Prevalence of Dementia in Indigenous Bolivians: Insights from Epidemiological Studies

UC Santa Barbara

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It is an imperative that has been confirmed repeatedly in recent decades: it is necessary to disentangle the relative contributions of traditional and well-known risk factors, such as diet and physical activity, along with less studied ones (infection, air pollution and isolation social) to better understand how lifestyle affects our risk of dementia and other chronic diseases of aging.

Michael Gurven(link is external), professor of anthropology and chair of the Integrative Anthropological Sciences Unit at UC Santa Barbara, has been working to do exactly that by collaborating with indigenous communities in South America for more than two decades.

A new paper from an international team of researchers including Gurven and collaborators from USC and Chapman University, published today in Alzheimer’s & Dementia : The Journal of the Alzheimer’s Association(link is external), highlights the deep relationship between lifestyle and cognitive health. Their study reveals that two indigenous groups native to the Bolivian Amazon, who practice a subsistence lifestyle of slash-and-burn agriculture, fishing, hunting and gathering, have one of the lowest rates of dementia in the world.

The researchers found that among older people in Tsimane and Moseten, only about 1% suffer from dementia. In contrast, 11% of people age 65 and older living in the United States have dementia, according to the Alzheimer’s Association.

“Many assume that dementia was rare in our ancestral past, mainly because few survived to age 80, when dementia becomes most visible,” said Gurven, who is co-director of the Tsimane Health and Life History Project. link is external)(THLHP), funded by the National Institute on Aging. "But even with this large sample of older adults, we just don’t see Alzheimer’s disease."

"Something about the non-industrial subsistence lifestyle seems to protect the older Tsimane and Moseten from dementia," said Margaret Gatz (link is external), senior author of the study and professor of psychology, gerontology and preventive medicine at the USC Dornsife College of Letters, Arts and Sciences Center for Economic and Social Research.

The researchers used brain computed tomography (CT) imaging, cognitive and neurological assessments, and culturally appropriate questionnaires, facilitated by a local team of trained bilingual Tsimane research assistants and Bolivian physicians, to diagnose dementia and cognitive decline among the Tsimane and Moseten.

The new study found only five cases of dementia among 435 Tsimane and only one case among 169 Moseten aged 60 or older.

In the same age groups over 60, the research team diagnosed about 8% of Tsimane and 10% of Moseten with mild cognitive impairment (MCI), which is usually characterized by an early stage of memory loss or decreased another cognitive ability, such as language or spatial perception. MCI is often considered the stage between normal cognitive aging and more severe dementia. The study authors noted that these rates are more comparable to MCI in high-income countries like the US.

The researchers were surprised to discover that study participants with dementia or MCI frequently had unusual, prominent calcifications of their intracranial arteries. These participants frequently showed parkinsonian symptoms during neurological examinations and cognitive deficits in attention, spatial awareness, and executive functioning.

Although calcifications were more common among people with cognitive impairment, the researchers also observed these vascular calcifications on CT scans of people without dementia or mild cognitive impairment. They say more research is needed to understand the role of vascular factors, as well as infectious and inflammatory disorders, which are very common in these populations, along with other dementia risks.

Comparing dementia between indigenous groups

The approximately 17,000 Tsimane remain very physically active throughout their lives, and most of the food they eat comes from their work in the forest. The 3,000 Moseten also reside in rural villages and engage in subsistence agricultural work. Unlike the more isolated Tsimane, they live closer to cities and have schools, access to clean water and medical services, they speak fluent Spanish and are more likely to know how to read and write.

The study authors compared their results with a systematic review of 15 studies of indigenous populations in Australia, North America, Guam and Brazil. That previous review found a prevalence of dementia ranging from 0.5% to 20% among Indigenous older adults.

The fact that indigenous populations in other parts of the world have high rates of dementia may be due to a greater amount of contact and adoption of lifestyles from their non-indigenous neighbors.

They also face increased risks of diabetes, hypertension, alcohol abuse, obesity and cardiovascular disease.

These risk factors for dementia are extremely low among the Tsimane and Moseten populations. Previous research published in The Lancet showed that Tsimane people have extraordinarily healthy hearts in old age and the lowest prevalence of coronary atherosclerosis (a disease that manifests itself as fatty deposits within the arteries) of any population known to the world. science. This distinction may be related to their subsistence lifestyle.

“That some indigenous populations, such as in Australia, show high rates of dementia, while we show very low rates in the Bolivian Amazon,” Gurven said, “suggests that when lifestyles change radically, indigenous populations may be at risk. even greater risk of dementia and other modern scourges than their non-indigenous neighbors.”

Other studies published in 2021 showed that the Tsimane and Moseten show minimal atrial fibrillation, another indicator of healthy hearts, and less brain atrophy(link is external) than their American and European peers.

Researchers say that unlike the Tsimane, lifestyle factors in higher-income countries, including a sedentary lifestyle, diets high in sugars and fats, and altered immune system regulation due to exposure reduced to different types of parasites, contribute to heart disease and can also accelerate brain aging.

A race for solutions to Alzheimer’s disease

Aging is the most important known risk factor for Alzheimer’s disease and other dementias. Converging evidence points to low formal education, hypertension and diabetes in mid-life, cardiovascular disease, physical inactivity and, more recently, air pollution as the main modifiable risk factors for dementia and Alzheimer’s disease. Alzheimer’s.

The aging of the world’s population, coupled with the proliferation of such modifiable risk factors, will lead to a tripling of the number of people with dementia worldwide by 2050, to more than 152 million , according to estimates.

“We are in a race to find solutions to the increasing prevalence of Alzheimer’s disease and related dementias,” said Hillard Kaplan, co-senior author and professor of health economics and anthropology at Chapman University, and co-director of THLHP. "Looking at these diverse populations increases and accelerates our understanding of these diseases to help generate new knowledge."

The international team is currently revisiting the villages of Tsimane and Moseten to follow up on those who were previously tested and look for new cases. “We are also exploring whether Tsimane and Moseten have any genetic protection against cognitive aging. "We are also trying to better understand how vascular and infectious processes may contribute to the intracranial calcification that, surprisingly, was so common in most adults."

"Despite these and other risk factors, the fact that dementia is rare among both the Tsimane and the more acculturated Moseten suggests that a healthy, active lifestyle can really make a difference."