Roman Empire's use of lead lowered IQ levels across Europe, study finds
164 comments
·January 7, 2025peeters
vasco
Could also happen that all the advances in hygiene and infrastructure and logistics during the Roman empire had a more positive impact on IQ than the negative effect of lead. Not starving while growing up does wonders for the brain.
biggoodwolf
What did the Romans ever do for us?
BSDobelix
I dont know who "us" is, but probably roads and writing?
martin_a
I mean, I guess the aqueduct was a nice thing?!
kragen
Probably not in the parts of Europe outside the Roman Empire and definitely not in the peoples that the Romans killed all of.
bell-cot
Plenty of people starved...just not (in their better centuries) the better-off Romans.
For (presumed) IQ benefits, I'd focus more on the hygiene, and the relatively disease-free drinking water which all those lead pipes & lead-lined aqueducts provided. (Plus the sewers.) There were lots of nasty diseases you could catch by drinking the water in ancient cities. And at scale, "lead lowered IQ" isn't much different to "unable to think well while ill", to "higher mortality makes education a poorer investment".
panick21_
That a very reductive view. Data shows that during the Roman empire, people moved on mass from hill forts into the flatlands (presumably giving better acess to agroculture, trade and water). We also see far more material culture, and not just for rich people. Huge amount of just common consumer goods, and this even streches far beyond the borders of the empire itself. Population also increased during this time.
PeterHolzwarth
Fully agree, @peeters - as I've mentioned elsewhere in these comments, there's a long-standing trend of trying to identify the one true cause of the fall of the Roman Empire. Each explanation falls short - it's just a complicated thing (and heck, the empire didn't really fall, it just shifted east.)
hodgesrm
Or as some wag once put it, the empire then continued to decline and fall for another 1000 years.
gazchop
Inclined to agree with this. It didn't fall, just sort of withered into other cultural ideologies and empires.
Some of it was also fucking bananas which didn't survive enlightenment.
tankenmate
Something a lot of people don't realise is that the last of the "Roman" states (that called themselves Roman) didn't cease until about 50 years before Columbus crossed the Atlantic (xref the fall of Constantinople).
SMP-UX
This is one of the problems with modern academia. It's hard to extrapolate these things
watwut
The guardian article is not academia.
gazchop
Oh it's really easy to extrapolate stuff. But perhaps they shouldn't. A lot of papers I've seen recently have wild romantic extrapolations based on cherry picked correlations.
Some of the social sciences are terrible at this. A former partner was a researcher in one of what I now consider to be less respectable fields and she would come up with a feely conclusion and fit the data to it and publish it. Wanted me to co-author one with her and do the statistical analysis. Told her I don't want to be on Retraction Watch.
Anotheroneagain
That could explain how the lead poisoning crowd took over. No, there won't be any retractions, you will be "educated" that you are stupid, "anti science", and too stupid to understand the newly discovered "fact".
UltraSane
It is perfectly reasonable to assume lead would affect people 2000 years ago the same way it does today. Human biology hasn't changed.
me-vs-cat
1. Lactose Tolerance: The ability to digest lactose as adults evolved in populations with a history of dairy farming, such as those in Europe, the Middle East, and parts of Africa.
2. Disease Resistance: Genetic adaptations to diseases like malaria (e.g., sickle cell trait) have become more common in certain regions.
3. Skin Pigmentation: Variations in skin color have continued to adapt to UV exposure in different regions, influenced by migration and interbreeding.
4. Height and Physique: Improved nutrition and health care have led to an increase in average height and changes in body composition in many populations.
5. Wisdom Teeth: A gradual decrease in jaw size has made wisdom teeth less functional, and they are increasingly absent in some populations.
6. Brain Function: While the brain's size and structure remain unchanged, shifts in cognitive demands and education have influenced how we use our brains.
-- https://let-me-ChatGPT-that-for-you/search?q=how+has+human+b...
