly the cause of crime. In other words – it’s possible that crime really has sociological causes, factors that also predict lead exposure. While this type of connection is probably true to some extent, it does appear that lead is an independent variable correlating with crime. Also a connection has been demonstrated with a prospective study, which partly controls for such confounding factors.

The lead connection is also biologically plausible, as it is well established that lead causes neurological changes including and increase in violence and decreased executive function.

While it is difficult to account for all possible confounding factors, the story that environmental lead exposure increases crime by causing chronic symptoms of violence and attention deficit is plausible and reasonably supported by existing evidence. The real question, it seems to me, is the magnitude of this effect, especially compared to other effects on crime.

The Mother Jones article, by Kevin Drum, cited a figure that 90% of the increase in crime since WWII might be due to lead. He was called out on this figure by blogger Deborah Blum, and Drum later printed a correction. He said the 90% figure is at the upper limit of the range of estimates, and that 50% is likely closer to the truth.

In the review I cited above, reference is made to research showing that “as much as 20%” of crime is “lead related.” One small point – Drum’s now 50% figure, as he points out, is the rise in crime, not the cause of all crime. The 20% figure cited in research is all crime – so these numbers may be compatible. Either way, the 90% figure likely overstates the connection.

Therefore, even accepting the 20% figure, that means 80% of crime has nothing to do (at least directly) with lead, and the sociologists are free to continue to speculate and study about the myriad of social causes of crime.

Conclusion

The connection between chronic lead exposure and neurological effects, including those that plausibly contribute to crime, is both plausible and reasonably supported by existing evidence. The magnitude of this effect is difficult to tease apart from the many variables that can potentially affect the crime rate. If we accept the 20% figure (crime that is lead related), which seems plausible, then this indicates a significant role for lead, but lead is certainly not the only important factor.

Also, because of the nature of this research there remains reasonable doubt about lead’s true role in the crime rate. This doubt, however, is not sufficient to argue that we should not pay attention to lead exposure or even take specific measures to limit it. The research is remarkably consistent in pointing to a real role for lead exposure. Multiple studies have also looked at the potential benefit of further reducing lead exposure (from soil and remaining lead pain, especially in window frames of old buildings). The research I can find all concludes that the benefit of lead reduction measures would be cost effective because of the potential benefits that would result.

Recommended Reading

32 Responses to “Lead and Crime”

  1. Daniel says:

    Sorry, but this argument is really flimsy. If you apply Occam’s Razor, the simplest explanation for the decrease in crime, especially violent crime, is the higher rates of incarceration. (I also agree with the argument that greater access to abortion has contributed also.) Yes, correlation is not causation, but there is a very close correlation between rates of incarceration and the decrease in crime. When you’re dealing with social phenomena, correlation is about as good as it gets. (“Social science” is not a science).

    You can also do the eye ball test as well. In countries with draconian criminal laws like Saudi Arabia (and I believe even the Soviet Union) there is a lot less violent crime. Violent crime in Miami has been at a tolerable level since the stepped up enforcement by the DEA against the drug gangs that operated there in the 80s and early 90s, when the city was a virtual war zone.

    Even if you agree with my premise, it doesn’t necessarily mean that the large number of people the US incarcerates is worth the cost. I can see it both ways though.

    • itzac says:

      http://www.csc-scc.gc.ca/text/rsrch/briefs/b29/b29-eng.shtml

      Here’s a study comparing crime rates between Canada, the UK, and the US between 1981 and 2001. Note that changes in crime rates track fairly closely between the three countries, despite only a fractional increase in incarceration rates in Canada and the UK compared to the US’ almost three-fold increase.

      #thatwaseasy

      • Daniel says:

        I briefly perused your link. Interesting, but I think you’re overstating the case. The decline in violent crime in the US was much greater during that time compared to the UK, which was either flat or ticked up a little bit.

        Canada tracks more closely, but I don’t feel it’s a great comparison considering that the violent crime rate in Canada was so much lower to begin with. Yes, the decline tracks closely between the two, but, even though I’m not a statistician, Canada’s decline seems less significant. Also, I’m obviously speculating, but since the countries share a border, the decline in the US might have something to do with the rate in Canada as well, although admittedly, you haven’t seen the same thing in Mexico.

