Two Indigenous groups living in the Amazon rainforest have some of the lowest rates of dementia in the world, according to a new study.

The research, published today in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, could provide further clues about how sedentary, urban, and industrial lifestyles are a prime factor in the development of age-related dementia. The team also believes that these insights from the Indigenous Amazonians could also help teach others how to reduce dementia in the industrialized world. 

Scientists from the University of Southern California (USC) found that just 1 percent of older Tsimané and Moseten people, two Indigenous groups in the Bolivian Amazon, suffer from dementia. 

By stark comparison, up to 11 percent of people aged 65 and older living in the US have dementia. 

To reach their findings, the team studied hundreds of Tsimané and Moseten people using CT brain scans, cognitive and neurological assessments, and culturally appropriate questionnaires, aided by the help of a local team of translators and Bolivian doctors. 

Out of 435 Tsimané people, researchers identified just five cases of dementia and just one case among 169 Moseten people age 60 and over. 

To their surprise, the researchers found that older Tsimané and Moseten people with dementia frequently had unusual and prominent calcifications in the arteries buried within the skull. These strange calcifications were also seen significantly more frequently in those without dementia compared to European populations. The researchers weren’t sure what to make of this observation, but they hope to return to the Amazon for further investigation.

The research team doesn't point towards any genetic factors that may protect against dementia, but instead believes the key factor lies in lifestyle. 

It’s no secret that factors associated with industrialized urban living — midlife hypertension, diabetes, cardiovascular diseases, physical inactivity, poor diets, and air pollution — can significantly up the risk of dementia and Alzheimer’s disease.

It’s also well-known that these two Indigenous groups live exceptional healthy lifestyles in the Bolivian Amazon. Despite having little or no access to modern healthcare, the Tsimané are extremely healthy because they remain intensely physically active, using their bodies to fish, hunt, farm, and forage throughout their lifespan. Paired with this, they eat a high-fiber diet that is rich in vegetables, fruit, non-processed carbohydrates, fish, and lean meat.

This lifestyle clearly pays off in other ways. Previous studies have found that the brains of Tsimané people tend to age 70 percent slower than their Western counterparts. They also have remarkably healthy hearts and the lowest prevalence of coronary atherosclerosis of any population known to science.

While these points are well established, the precise reason for these groups' resilience to dementia is not clear. Nevertheless, the researchers believe it could offer some valuable lessons in the wider battle against dementia and Alzheimer’s. 

“Something about the pre-industrial subsistence lifestyle appears to protect older Tsimané and Moseten from dementia,” Margaret Gatz, lead study author and professor of psychology, gerontology and preventive medicine at the Center for Economic and Social Research at the USC Dornsife College of Letters, Arts and Sciences, said in a statement. 

“We’re in a race for solutions to the growing prevalence of Alzheimer’s disease and related dementias,” explained Hillard Kaplan, a study co-author and professor of health economics and anthropology at Chapman University who has studied the Tsimane for two decades. “Looking at these diverse populations augments and accelerates our understanding of these diseases and generate new insights.”