UltraSane
And none of that is at all relevant to how lead affects the human brain and so is completely useless. You should have asked it "Would lead lower IQ in humans 2000 years ago the same way it does today?" This is what DeepSeekv3 says:
Yes, lead exposure would have likely had similar detrimental effects on human cognition and IQ 2000 years ago as it does today. Lead is a neurotoxin that interferes with the development and function of the brain, particularly in children. Its harmful effects on intelligence, behavior, and overall health are well-documented in modern studies, and these effects would have been the same in the past, even if they were not understood at the time.
kennyloginz
What a horrible reference. I hope this doesn’t become a thing.
rat87
Would have implies they didn't use lead buy if they had it would have lowered IQs
May have lowered IQs based on extrapolation and modern studies
Might be a better way to put it
peeters
Both are valid ways of using "would have", in this case I'm using it as the past tense of "will have". But I appreciate the ambiguity it creates.
> We use "would have" as the past tense form of will have:
>> I phoned at six o'clock. I knew he would have got home by then.
Note the difference between this and:
> I phoned at six o'clock. I knew he was home by then.
Which implies first-hand knowledge of his location. The first only signals a logical conclusion.
https://learnenglish.britishcouncil.org/grammar/english-gram...
guerrilla
> models to presume some levels of cognitive effects.
Not "presume", "deduce" or "conclude".
curmudgeon22
> On average, lead levels in children’s blood at the peak of the Roman empire could have risen 2.4 micrograms per decilitre, the researchers found, reducing their IQ by 2.5 to 3 points. When taking background lead into account, childhood blood levels may have reached about 3.5 micrograms per decilitre.
> A 2021 study by the Centers for Disease Control and Prevention in the US found blood levels in children aged one to five years fell from 15.2 to 0.83 micrograms per decilitre between the late 1970s and 2016 as leaded fuels were banned.
rayiner
Wow. We mock those stupid Romans for putting lead in their drinking water supply, but we literally vaporized it and had everyone inhale it for decades so it'd go straight to the bloodstream.
0_____0
Still do :) all the GA piston planes flying above you are still running leaded fuel.
cjrp
The majority, but not all - some run on UL91 or even "mogas" (unleaded fuel from the petrol station).
mistrial9
> we literally vaporized it and had everyone inhale it for decades
this is a massive scandal that has not been fully understood in public AFAIK. Extensive documentation of the false premise of leaded gasoline has been published, e.g.
https://www.thenation.com/article/archive/secret-history-lea...
nahnahno
2.5-3 micrograms per deciliter is nothing. Wouldn’t even come up as elevated by current childhood screening guidelines. I very much doubt 2-3 IQ point difference.
cma
That's the average, so it would be much high the cities in the cities than rurally right?
HeatrayEnjoyer
I wouldn't call it nothing.
Current regulation requires water supply at the tap to measure <10 µg/L, changing to <5 µg/L next decade.
2-3 µg/L is significant.
s1artibartfast
You are comparing level in the blood and water.
elcritch
Worse the parent says 2-3 μg/dL or 20-30 μg/L right?
thaumasiotes
> reducing their IQ by 2.5 to 3 points
I seem to recall reading an article that observed that every time we do a study of the effect of lead exposure on IQ, it gets larger.
IQs aren't changing much, but lead exposure is going down, and so we keep imputing the same IQ gaps to ever-smaller quantities of lead.
trimethylpurine
IQs aren't changing much
Isn't IQ a comparative representation of one's standing within their contemporary age group?
My understanding is that within a given group the median should be 100. So you won't see it change between groups. This is highly relevant when you're talking about different groups being exposed to different concentrations of lead.
As an extreme example to make the point, if people born in 1970 were all exposed to high concentrations of lead and were all morons as a result, their median IQ is still 100.
Then people born in 2000 are exposed to far less lead and are super smart, but their median IQ would still be 100.
Points above or below 100 are merely a specification of how many fractions of a standard deviation above or below that median within the given age group a person's performance is measured to be.