    • vitriolix says:

      Incarceration rates are not very well linked with lowering crime. In fact the case is well made that more incarceration can lead to increased crime as throwing people in jail will harden them, make them move up the crime ladder. recidivism rates and the lack actual “corrections” in our corrections system make prisons a terrible tool for lowering crime.

      Your answer fails Occam’s Razor as even if you are correct, such a complex interaction is hardly a simpler answer than environmental toxins with a clear connection to impulse control and violence.

      • Daniel says:

        If you show me the evidence that says higher incarceration leads to more crime, instead of using the passive “the case is well made”, I would reconsider.

        Higher incarceration actually is a much simpler explanation than lead exposure, or the lack thereof. When criminals are in jail, they are not out in society to commit crimes. And, there is a strong correlation between higher incarceration and decreased crime.

  2. Todd says:

    http://www.freakonomics.com/2005/05/15/abortion-and-crime-who-should-you-believe/

    Probably a more practicle possiblility is that abortion became legal in 1973. Women who would have to given birth to children in an at risk enviroment now had another option. The crime rate dropped 17 years after the law was passed, about the time most kids start getting into serious crimes.

  3. There are many theories and correlations for crime – cops, prison, drugs, abortion, economic, etc. They probably all contribute. None, however, track as well with this one bump as does lead exposure.

    Still, I suspect lead is just part of a more complex picture. I don’t think there is any one variable that is predominant.

    I think the more practical question is – does the evidence warrant efforts to reduce lead exposure, and I think the answer to that is yes.

    • Daniel says:

      I don’t have the inclination to do a detailed cost-benefit analysis, but my gut tells me that reducing lead exposure is on the whole a good thing even though I think the link to crime is tenuous, at best.

      The only pause I have is that I’ve seen how the sausage gets made, namely through the efforts of plaintiffs’ attorneys, some of whom, shall we say, are less than scrupulous.

    • Steven Melendez says:

      I have to agree with Mr. Novella on this one. I have watched crime drop dramatically in New York. Yes, there has also been a decrease in other things than lead (for instance, no where near as much crack on the streets), but we were up to 2k+ murders per year in the 80’s. We are down to 90% that number. It coincides with not just the reduction of things like lead based paints, toys, etc, but also the reduction of some drugs. Also, being that lead is directly related to increased violence, I do think it warrants the effort to reduce/eliminate lead from day to day items. Do we need a “war on lead”… no, that is a waste of tax-payer dollars. Do we need to handle lead like we handle Asbestos? Absolutely.

  4. LREKing says:

    How long before we start speculating about the effects of all the mercury from CFLs that are disappearing into land fills?

  5. d brown says:

    Romans also used lead as commonly used makeup in both men and women. Much of the crime was from the new drug crack. By now even kids see what using it doses and they think users are fools.

  6. fordprefect says:

    I think this is a case of correlation != causation. I recently saw another great example that consisted of a graph with two data sets. One data set showed the increase in the number of autism diagnoses over a period of time; the other showed the increase in sales of organic foods over the same period. Both slopes lined up almost exactly. Organic foods causing autism is probably just as likely as lead poisoning causing societal violence.

    • tmac57 says:

      What would be the plausible cause for the organic/autism link?
      I know that you don’t really believe that,but you said “just as likely”,and Steven,being a neurologist by profession,believes that the lead/violence link is plausible:

      The lead connection is also biologically plausible, as it is well established that lead causes neurological changes including and increase in violence and decreased executive function.

      • fordprefect says:

        I do not dispute that lead causes neurological damage – I’m definitely not knowledgeable enough to argue that point with Steven. However, I’m not quite sure I can support an assertion that lead causes 20% of violence across a society. Lead levels may contribute in some way, and again, I trust Steven’s expertise when he postulates that it actually does. But, the fact that the crime levels did change over the period studied, and that lead was only one possible contributor, means that were a number of other factors at play.

