Leaded Gasoline and Mental Health

by Brian Dunning
March 4, 2025

In December of 2024, headlines shouted that leaded gasoline had caused some 150+ million mental health cases in just the United States alone. That's a huge number. The population of the United States is 340 million; nearly half of us have a mental illness that was caused by leaded gasoline? If that sounds a little sketchy to you, count me right there alongside. It seems to be a thing that is crying out for us to point our skeptical eye at it. Did leaded gasoline cause mental health problems, and are the numbers really that high?

In the 1920s, it was discovered that adding tetraethyl lead to gasoline reduced engine knock and improved engine performance, and it quickly became widely used all over the world. Scientists, meanwhile, cautioned that this would cause lead poisoning; but they had little control over the automotive fuel industry. Predictably, within decades, studies began finding that there was not only higher levels of lead found in the blood of Americans, but also that it was increasingly being found environmentally, particularly in the soil near roads and highways.

Every puff of automotive exhaust released lead particles into the air. It settled into the soil near the road, but over time that contaminated soil yielded lead-laced crops. Wind and debris and people walking around accumulated leaded dust particles, which then found their way to schools and homes and supermarkets and warehouses and offices. People living in those environments thus inevitably built up lead in their bodies, via multiple pathways.

One of the problems with lead is that it has four stable isotopes, a trait which is unique among the heavier elements. ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb are formed as uranium and thorium decay naturally; and ²⁰⁴Pb is the primordial form of lead. Those four isotopes of lead never go away or decay or change, since they are stable. Once they get into the environment, they stay there. Lead is persistent — including when it gets into your body.

The peak of leaded gasoline came in the 1970s, as the gasoline industry continued growing but when the use of lead began to be phased out. During this period, it was found that the average blood lead levels in American children aged 1-5 reached 15.2 µg/dL (micrograms per deciliter) for the period of 1976-1980. How high is that? Compare it to today, three decades after the banning of leaded gasoline in the United States, when children aged 1-5 have a blood lead level of just .83 µg/dL. At the peak, it was almost 20 times higher than it is now.

So, a knee jerk reaction to that would be that children who lived through that peak would be some 20 times more disabled than children today. Right? Make sense?

But, being an experienced person of a skeptical bent, I knew that it's the dose that makes the poison. We all have tiny amounts of every toxic substance known to science in our bodies, simply because we live in the world and entropy is a thing. Most compounds of concern have established safe levels. So I, knowing that I don't know, wondered what is a safe level of lead in the blood. How many micrograms per deciliter can you have, and not have to worry about it? Because we will all always have some non-zero amount. Were children in the 1970s experiencing a level that was truly of concern, or was it just a scary-sounding number that was actually below risky levels? And the same question applies to today's much lower number. Is that also a dangerous level? Or is it a safe level?

In 2012, a CDC committee (the Centers for Disease Control and Prevention) called the Advisory Committee on Childhood Lead Poisoning Prevention filed a report which found that "No safe childhood blood lead level can be identified." So let's interpret what that means. It doesn't mean that any lead at all is harmful; it means we don't know how much lead you need to have before harm begins. We found harm at every level. In such a situation, if you want to be safe, all you can do is to minimize the exposure as much as possible.

So — again — being an experienced person of a skeptical bent, I decided there were three questions I wanted answers to:

1. How much lead would one expect to have in their body from normal natural sources, even assuming leaded gasoline had never existed;
   
   
2. Via what vectors would one expect to receive that lead contamination; and
   
   
3. What harm would that lead do to me?

Let's take these one at a time. First, how much lead would the average person have in their body just by living on Earth?— which we could consider a normal level. The fact is we don't know. It wasn't until the 1950s that we developed the technique of atomic absorption spectrometry, which is how we measure blood lead levels. And by then, leaded gasoline had been in use for 30 years. So that's when researchers said, whoa, we'd better start systematically measuring and recording these levels. It was already on a steep upward curve.

That takes us to the second question: Via what vectors would one expect to receive lead contamination? Historically, lead paint has always been the best-known culprit. But lead in paint is actually pretty well sequestered. It would have required a kid to sit and chew on the windowsill in their bedroom, and actually swallow the paint, to get any into their system; which I'm freely willing to admit I did. But the total amount I ever swallowed was certainly less than a teaspoon, of which only a miniscule percentage was lead.