That said, even within a group, 2.5 - 3 points seems largely insignificant as an individual's score might vary more than this depending on which day of the week they took the test. It seems a big stretch to draw any scientific conclusion from such a small variance.
somenameforme
You're right about how IQ is measured with 100 being the average and, generally, 15 points being a standard deviation. But numerous tests also record raw scores and these can be compared between generations. Scandiland and other places with compulsory conscription + IQ testing are the goldmine here. This is what led to the observation of the 'Flynn Effect' - the observation that IQ between generations was increasing, and later to its apparent reversal that generally started sometime around 1990 in the developed world. [1] That paper reports a later date, because it's about America in which studies on this topic lagged substantially behind Europe.
It's not easily explained by things like immigration since it is also present (though less pronounced) even within families. The hypothesis I find most compelling is that IQ levels have "naturally" been declining for decades, but improvements in nutrition, education, etc were helping to offset, and even rise beyond, these declines. But as nutrition, education, etc reach the point of diminishing returns, the declines dominate.
[1] - https://www.sciencedirect.com/science/article/pii/S016028962...
Anotheroneagain
>Then people born in 2000 are exposed to far less lead and are super smart,
What do you base this on?
lostmsu
AFAIK, no, 100 IQ points at 25 and 18 or any other age are the same "brain power".
thaumasiotes
You're basically right about the relative nature of IQ scores, but you're wrong about the comparison being drawn.
To impute the effect of lead, you look at a bunch of people, measure the amount of lead in their blood, measure their IQs, and see how much of a difference there is between people with a lot of lead and people with less or none.
Modern poor people who live in crummy areas where there's still a little bit of lead are about as stupid, relative to the leadless elite, as poor people from decades past who lived in crummy areas which, at the time, had a lot more lead than they do now.
It seems like a safe assumption that the effect of lead on people with negligible lead levels has stayed constant over the decades at indistinguishable-from-zero.
But for lead to explain the gap between the lead-haves and the lead-have-nots, its effect must have increased dramatically over that same period. That gap hasn't changed. But lead levels have plummeted.
bpodgursky
People are downvoting, but yes this is accurate.
There are confounders between houses with lead and other demographics and contribute to the gap and aren't completely controlled — aspects of social class and low mobility that are hard to explicitly capture, it's all old housing.
So as the lead level drops and the gap remains steady (increasingly dominated by the confounding factors), more and more IQ gap gets attributed to the small lead-level gap between those living in old housing with abated lead pipes + paint and new pipes + new paint.
luxuryballs
[flagged]
SteveNuts
Why specifically call out fluoride?
lolinder
It's a bit of a thing with a particular political persuasion in the US right now (RFK Jr has made his anti-fluoride position a big part of his deal for his future role as Secretary of Health and Human Services), and there was a report in the news recently that some see as backing up the claims against fluoride:
https://www.latimes.com/science/story/2025-01-06/what-a-new-...
It's not as conclusive a study as some people might claim, though:
> For starters, 52 of the 74 studies were judged by the report authors to have a “high risk of bias.” That undermines the validity and reliability of their results.
> Another issue is that most of the studies considered fluoride exposures far above the target level for the U.S. ... Only seven of the studies assessed children whose water contained less than 1.5 mg/L of fluoride. When they were considered on their own, there was no relationship between fluoride exposure and IQ.
luxuryballs
“Why specifically call out lead?”
-Julius Caesar, 45 BC
luxuryballs
Didn’t studies come out connecting it to lower IQ? Places are pulling it or planning to pull it, nothing to do with RFK.
cameronh90
It's an international Communist conspiracy to sap and impurify all of our precious bodily fluids.
CyberDildonics
Lots of people across the world don't have fluoride in their water, you could compare populations right now.
davorak
I doubt you can do a clean comparison, likely too many confounding factors, at least to pull anything out easily.
PeterHolzwarth
I have no idea if this is true (and honestly can only barely remember the reference, which I read maybe a decade or two ago), but I believe I saw a comment that the interior of lead pipes eventually develop a "calcified" (don't know what else to call it) lining of the lead reacting to water, such that lead stops leeching into the water that passes through the pipes.
