Keeping healthy brains as we age
The indigenous Tsimane people of the Bolivian Amazon might just have the healthiest brains on the planet. A new study from the University of Southern California has found their brains age far slower than their Western contemporaries. In fact, as they age they experience significantly less brain atrophy or wasting away. Atrophy is correlated with a greater risk of cognitive impairment, functional decline and dementia.
While those in industrialised countries have access to modern medical care, they are far more sedentary and eat a diet high in fat and sugar. By contrast, the Tsimane have little or no access to health care but are very physically active and consume a high-fibre diet that includes vegetables, as well as fish and lean meat.
“The Tsimane have provided us with an amazing natural experiment on the potentially detrimental effects of modern lifestyles on our health,” says study author Andrei Irimia, an assistant professor of gerontology, neuroscience and biomedical engineering at the university’s Leonard Davis School of Gerontology and Viterbi School of Engineering. “These findings suggest brain atrophy may be slowed substantially by the same lifestyle factors associated with very low risk of heart disease.”
The researchers enrolled 746 Tsimane adults, aged 40 to 94, in their study, which was published in The Journal of Gerontology, Series A: Biological Sciences and Medical Sciences in May.
They used scans to calculate brain volumes and then examined their association with age. (It took two days by river and road to get to the closest town with CT scanning equipment to do the scans.) Next, they compared these results with those in three industrialised populations in the US and Europe. The difference in brain volumes between middle age and old age was startling: 70% smaller in Tsimane than in Western populations. In other words, the Tsimane lose much less of their brain volume as they move from middle age to old age than do Westerners.
While the researchers did note the Tsimane have high levels of inflammation — which is typically associated with brain atrophy in Westerners — their study suggests that high inflammation doesn’t have a pronounced effect upon Tsimane brains. The Tsimane’s low cardiovascular risks may outweigh their infection caused by inflammation, raising new questions about the causes of dementia. One possible reason is that, in Westerners, inflammation is associated with obesity and metabolic causes. In the Tsimane, however, it is driven by respiratory, gastrointestinal and parasitic infections; infectious diseases are the most prominent cause of death among the Tsimane.
“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,” says study author Hillard Kaplan, a professor of health economics and anthropology at Chapman University who has studied the Tsimane for nearly two decades. “The Tsimane can serve as a baseline for healthy brain ageing.”
The Tsimane people captured scientists’ — and the world’s — attention when an earlier study found their elders to have extraordinarily healthy hearts. That earlier study, published in The Lancet in 2017, showed they 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 subsistence lifestyle of hunting, gathering, fishing and farming.
“The findings suggest ample opportunities for interventions to improve brain health, even in populations with high levels of inflammation,” Kaplan concludes.
PHOTO New Scientist