A time before dementia?

Dementia afflicts around 900,000 people in the UK, and an estimated 55 million people worldwide. For a baby born in the UK today, their lifetime risk of developing Alzheimer's disease or a related dementia is, as things stand, a staggering 1 in 3. But has dementia always been such a scourge? A new review of texts from Ancient Greece and Rome, in the Journal of Alzheimer's Disease, suggests that it hasn't; the authors argue that there are lessons to learn from this — but firm conclusions are difficult to draw.  

Caleb E. Finch at the University of Southern California, US, and Stanley M. Burstein studied the writings of Greek and Roman authors, starting with Hippocrates in the 4th century BC, and the 'Hippocratic' texts that followers continued for a century after Hippocrates' death. "We could not find any mention of memory loss in [sic] elderly in this major body of ancient medical writing," the authors write. Meanwhile, Aristotle, who was also working in the 4th century BC, wrote about cognitive ageing in 'older men' — but his only reference to severe memory loss was in people who were close to death. Based on their analysis of these texts, Finch and Burstein conclude that memory problems that today might be diagnosed as Mild Cognitive Impairment were present in this period in Greece, but that more extensive dementia was not. 

Four centuries later, though, Ancient Roman writers describe cases that seem closer to our picture of dementia — though they seem to be rare. The first probable advanced case of Alzheimer's or a similar dementia appears in a text by Pliny the Elder, who died in AD79, the authors write. In this text, Pliny describes a senator who had forgotten his own name. Then, in the following century, the writer Juvenal first used the term 'dementia' to describe severe memory loss in elderly people. Also in the 2nd century AD, the Greek doctor Galen mentioned cases of elderly people with clear memory problems. But for Galen, mental decline, when it happened, typically began after the age of 80.  

The authors conclude that there were instances of dementia in Ancient Rome, though they seemed to be uncommon. They suggest a few possible reasons for the emergence of these cases: the use of lead — which research shows increases Alzheimer's risk — in wine and water pipes, and also air pollution, which studies also show increases dementia risk. 

Finch and Burstein argue that all of this suggests that our modern lifestyle is the main reason for the current dementia crisis. To support their case, they also highlight data from studies of the Tsimane, a hunter-gatherer population in Bolivia. 

Compared with Brits or Americans, for example, the Tsimane have lower blood glucose levels and lower cholesterol (both of which are linked with a reduced risk of Alzheimer's), as well as a slower rate of age-related thinning of the cerebral cortex — which again is linked to dementia risk. Dementia is are also relatively rare among the Tsimane, affecting 1.2% of people aged over 60, compared with 8% of over-60s in the US and 6.2% in Europe. The researchers believe that, taken together, their findings support the idea that Alzheimer's and related dementias are diseases of modern environments and lifestyles.  

Certainly, there is plenty of work linking a lack of exercise, obesity, dysfunctional fat metabolism, exposure to air pollution, and Type 2 diabetes to an increased risk of Alzheimer's and related dementias. So it would be surprising if the highly active, low-sugar Tsimane lifestyle wasn't protective. 

However, as data included in the paper indicates, rates of Mild Cognitive Impairment (which can precede Alzheimer's) for the Tsimane at age 60 are about the same as for the US. In fact, lifestyle/environmental factors alone probably don't fully explain the differences in dementia risk now for us versus the Tsimane — or, by extension, for us versus people living in ancient Greece. 

Yes, the prevalence of dementia in over-60s is far lower for the Tsimane, but Alzheimer's risk increases significantly with advanced age — and there are proportionately far more much older people in the US than in the Tsimane population. 

The modal age of death for the Tsimane is only 72, compared with 85 in the US. And data on dementia prevalence in the UK shows that about 3% of people aged 70-74 are affected, compared with 18.3% of people in their 80s. That jump in risk, in combination with a longer average lifespan in the US and Europe, could go a long way to explaining why dementia is far more common in Brits (or Americans) aged 60+ than it is among the Tsimane. Typical lifespans in ancient Greece and Rome would likely also have been shorter than ours — so, this could have explained (or gone a long way towards explaining) the relative lack of cases of dementia in the ancient world. 

None of this means that a lack of exercise, diabetes, air pollution and so on, don't contribute to Alzheimer's risk. There is clear evidence that they do. And the finding of reduced cortical thinning in the Tsimane does suggest that their lifestyle and/or environment are protective. But advanced age is the biggest known risk factor for dementia — and this new paper has not changed that picture. 

Read the paper in full.