I believe this came up when reading something about how the trend of traditional historicity has always been to identify the Big Major Cause of the fall of the Roman empire, but that each explanation ultimately falls short. The followup point made by this, of course, is two-fold: that "falls" are often very complex and multi-faceted; and that the Roman empire never really "fell" in the Gibbons sense - it just slowly evolved, and eventually shifted east, finally becoming self-consciously retro-classically Hellenized, and just morphed to something new and lasted another thousand years -- but never actually fell during that time.
Anyone else have any thoughts or insight on the "lead pipes eventually line themselves with something non-lead-like" angle?
WorkerBee28474
I haven't read it, but the book History of Toxicology and Environmental Health [0] would say that pipes were not a problem. Preparing food and wine in lead containers could have been a problem, but it wasn't until centuries after the Roman Empire "fell" that doctors even described the symptoms of lead poisoning.
And to throw in another quote from a scholarly source, "Water from the river Anio, which fed two of Rome's principal aqueducts, the Aqua Anio Vetus and Aqua Anio Novus, was particularly hard and conveyed high levels of dissolved calcium carbonate. Indeed, Frontinus complains in his treatise on the aqueducts of Rome, that "the accumulation of deposit, which sometimes hardens into a crust, contracts the channel of the water" (CXXII.1)." [1]
[0] https://www.sciencedirect.com/book/9780128153390/toxicology-...
[1] https://penelope.uchicago.edu/encyclopaedia_romana/wine/lead...
PeterHolzwarth
I hope I can be forgiven for replying to myself, but at this timestamp, I've got three excellent replies affirming the "lead pipes get gunked up and it stops being a notable problem" concept.
Thanks for the replies! Great stuff from all of you.
matwood
> would say that pipes were not a problem.
You obviously would prefer non-lead pipes, but running the water for a period before using flushes out any lead if the pipes are in the house. Like you say in your comment, it's when water sits in a container like a wine vat where leeching has time to accumulate.
PeterHolzwarth
That's a great reply, thanks, and seems to align with the "pipes just get clogged up" concept I read some time ago.
timschmidt
It's called mineralization, and happens so long as there are dissolved minerals in the water and PH is correct. Lead contamination happened in Flint, MI because additives to control the water PH were neglected to save cost, and slightly acidic water ate away at the mineralization layer in the pipes and began dissolving the lead again.
AngryData
I don't know if I would call Flint's water just "slightly" acidic. It was acidic enough for the Flint hospital to complain about their stainless steel sinks rusting, for local automotive plants to dig their own wells because it was destroying parts they were washing, and turned their entire water supply system into swiss cheese that had to be replaced. It might be slightly acidic compared to highly concentrated acids, but in terms of potable water it seems extremely corrosive.
timschmidt
Of course you are right, and no offense meant. I grew up in Flint, and have family there to this day. My intention was more to communicate that even small changes in water PH can affect this mineralization layer.
What I rarely see talked about with regard to Flint's water supply is that Detroit was willing to give them water for free, which is documented, and the only explanation that makes sense as to why they weren't taken up on the offer is the state governor's cabinet connections to fracking and a pipeline intended to bring lakewater inland to facilitate fracking. They wanted the taxpayers of Flint to help foot the bill. See: http://banmichiganfracking.org/the-flint-water-connection-to...
pea
Yes, the piping in my parents’ house is all lead, but not worth replacing due to the above. It’s pretty common in old houses in Britain
martinpw
Very interesting. I recently found out the house I grew up in in the UK over 15+ years had lead pipes that were never replaced, and I always wondered why they were not replaced and if it had some cognitive impact. This lining effect likely explains the reason, and offers at least some reassurance.
lostlogin
If the water PH changes, the value in replacing those pipes might become more apparent.
adzm
But my sweet water!
alexey-salmin
I wonder how did you figure out this is the case, did you make any tests of the water?
I can hardly imagine living in a house with lead pipes. I mean even if water if provably safe today, what if tomorrow PH shifts to acidity.
userbinator
I have some late-19th-century books on plumbing that mention the same passivation layer, and so clearly it was known, along with some of the toxic effects of lead, back when it was widely used for plumbing (which I must also mention that the 'plumb' comes from 'plumbum' - Latin for lead.)
