Compared to industrialized counterparts Tsimané people of lowland Bolivia have less food availability and must expend more effort to get it
Photo Credit Michael Gurven
Scientific Frontline: Extended "At a Glance" Summary: Dementia Incidence in the Tsimané and Mosetén
The Core Concept: A longitudinal study reveals that the incidence rate of dementia among the Tsimané and Mosetén Indigenous communities in lowland Bolivia is comparable to Western populations, despite their significantly lower overall prevalence of the disease.
Key Distinction/Mechanism: While initial cross-sectional studies showed low dementia prevalence (a snapshot of existing cases), longitudinal tracking of incidence (new cases over time) showed similar rates to industrialized nations, suggesting the low prevalence is due to individuals not living long after disease onset rather than a lower baseline risk of developing it.
Major Frameworks/Components:
- Epidemiological Metrics: Distinguishing between incidence (new cases) and prevalence (existing cases).
- Neurological Pathology: Dementia in these populations presents differently from typical Alzheimer's disease, showing vascular contributions to cognitive impairment rather than amyloid or tau protein indicators.
- Genetics: The APOE e4 gene variant was identified as a strong risk factor for dementia, alongside advanced age.
- Socio-Ecological Context: The high mortality rate following dementia onset is hypothesized to stem from the inability to contribute to food production in a food-scarce environment, limited medical care, and insufficient familial caregiving capacity.
Branch of Science: Epidemiology, Gerontology, Anthropology, Neurology Genetics.
Future Application: The findings emphasize the need for ethnographical study of caregiving and the daily lives of cognitively impaired elders in non-industrial settings, and prompt further investigation using improved brain imaging and biomarkers to understand vascular injury and Alzheimer's pathology in diverse populations.
Why It Matters: This study challenges previous assumptions about the protective effects of a traditional lifestyle against dementia onset, highlighting the complex interplay of genetics, lifestyle, and environment in neurodegenerative disease risk, and adding rare incidence data for Indigenous populations.
Three years ago, researchers made a striking discovery: the Tsimané and Mosetén peoples of lowland Bolivia exhibited a remarkably low prevalence of dementia—a phenomenon attributed to a healthy low-fat diet, intense physical activity, and active social engagement.
“We hypothesize that energy gain from food intake was positively associated with late-life brain health in the physically active, food-limited world of our ancestors, but that obesity and other manifestations of a Western lifestyle now lead to greater cognitive aging and dementia in middle and older ages,” UC Santa Barbara anthropologist Michael Gurven said in 2023. When researchers evaluated their brains and cardiovascular systems using advanced imaging, the participants—who maintain largely nonindustrial forager-horticulturalist lifestyles—showed less brain atrophy and better cardiovascular health than industrialized populations in Europe and the United States.
However, a newly published longitudinal study adds nuance to the narrative. Appearing in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, the study revealed that the incidence of dementia in this Indigenous community is not dramatically different from that observed in US or Northern European populations, meaning that older adults developed dementia at rates comparable to those of their Western, industrialized counterparts.
“The surprising finding was that there weren’t big differences in dementia incidence,” said lead author Margaret Gatz, a professor of psychology and gerontology at USC and a senior scientist at the USC Center for Economic and Social Research. “That challenges us to identify the risk factors for developing dementia in the Tsimané population.”
Prevalence versus Incidence
In epidemiology, two primary metrics describe the occurrence of a disease within a population: “incidence” tracks new cases arising over a specified period, whereas “prevalence” captures the total proportion of existing cases at a single point in time.
The study followed 730 adults who were free of dementia at baseline and reassessed approximately five years later. Researchers identified 22 incident dementia cases, corresponding to an overall incidence rate of 7.40 cases per 1,000 person-years—a figure comparable to Western cohorts. During follow-up assessments, the prevalence remained below 2 percent, consistent with the team’s findings from three years prior and notably lower than rates documented in Western populations.
“Essentially, new cases among these Indigenous populations may appear at similar rates as those observed elsewhere, but the total number of cases at any point in time remains low,” explained Gurven, cofounder and codirector of the Tsimane Health and Life History Project. He posed the logical question: What is happening to individuals with dementia?
“One of the reasons for the low prevalence is that they don’t live very long with dementia,” Gurven said.
According to the authors, the community’s subsistence lifestyle provides critical context. As forager-horticulturalists living in an environment with constrained food availability, subsistence labor occupies much of daily life, and food insecurity remains widespread. “If dementia prevents a person from contributing to food production, it can become a burden on the family, with the older person’s decreasing nutritional status contributing to death,” the researchers noted. This dynamic, compounded by minimal access to medical infrastructure, comorbid conditions, and “insufficient family capacity to provide care may contribute to shortened survival.”
“Under their traditional lifeways, the risk of Alzheimer’s disease and related dementia is low,” Gurven said, “but it may not be as low as we originally thought. A longitudinal study like our new one is critical to get a better picture of disease risk.”
Funding: The National Science Foundation and the National Institutes of Health funded the work in part.
Published in journal: Alzheimer’s & Dementia: Journal of the Alzheimer’s Association
Title: Incidence of dementia and mild cognitive impairment in two Indigenous Bolivian cohorts
Authors: Margaret Gatz, Wendy J. Mack, Daniel Eid Rodriguez, Raul Quispe Gutierrez, Jesus Bani Cuata, Helena C. Chui, Ellen E. Walters, Daniel K. Cummings, Paul L. Hooper, Henrik Zetterberg, Caleb E. Finch, Benjamin C. Trumble, Jonathan Stieglitz, Michael D. Gurven, Randall C. Thompson, Gregory S. Thomas, The HORUS Team, Tsimane Health and Life History Project, and Hillard S. Kaplan
Source/Credit: University of California, Santa Barbara | Sonia Fernandez
Edited by: Scientific Frontline
Reference Number: epi092226_01