The dominant vector was not that, but household dust. Tracked in by shoes, and by breezes through open windows. All of that dust carried stable isotopes of lead. A somewhat distant second was dinner, mainly in the form of vegetables grown in soil contaminated with the settling of lead particles from automotive exhaust.

Now it's important to note that this lead would have gotten into your body whether you were a child or a senior. What matters is a complex calculation of how much lead was in the environment, how many years of your life you spent in such an environment, and at what age you were when it was at its highest. All of this combines to determine how much lead reached your brain, and how much time it had to do its evil work.

And this takes us to our third question: what harm that lead would have done. Well, here we have a simple answer to a complicated question. But it's big, and you should probably sit down and prepare yourself for it.

Let's start with what lead actually does to you. There are about six basic mechanisms by which lead in the blood impairs brain function:

1. It interferes with neurotransmitter chemicals, thus messing up the signaling pathways that normal brain function relies upon.
   
   
2. It can mimic the presence of calcium ions, which play a critical role in neuron development and signaling. This disruption affects cognitive functions like learning, memory, and behavior.
   
   
3. This one is complicated, but it generates compounds that promote oxidative damage, which can impact lipids, proteins, and DNA. This oxidative damage often kills neurons.
   
   
4. The presence of lead inhibits the function of certain enzymes which govern the synthesis and degradation of neurotransmitter chemicals. This definitely messes with normal brain function.
   
   
5. Lead induces apoptosis in neurons, which tells them when to die. In early brain development, such as in a young child, this creates irreversible long-term deficits in brain function.
   
   
6. The presence of lead inhibits the formation of synapses between neurons and the genesis of new neurons, resulting in reduced complexity and connectivity in the brain. When this happens in a young developing brain, it produces irreversible long-term functional deficits.

When you put all of this together, what you get is impairment of the dopamine system, meaning people are no longer properly rewarded or motivated; damage to the prefrontal cortex, meaning people end up with reduced impulse control; and shrinkage of the hippocampus, meaning people are less able to form memories; and reduced amounts of gray matter in brain regions associated with emotional regulation. None of that is good.

To put it in even more stark terms, what we've seen in studies comparing lead-exposed populations to non-lead-exposed paints a pretty grim picture. The populations with more lead exposure exhibit:

• More neurosis, i.e., less emotional stability;
• Reduced levels of conscientiousness;
• More disagreeable, i.e., less socially cooperative;
• Higher risk tolerance; and
• Lower skills at conflict resolution.

Basically sounds like it turns people into modern social media alpha-male influencers.

And this isn't just conjecture or my personal opinion; as always, scroll to the bottom of the web transcript for this episode for all the authoritative sources, references, and further reading suggestions to support all of this. This is all published research in proper peer-reviewed journals.

And this is the perfect place to circle back around to that 2024 study cited at the top of the show, claiming that 151 million Americans — about half the population — suffered a reduced IQ or some other mental illness as a result of increased lead exposure during their most developmental years, all stemming from leaded gasoline. And it's not just this one published study; it's been independently replicated multiple times.

The peak of the bell curve for reduced brain function struck those born from 1966 to 1970, when the burning of leaded gasoline was at its peak. These people have an average IQ six points below where it ought to be. The broader body of the bell curve stretched from the late 1960s to the mid 1980s; anyone born during those years, and to a progressively lesser extent during the years on the long tails of that curve, has also suffered from reduced developmental brain function.

When we examine this cohort of Americans born from 1966 to 1970, we find three diagnoses making up the majority of that 151 million cases. They are:

1. Generalized Anxiety Disorder, with an increased rate of 1.75 times the average;
   
   
2. Major Depressive Disorder, with an increased rate also of 1.75 times the average; and
   
   
3. ADHD, Attention-Deficit/Hyperactivity Disorder, with an increased rate of 1.17 times the average.

These numbers include only those who are diagnosable. What they don't include is the probably much larger number who don't develop diagnosable conditions, but who may still experience subclinical symptoms or enhanced vulnerability to stressors.

So, yeah: For once a scary headline was actually spot-on. If you know a Gen Xer, give them a hug.

By Brian Dunning
Follow @BrianDunning