Ekaros
Also when talking about downfall. I think it is also sensible question timeframe when these materials were first used. Was that during raise of empire or after it? As it feels wrong that something that had been used for generations during formation of empire would lead to downfall...
f1shy
There must be something, as I grew in a house with lead pipes, and while I will not disclose my IQ or that of my siblings, they are high. Or maybe we were lucky? Of course only anecdotical data.
Ferret7446
I can't help but be pedantic and point out that since IQ is normalized, their average IQ would be 100 whether or not they used lead.
More philosophically, the condition of life is inherently susceptible to damage, so you practically have to draw the line at what level of damage you want to try and mitigate given the realities of the time. Do you want to be wrapped up, only breathing, eating, and drinking perfectly calibrated mixes of chemicals?
xeonmc
Who are you, who are so wise in the Ways of Science?
lifeisstillgood
> A 2021 study by the Centers for Disease Control and Prevention in the US found blood levels in children aged one to five years fell from 15.2 to 0.83 micrograms per decilitre between the late 1970s and 2016 as leaded fuels were banned.
So if my generation had lead levels 3-4 X higher than Roman kids, does this explain the “Exams are getting easier” meme - that exams are staying the same, but kids really are getting smarter …
( also the hey exams were waaay harder in the Edwardian Era meme?)
Anotheroneagain
Exams are getting easier, because children are getting dumber, and wouldn't pass if they stayed the same.
caymanjim
I find it hard to believe that atmospheric lead levels were higher in the ancient Roman Empire than since the Industrial Revolution. The amount of lead mined and smelted now is vastly more than it was then. Regardless of current safety measures, there were decades with none. And then we had leaded gasoline for a century.
Everything in this article may be accurate, but that likely means we're all far worse off now.
o999
> By some estimates, the Roman empire amounted to more than 80 million people at its peak, meaning that about a quarter of the world’s population could have been exposed to the lead pollution generated by mining and smelting. The effects of lead poisoning can be so severe that scholars have debated whether it contributed to the fall of the empire.
I wonder what will happen to current empires from micro- and nano-plastics, PFAS, airpolution, as well as harmful yet popular habits like doomscrolling and games addictions.
leptoniscool
I wonder if future historians will see a similar drop after widespread use of plastic
__MatrixMan__
Maybe, but given that "plastics" are a broad category I'd expect that IQ would me a poor proxy for some of their effects.
BPA for instance, is a xenoestrogen. I'm not sure what metric to watch for it, but it's probably not IQ.
sebmellen
Anogenital distance is likely the preferred measure.
> Males with a short AGD (lower than the median around 52 mm (2 in)) have seven times the chance of being sub-fertile as those with a longer AGD.
> Swan et al. report that the levels of phthalates associated with significant AGD reductions are found in approximately one-quarter of Americans tested by the Centers for Disease Control and Prevention (CDC) for phthalate body burdens.
https://en.m.wikipedia.org/wiki/Anogenital_distance (warning on the header photos).
__MatrixMan__
I was imagining something a bit more impactful (and easy to find in the data), because as far as that one goes, it's not clear why anyone should know or care.
Maybe high school graduation rate (an inverse proxy to indicate bullying)?
pseudolus
Perhaps not with respect to IQ but there’s a chance that future historians might correlate the use of plastics with increased rates of infertility.
echelon
Perhaps there is a link between plastics and ADHD [1].
TomK32
I find it interesting that the article you linked didn't mention the heritability of ADHD. In around 3/4ths[0] of cases ADHD is caused by genetics, which leaves plenty of space for other causes.
User23
Next do fluoride.
That’s been “debunked” though right?
User23
For those that didn’t get the memo: https://www.cnn.com/2025/01/06/health/children-higher-fluori...
Beijinger
TomK32
Oh gosh... "insidious castration of all men" and "blurred gender roles". Really? They have been blurry for all of homo sapiens existence, just think of the matriarchal societies that still exist today[0]. Gender dysphoria has been documented from individuals[1] for a long time, societies accepted a third gender since ancient time and even in the USA, the Cercle Hermaphroditos[2] was quite early to the party, being founded in 1895 (yes 130 years ago).
