More than six million Americans of all ages have Alzheimer’s. About one in ten people age 65 and older has this devastating neurodegenerative disease. While scientists’ understanding of Alzheimer’s has improved dramatically over the past decades, we still don’t know exactly what triggers it. There is presently no cure.

A new study is complicating Alzheimer’s further, suggesting that this form of dementia may be a distinctly modern phenomenon. Researchers at the University of Southern California (USC) scoured classical medical texts from ancient Greece and Rome and could barely find mentions of symptoms consistent with a dementia diagnosis. This challenges the notion that Alzheimer’s is a timeless affliction but also hints at the profound impact of modern lifestyles on the prevalence of dementia.

Dementia in Antiquity

Caleb Finch, a distinguished professor at the USC Leonard Davis School of Gerontology, and historian Stanley Burstein scoured the works of Hippocrates and his successors, as well as later Roman texts, for mentions of symptoms we would now associate with dementia.

The researchers found that the Greeks acknowledged that aging could bring with it some degree of memory impairment, akin to what we would today classify as mild cognitive impairment (MCI). Yet, there was no indication of the more profound memory, speech, and reasoning losses that define Alzheimer’s.

It wasn’t until Roman times that references to what could be interpreted as dementia began to surface, albeit sparingly. Notable mentions include Galen’s observation of learning difficulties in the elderly and Pliny the Elder’s account of a senator forgetting his own name. “Elderly silliness … is characteristic of irresponsible old men, but not of all old men,” Cicero casually mentions in one of the surviving texts.

These accounts are valuable medical records of cognitive decline in the ancient world, but they rarely show up. The mentions certainly don’t stack up with the dementia epidemic we’re witnessing today.

“The ancient Greeks had very, very few — but we found them — mentions of something that would be like mild cognitive impairment,” said Finch, a University Professor at the USC Leonard Davis School of Gerontology and first author of the new study.

“When we got to the Romans, and we uncovered at least four statements that suggest rare cases of advanced dementia — we can’t tell if it’s Alzheimer’s. So, there was a progression going from the ancient Greeks to the Romans.”

Could dementia be largely caused by a post-modern lifestyle?

The research proposes a compelling argument that dementia could largely be a product of modern environments and lifestyles. Finch suggests that the densification of Roman cities and the consequent rise in pollution, along with the use of lead in cookware and water pipes, may have contributed to an increase in cognitive decline and subsequent mentions in medical texts. Roman aristocrats most often used cups and cutlery made of lead, a powerful neurotoxin. They even added lead acetate to their wine to sweeten it.

You may argue that Alzheimer’s was rare in antiquity simply because there weren’t that many old people to begin with — and you wouldn’t be wrong. In his book The Economic History of the Greco-Roman World, Walter Scheidel estimates half of the Roman subjects died by the age of 10. Of those still alive at age 10, half would die by the age of 50. In his work Old Age in the Roman World: A Cultural and Social History, Professor Tim Parkin from the University of Melbourne estimates 6-8% of the population in the Roman world in the first century C.E. was age 60 or older. For comparison, around 17% of the U.S. population is over 60, according to a 2020 census.

Alzheimer’s symptoms typically start to show at age 65 and older. Since not a lot of people reached this age in the Roman world, this may explain the lack of mentions consistent with dementia symptoms in ancient medical texts.

But that may only partly explain the findings. Finch’s hypothesis isn’t some baseless speculation because we also have modern evidence that there may be something going awry with our post-industrial lifestyle that may be connected to Alzheimer’s in some way.

In 2022, researchers led by Margaret Gatz, a professor of psychology, gerontology and preventive medicine at the University of South California, traveled deep into the Amazon jungle. There, they studied the Tsimane people of the Bolivian Amazon, whose preindustrial lifestyle mirrors that of ancient civilizations from thousands of years ago.

The Tsimane number about 16,000 people living in mostly riverbank villages scattered across about 3,000 square miles of the Amazon jungle. They are forager farmers who fish, hunt, and cut down trees with machetes, which keeps everyone very physically active throughout their lifetimes.

The neighboring Mosetén, which number around 3,000 and have close cultural ties with the Tsimane’, reside in rural villages and rely on subsistence agricultural work. However, they live closer to towns, have schools, and access to health posts, as well as access to roads and electricity.

The researchers found just 5 cases of dementia among 435 Tsimane aged 60 and over, and one case among 169 elderly Mosetén. This is much lower than the rate of incidence in Western countries.

In high-income countries with high rates of dementia among older adults, the population generally does not engage in the recommended amount of physical activity and has a diet rich in sugars and fats. As a result, older adults are more susceptible to heart disease and brain aging. In contrast, the Tsimane people have unusually healthy hearts for their age. That’s not surprising considering they also have the lowest prevalence of coronary atherosclerosis of any population in the world.

In 2021, the same team from the University of South California found that the Tsimane indigenous people of the Bolivian Amazon experience less brain atrophy than their American and European peers. Their decrease in brain volume happened at a rate that was 70% lower than in Western populations.

Ancient people in antiquity, whether in Rome, Greece, or Egypt, would have also engaged in a lot of physical work to keep their pre-industrial societies running. Like the Tsimane, their non-sedentary lifestyles may explain the lack of medical mentions of dementia, with compelling ramifications for how we treat dementia and Alzheimer’s today. Moreover, the research invites us to reconsider how we view the health of ancient civilizations and the lessons they might still teach us about living well.

The new findings appeared in the Journal of Alzheimer’s Disease.