        These other factors could be myriad and very wide-ranging, and very likely interact with one another in complex, hard-to-predict ways. At least that’s my impression, given my limited knowledge of sociology.

        I guess my point was that picking out actual contributing factors is fraught with potential false causative links. I’m guessing, but there could well be a correlation between crime rates and just about any other environmental factor, too, like CFC levels in the atmosphere or PCB levels in drinking water. Something as complex as changing crime rates in a constantly evolving society just can’t be boiled down to simple causes. To echo comments in some subsequent posts, it seems very difficult to set up a well-controlled experiment at the societal level.

      • Steven Melendez says:

        I don’t think it is an assertion. It is, at this time, yes a correlation based theory. I am sure as more evidence comes through, it will be seen that the “damage” from lead is greater than we know, or less than thought. One way or another at least. However, bear in mind a side effect of lead is increased levels VIOLENCE. That, plus the graphic data does equal correlation with evidence.

        Tell you what, though. Maybe we can setup a small town somewhere to test the theory on whether lead can cause a rise in crime… I don’t think so. I have a funny feeling that going with the correlation in this case is probably the best idea. It is good to continue to build evidence towards it. It’s not like this is being done via psuedo-science Mr. Prefect. It is based on observable evidence both with time based data and medical assessments.

      • fordprefect says:

        I agree – a correlation arrived at by valid methods is definitely NOT pseudo-science. I hope that this correlation leads us to more research that will further our knowledge and possibly help us mitigate societal violence.

  7. James says:

    I’m getting a little tired of the line “Correlation is not causation”. I see it everywhere on the web from people skeptical of the lead-crime connection. If one performs an experiment, say a drug trial, in which all other variables are controlled, correlation is indeed good evidence of causation – especially if one has a plausible hypothesis to explain the causal mechanism. The studies of the link between crime and lead, involving many different populations of different sizes, could almost be considered a world wide controlled experiment.

    If one could show that the same people who ate organic foods as children are the ones now being diagnosed as autistic it would be good evidence of a causal relationship. Although it seems unlikely!

    • Daniel says:

      You cannot do a controlled experiment in “social sciences”.

    • tmac57 says:

      James,you are correct that the saying is sometimes misused.
      It really should be stated as “Correlation is not necessarily causation”.
      We still need to be careful not to leap to conclusions though.

      • James says:

        When I compared the situation to a controlled experiment, I was being figurative. One of the commenters I read on another site put it more or less like this, “If God were to perform a controlled experiment on the effects of lead exposure on society, He would do it this way.”

        The commenter below implies, I think, that blood lead concentration and crime might have a shared cause, urban poverty. However, if you read the original article (“Lead: the Real Criminal Element” on Mother Jones), it cites evidence that crime rates in different sized cities, that used to be far apart. have now closed. The naive assumption that higher crime is just of fact of city life seems to have been disproved.

        Seriously, you should take a look at the original posting. And does anyone have a better explanation for why crime has declined so dramatically since the early nineties. not only in the US but around the world. including New Zealand where I live?

      • Daniel says:

        Actually, crime, or at least violent crime, hasn’t uniformly declined worldwide. An earlier comment linked to a study about incarceration/crime rate in the US, Canada and the UK. Declines or no change during that time in the US and Canada, but steady increases in the UK.

        So far as the link to lead exposure, NYC, and even one of the most dangerous cities in the US, Chicago, saw homicides and other violent crime decrease dramatically since the early/mid 1980s. Again, I’m not a statistician, and I don’t have the inclination to an in depth analysis of the study, but I find it very hard to believe that those decreases can even be a significant product of decrease in exposure to lead.