I'm confident that plastic will go the way trees did: Unbothered for a long time until bacteria figured dead wood is just another food and put a stop to trees being fossilized as coal.
Stop plastics, it's a good idea to do so for many reasons, but there's no need to drag gender roles and those stupid good old times into it. I much prefer spending time with my kid instead of slaving away 9-5 six days a week.
[0] https://www.townandcountrymag.com/society/tradition/g2856528... [1] https://en.wikipedia.org/wiki/Kalonymus_ben_Kalonymus [2] https://en.wikipedia.org/wiki/Cercle_Hermaphroditos
defrost
It doesn't seem as if the principal researcher behind this result is a historian:
Mistletoe
Has plastic been linked to lower IQ?
userbinator
If anything, the correlation might be the opposite --- look at plasticiser use in East Asian countries, for example.
glitchc
Not yet, I think the OP means it might in the future.
SMP-UX
Roman lead pipes were not a significant factor on the health of humans back then... To the same extent as public sewers, bathing, hygiene rules etc. Rome had it a lot better than even some countries today. Yeah you still had to deal with infections and such which could have been deadly but time and medicine era that you were in you had way better health outcomes in Rome
Symbiote
You seem to have missed the third paragraph of the article.
ashoeafoot
Its more about lead kettles in which a sweet whine/ sugary additive was boiled down?
null
thinkingemote
Original paper https://www.pnas.org/doi/abs/10.1073/pnas.2419630121
-----
Note this isn't mainly about lead pipes:
"most significant... may have been through background air pollution from mining and smelting of silver and lead ores "
baud147258
> smelting of silver and lead ores
The smelting of silver and lead is detectable via ice cores, I remember seeing a graph showing the height of Roman silver production was only matched in the 18th century https://en.wikipedia.org/wiki/Roman_economy#/media/File:Worl...
deadlast2
Would love to see a similar study on fluoride in modern civilizations.
BorgHunter
Fluoride has two major differences that would complicate such a study: First, fluoride is a natural component of lots of drinking water (often at levels far higher than artificial fluoridation creates), while lead contamination in drinking water is rare and usually human-caused. Second, lead is known to be bad for one's health in any amount, while fluoride is only known to cause IQ drops above a certain dose.
You might find this meta-analysis interesting: https://jamanetwork.com/journals/jamapediatrics/fullarticle/... Part of that conclusion (note that water fluoridation in the US is recommended to a level of 0.7 mg/L):
> This systematic review and meta-analysis found inverse associations and a dose-response association between fluoride measurements in urine and drinking water and children’s IQ across the large multicountry epidemiological literature. There were limited data and uncertainty in the dose-response association between fluoride exposure and children’s IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L.
animal531
Is a 2-3 point IQ drop really that terrible?
If we all suddenly went from 100% to 97% brain efficiency we wouldn't even notice. For example a bad night of sleep is surely worth 10 times as much.
f1shy
Or even measurable reliably? What is the typical error bar for an IQ test? Also is only kind of estimation based on what is known today about lead...
> Roman Empire’s use of lead lowered IQ levels across Europe, study finds
I'm not a fan of this phrasing. None of the findings had anything to do with measuring IQ levels in ancient Europe. They were about measuring historical levels of lead, which they then just plugged into modern models to presume some levels of cognitive effects.
A study that was actually able to measure cognitive disparities and correlate them with measured levels of lead would have been extremely interesting, but this is not that. Everything other than the measurements of historical lead levels seems to be fluff.
This would kind of be like saying "massive asteroid strike 100m years ago lead to cataclysmic tsunami, study finds" but then not showing any evidence of a tsunami, just evidence that it struck an ocean and the inference that that would have caused a tsunami. It might be a reasonable inference, it's just not as interesting as the title would make it seem.
Edit: I should qualify, I'm not trying to say that "they did the math"-style papers don't have value, just that the phrasing in how they are presented matters to me. If the phrasing was more like "Use of lead in Roman Empire would have lowered IQ levels across Europe, study finds" I would have no issue with it.