Study of Amazonian Tribe Reveals the Key to Preventing Age-Related Brain Shrinkage
As we get older, our brains tend to shrink, making it harder for the brain to work correctly and increasing the risk for dementia, and scientists are not sure what triggers the changes that can lead to shrinking. But now, we have some new insight into the matter, thanks to a recent study published in The Journals of Gerontology Series A examining the brains of aging members of an Amazonian tribe that don’t shrink as fast as typically seen (1).
The Tsimane indigenous people of the Bolivian Amazon exhibit a significantly slower decrease in brain volume with age than populations in the U.S. and Europe. Such reduced rates of brain volume decrease, together with a subsistence lifestyle and low cardiovascular disease risk, may protect brain health even when up against substantial inflammation from infectious disease burden.
How you live your life determines how your brain ages
As we age, the brain starts to shrink and diminishes in size, which often comes with declining mental health and even dementia. Many risk factors could explain these changes. Among them, cardiovascular disease risk factors, whether caused by genetics, smoking, poor diet, or limited physical activity, seem to carry the most weight. That’s why high blood pressure and diabetes, conditions prevalent in industrialized countries, are common in patients who have significant brain shrinkage. That may explain why people with fewer of these risk factors should have a slower rate of brain shrinkage.
Advances in the study of aging have shown that one of the main drivers for aging and mental decline is inflammation. The Tsimane are known to have a high inflammatory load, a product of dealing with common illnesses in their harsh native environment. Researchers initially believed that these excessive amounts of inflammation might lead to an accelerated rate of brain shrinkage. However, the study’s results painted a more complex picture. There might be more to brain health than just inflammation.
Researchers tie brain shrinkage to cardiovascular risk factors
Led by a team of researchers based out of the University of Southern California (USC), Andrei Irimia and colleagues wanted to know how different lifestyles and environments could influence the long-term health of individuals and how risk factors could determine brain health in old age. To make a good comparison, they looked at data from the Tsimane people of the Amazon basin andcompared it to data from participants from industrialized cities in the U.S. and Europe.
The Tsimane have some of the lowest rates of cardiovascular disease in the world, which their lifestyle conditions can explain. Most Tsimane either farm, hunt, or fish, and have high levels of physical activity. Their diet is also very healthy and different from city populations. The Tsimane’s diet is unprocessed, rich in “good fats” like omega-3’s, and abundant with fiber. However, inflammation levels for the Tsimane are unexpectedly higher than those of the average city dweller.
Due to the nature of their environment, their immune systems work overtime to protect them from infections and parasites. For this reason, most Tsimane have very high rates of infections and chronic inflammation. Researchers found that the average Tsimane has high biomarkers for inflammation, which may increase the likelihood of brain shrinkage and dementia (2).
The unique characteristics of the Tsimane provided scientists with a great way to compare against what they usually see in city dwellers. One group has high levels of cardiovascular disease; the other group has chronically high levels of inflammation. Differences in brain size were examined by comparing CT scans from both groups of participants.
The researchers examined over 700 CT brain scans from the Tsimane and compared them to scans from people who lived in three major cities — St. Louis (U.S.), Hamburg (Germany), and Rotterdam (Netherlands). Overall, the Tsimane had lower rates of brain shrinkage compared to the scans of participants from the three major cities. Their results were eye-opening because they found that some risk factors may outweigh others regarding aging and brain health.
The scans also allowed the authors to take into consideration brain size and risk for mortality. The results showed a meaningful relationship between these factors — for each 1% increase in brain size, mortality risk decreased 5%.
Although their inflammation rates are higher, their healthy cardiovascular profiles have a protective effect that diminishes the expected rates of brain shrinkage. These findings are encouraging for people suffering from chronic inflammatory conditions or those concerned about their health in old age.
Essentially, the Tsimane’s healthier cardiovascular profiles protected their brains, even with increased inflammation. The authors conclude that improving lifestyle factors, like a healthy diet and increasing physical activity, may slow brain shrinkage.
- Irimia A, Chaudhari NN, Robles DJ, et al. The indigenous South American Tsimane exhibit relatively modest decrease in brain volume with age despite high systemic inflammation [published online ahead of print, 2021 May 26]. J Gerontol A Biol Sci Med Sci. 2021;glab138. doi:10.1093/gerona/glab138
- Walker KA, Hoogeveen RC, Folsom AR, et al. Midlife systemic inflammatory markers are associated with late-life brain volume: The ARIC study. Neurology. 2017;89(22):2262-2270. doi:10.1212/WNL.0000000000004688