Contribution of childhood lead exposure to psychopathology in the US population over the past 75 years, 2024, McFarland et al

Contribution of childhood lead exposure to psychopathology in the US population over the past 75 years

Michael J. McFarland, Aaron Reuben, Matt Hauer

Background
More than half of the current US population was exposed to adverse lead levels in childhood as a result of lead's past use in gasoline. The total contribution of childhood lead exposures to US-population mental health and personality has yet to be evaluated.

Methods
We combined serial, cross-sectional blood–lead level (BLL) data from National Health and Nutrition Examination Surveys (NHANES) with historic leaded-gasoline data to estimate US childhood BLLs from 1940 to 2015 and calculate population mental-health symptom elevations from known lead-psychopathology associations. We utilized five outcomes: (1) General Psychopathology “points”, reflecting an individual's liability to overall mental disorder, scaled to match IQ scores (M = 100, SD = 15); (2) Symptoms of Internalizing disorders (anxiety and depression) and Attention-deficit/Hyperactivity Disorder (AD/HD), both z-scored (M = 0, SD = 1); and (3) Differences in the personality traits of Neuroticism and Conscientiousness (M = 0, SD = 1).

Results
Assuming that published lead-psychopathology associations are causal and not purely correlational: We estimate that by 2015, the US population had gained 602-million General Psychopathology factor points because of exposure arising from leaded gasoline, reflecting a 0.13-standard-deviation increase in overall liability to mental illness in the population and an estimated 151 million excess mental disorders attributable to lead exposure. Investigation of specific disorder-domain symptoms identified a 0.64-standard-deviation increase in population-level Internalizing symptoms and a 0.42-standard-deviation increase in AD/HD symptoms. Population-level Neuroticism increased by 0.14 standard deviations and Conscientiousness decreased by 0.20 standard deviations. Lead-associated mental health and personality differences were most pronounced for cohorts born from 1966 through 1986 (Generation X).

Conclusions
A significant burden of mental illness symptomatology and disadvantageous personality differences can be attributed to US children's exposure to lead over the past 75 years. Lead's potential contribution to psychiatry, medicine, and children's health may be larger than previously assumed.

Link (Journal of Child Psychology and Psychiatry) [Paywall]

 

I'm really skeptical about the reliability of measuring "Internalizing", "ADHD". "Neuroticism" and "Conscientiousness", to two decimal places, no less.

Can you go somewhere to get your internalizing measured? I'm pretty sure you could find a psychologist to give you a result such as "37.554", but I think most people here would have views about the actual value of that.

 

Wouldn't lead intake--and thus psychopathy--be strongly correlated to time spent near traffic? Those historical statistics should also be available, to further test the hypothesis.

 

I looked at how they measured these things, so you won't have to!

Internalizing Symptoms: The primary caregiver was asked whether, now or within the past 6 months, each of the following items were true of their adolescent: sudden changes in mood or feelings; feels or complains that no one loves him or her; feels worthless or inferior; is too fearful or anxious; and acts unhappy, sad, or depressed. Responses ranged from often (2), sometimes (1), or not true (0).

AD/HD Symptoms: The primary caregiver was asked whether now or within the past 6 months, the following items were true of their adolescent: can’t concentrate, can’t pay attention for long; can’t sit still, restless, or hyperactive; acts confused or seems to be in a fog; and is impulsive or acts without thinking. Responses ranged from often (2), sometimes (1), or not true (0).

Neuroticism Symptoms: The following statements were presented to respondents: Worries a lot, can be tense, gets nervous easily, is depressed or blue, can be moody, remains calm in tense situations(reverse-coded), is emotionally stable (reverse-coded), not easily upset (reverse-coded), Is relaxed (reverse-coded, handles stress well (reverse-coded). Answers ranged from disagree strongly (1), disagree (2), neither agree nor disagree (3), agree (4), agree strongly (5).

Conscientiousness Symptoms: The following statements were presented to respondents: does a thorough job, does things efficiently, makes plans and follows through with them, is a reliable worker, perseveres until the task is finished, is easily distracted (reverse-coded), can be somewhat careless (reverse-coded), tends to be lazy (reverse-coded), tends to be disorganized (reverse-coded). Answers ranged from disagree strongly (1), disagree (2), neither agree nor disagree (3), agree (4), agree strongly (5).

General Psychopathology: they measured this by extracting shared variance from multiple measures - the so-called p factor (although nowhere does it say exactly which measures they submitted to this analysis).

 

OK this is indeed pretty ridiculous. I cannot in any way reconcile the weird notion of "internalizing symptoms" as meaning whatever this is. It's meaningless argle-bargle, somewhere between Meyers-Briggs and Dungeons and Dragons character attributes.

 

Even if you don't agree with calling it "internalizing symptoms", is it not interesting that blood lead levels correlate to "sudden changes in mood or feelings; feels or complains that no one loves him or her; feels worthless or inferior; is too fearful or anxious; and acts unhappy, sad, or depressed"?

 

@Woolie can you check if they controlled for any confounders, like socioeconomic status?

 

Not really, since there are so many other factors involved. I recall the example of cancer rates correlating with living under powerlines. Those higher rates also correlated with similar economic status homes not under powerlines, so it was economic status (worse diets, less healthcare, etc) rather than the EMF. A similar factor may be involved with the lead study, with homes along high-traffic routes being lower economic status, or workaholics or whatever.

I have no confidence in studies based on poorly defined and hard to quantify factors. I suspect someone else could replicate the study and reach completely opposite conclusions, because it's too dependent on how you define and judge the things supposed to be measured.

 

I didn't realize I had intermittent AD/HD. Does that mean I have intermittent lead levels too?

Looking though that list again, wouldn't people living next to high-traffic routes have trouble concentrating, feel depressed, sad, etc, even without having elevated lead levels?