      • DarMan says:

        Daniel, why is this so hard to fathom? One of the reason we know about the impact of lead paint is due to the behavioral impact it has on children — more violent, and detached.
        I am perplexed by your comments. You say that you are not a statistician, and you seem to listen to your “gut” quite a bit. This is a theory that argues that 20-30% of the reduction in crime we have witnessed correlates to lead. The author on this blog is a “skeptic” and a clinical neurologist at Yale. I assume that his “gut” also was suspicious of the claim. The difference between his gut and your gut seems to be that he actually did some work reading the many scholarly papers that have been written on this theory and he found the argument plausible. You seem to be troubled by complicated linkages. Note that since the advent of Easypass, there has been a dramatic reduction in low birth weight and other fetal syndromes in neighborhoods around major toll booths. That initial linkage is simple enough to understand, but someday I am sure that the reduced toxicity of this change will impact other aspects of the community. If you cannot be swayed by scientific studies, then you are simply stubborn. If you choose to comment, I propose you do a bit more reading on the topic, because the basic evidence is compelling. You are free to follow your “gut”, but if that is your only guide, then spare us the prolonged details.

  8. MadScientist says:

    “In other words, the effect of lead exposure on crime rate is greater when those individuals live in a neighborhood where they are less likely to be diagnosed and treated for lead poisoning, which makes sense.”

    For me it doesn’t make sense unless you first assume that increased lead concentration in blood resulted in increased crime – which is what needs to be proved. I agree that lead levels in blood may simply be a marker for something else – for example the size of a city (big city = more traffic = more tetraethyl lead and combustion products in the air) and larger cities tend to have higher crime rates especially as the numbers of desperately poor people increases. Just another correlation – nothing to see here.

    • Steven Melendez says:

      As I stated above to Mr. Prefect, there is a direct link of increased lead exposure to increased violence. This fact coinciding with the decrease in lead to the decrease in crime (especially violent crime), can be considered correlation, yes, but it really does boil down to the theory that lead reduction can in fact lead to a reduction in crime. No one is stating all crime is reduced by reducing lead, but I can see how a small percentage, 10… maybe 15… maybe even 20 % can be related to it. There is positive evidence pointing towards it. I think it is something that should be studied further. If there is nothing to see here, would you then say the reduction is meaningless, and we can continue to use lead based paints, toys, etc.?

  9. Archie Clebberdale says:

    Even if we take the whole story at face value… given that crime has many different causes you simply cannot say that 20% of the data points are caused by lead. Maybe it was lead that pushed them over the threshold, but of course lead could only have done so in conjunction with the other factors.
    If a man with a highly criminal mind set but who (barely) wouldn’t have committed a crime without lead in his environment, commits a crime, does that mean the lead made him do it? I don’t think so.

  10. A Barnes says:

    Would that theory explain what is happening in Mexico? And Africa? Are there studies about those countries?

  11. Angela Smith says:

    Let’s speak with freedom, it’s a good act and good start to stop maltreatment. But somehow at some point we need to put limitations and follow the by laws. Let’s start to support programs for anti crime. At the same time us parent’s should make way to protect them. I saw a smart phone app anytime our grownups could ask help in a press of panic button to ask for help. they could also bring to 911 escalation if it’s too serious.

  12. Verimius says:

    I wonder if there are any other positive social effects of the reduction in environmental lead? Are people getting generally smarter because of this? Is ADHD declining? Surely the reducing crime rate is not the only positive effect. Are there any others?

  13. DarMan says:

    Daniel, I am perplexed by your comments. You say that you are not a statistician, an you seem to listen to your gut quite a bit. This is a theory that argues that 20-30% of the reduction in crime we have witnesed correlates to lead. The author on this blog is a “skeptic” and a clinical neurologist at Yale. I assume that his “gut” also was suspicious of the claim. The difference between his gut and your gut seems to be that he actually did soe work reading the many scholarly papers that have been writtien on this theory and he found the argument plausible. You seem to be troubled by complicated linkages. Note that since the advent of easypass, there has been a dramatic reduction in low birthweight and other fetal syndroms in neughborhoods around major toll booths. That initial linkage is simple enough to understand, but someday I am sure that the reduced toxicity of this change will impact other aspects of the community. If you cannot be swayed, then you are simply stubborn. If you want to comment, I propose you do a bit more reading on the topic, becasue the basic evidence is compelling. You are free to follow your “gut”, but if that is your only guide, then spare us the details.