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Scientists looking for a way to fight Alzheimer’s have found valuable clues about how to fight the memory-destroying condition in the Amazon rainforest.
Researchers have identified a tribe living in the Bolivian Amazon whose brain volume decreases some 70% more slowly than Westerners as they age.
Researchers say the healthy diet and active lifestyle of the Tsimane people of the Bolivian Amazon could explain the massive difference.
Brain atrophy – or a loss of brain cells – is a symptom associated with Alzheimer's disease and dementia.
While brain scans show the Tsimane have similar levels of brain inflammation – a symptom thought to be a sign of mental decay – their brains stay healthier.
The researchers behind the finding believe that, as they don't have access to modern medicine like their European counterparts, their diet and lifestyle is the most likely explanation.
The Tsimane are extremely physically active and eat a high-fibre diet, including vegetables, fish and lean meat.
Previous research has also shown the tribespeople have a very low risk of heart disease in comparison to Europeans.
The findings have been published in Journal of Gerontology, Series A: Biological Sciences and Medical Sciences.
The new study was led by Dr Hillard Kaplan, Professor of health economics and anthropology at Chapman University, in the United States, who has studied the Tsimane for nearly two decades.
He said: "Our sedentary lifestyle and diet rich in sugars and fats may be accelerating the loss of brain tissue with age and making us more vulnerable to diseases such as Alzheimer's.
"The Tsimane can serve as a baseline for healthy brain ageing.
"This study demonstrates that the Tsimane stand out not only in terms of heart health, but brain health as well.
"The findings suggest ample opportunities for interventions to improve brain health, even in populations with high levels of inflammation."
The researchers scanned the brains of 746 Tsimane adults between the ages of 40 to 94.
Many of the study participants had to travel from remote villages to Trinidad, Bolivia, the closest town with CT scanning equipment. That journey could last as long as two full days with travel by river and road.
The team used the scans to calculate brain volumes and then examined their association with age for Tsimane.
Next, they compared these results to those in three industrialised populations in the United States and Europe.
The scientists found that the difference in brain volumes between middle age and old age is 70 per cent smaller in Tsimane than in Western populations.
This, say the researchers, suggests that the Tsimane's brains likely experience far less brain atrophy than Westerners as they age – atrophy is correlated with risk of cognitive impairment, functional decline and dementia.
The researchers noted that the Tsimane have high levels of inflammation, which is typically associated with brain atrophy in Westerners.
However that high inflammation does not have a pronounced effect upon Tsimane brains.
According to the study authors, the Tsimane's low heart disease risks could outweigh their infection-driven inflammatory risk, raising new questions about the causes of dementia.
One possible reason is that, in Westerners, inflammation is associated with obesity and metabolic causes whereas, in the Tsimane, it is driven by respiratory, gastrointestinal, and parasitic infections.
Infectious diseases are the most prominent cause of death among the Tsimane, the researchers explained.
Dr Andrei Irimia, a researcher at the University of Southern California, said: "The Tsimane have provided us with an amazing natural experiment on the potentially detrimental effects of modern lifestyles on our health.
"These findings suggest that brain atrophy may be slowed substantially by the same lifestyle factors associated with very low risk of heart disease."
The indigenous Tsimane people captured scientists' attention when an earlier study found them to have extraordinarily healthy hearts in older age.
That prior study, published by the Lancet in 2017, showed that Tsimane have the lowest prevalence of coronary atherosclerosis of any population known to science and that they have few cardiovascular disease risk factors.
The very low rate of heart disease among the roughly 16,000 Tsimane is very likely related to their pre-industrial subsistence lifestyle of hunting, gathering, fishing, and farming.
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