Dementia Remains Uncommon Among Older Tsimane and Moseten Adults in Bolivia

Dementia remained uncommon among older adults in two Indigenous communities in the Bolivian Amazon, according to a 2026 follow-up study. Researchers found that about 7 people per 1,000 developed dementia each year, while roughly 2% were living with the condition at any one time.

The findings come from the Tsimane and Moseten peoples, whose communities obtain much of their food through farming, fishing, hunting and foraging. The groups were described as physically active and as having high-fiber, low-sugar diets, along with relatively low rates of high blood pressure, obesity and diabetes. They also face heavy infection burdens, limited medical care and frequent food insecurity.

What the follow-up found

The study invited everyone aged 60 and older in 89 Tsimane and 16 Moseten villages. Researchers assessed participants in three rounds: 2017–2019, 2020–2022 and 2023–2024. Follow-up participation was 97% in the second round and 91% in the third.

Among 730 adults who did not have dementia at the first assessment, 22 developed it over a median of 4.7 years. That corresponded to 7.40 cases per 1,000 person-years, with a 95% confidence interval of 4.87 to 11.24. Incidence was similar between the two populations: 7.36 per 1,000 person-years among Tsimane participants and 7.49 among Moseten participants.

Dementia prevalence was 1.18% at baseline, 2.00% in the second round and 1.91% in the third. Before about age 80, age-specific yearly risk was in the same general range as estimates from European and US studies, although each age band in the Tsimane analysis contained only a handful of cases.

Among Tsimane participants, yearly incidence rose from 1.48 per 1,000 at ages 65–69 to 20.28 per 1,000 at ages 75–79. The estimates had wide error bars. Incidence was 8.71 per 1,000 in men and 6.09 per 1,000 in women, a difference that was not statistically significant.

Low incidence did not mean low impact

People with dementia had a substantially higher risk of death than cognitively normal participants. After adjustment for age, sex and population, the hazard of death was 6.14 times higher among people with dementia. The corresponding hazard for people with mild cognitive impairment, or MCI, was 2.70 times higher than for people with normal cognition.

In the second study round, death rates were 620 per 1,000 person-years among people with dementia and 31 per 1,000 person-years among those with normal cognition. By the end of follow-up, all participants who had dementia at baseline had died, compared with 40% of those with MCI and 21% of those with normal cognition.

Relatives were interviewed for 98 of 108 deaths that occurred before the next visit. The reported causes most often included potentially treatable infections such as tuberculosis, kidney failure and accidents. Stroke was mentioned in 30% of dementia deaths.

The researchers estimated that survival with dementia was two to three times shorter than in the United States. This was an estimate rather than a direct survival measurement presented as the study’s primary summary result.

What the study suggests about risk factors

The analysis identified some possible associations but could not establish causes. APOE ε4, a genetic variant associated with dementia risk in other research, was present in 53% of genotyped dementia cases and 20% of people who remained dementia-free. Carriers had about five times the hazard of dementia in the study.

Thoracic aortic calcium scores above 500 were found in 73% of dementia cases and 35% of non-cases, and were associated with a hazard ratio of 3.29. By contrast, blood pressure, cholesterol and fasting glucose measured before baseline did not predict dementia, while inflammatory markers were not related to it.

Only 11 dementia cases had matching blood samples. In that small group, amyloid and tau markers did not distinguish participants with dementia from cognitively normal peers. Higher neurofilament light chain was associated with dementia, indicating general nerve damage but not identifying a specific cause.

Only five of the 22 new cases had a memory-led pattern resembling Alzheimer’s disease. The researchers’ view that vascular brain injury may contribute more to dementia than classic Alzheimer’s disease was explicitly described as speculative.

Why the results need careful interpretation

The study was observational and small, with only 22 new dementia cases. Its risk-factor analyses were exploratory, and age-specific estimates were based on few cases. The researchers could not directly test whether a subsistence lifestyle protects against dementia.

Assessing cognition was also challenging. Many participants had never attended school, so conventional reading and drawing tasks were replaced with activities such as copying a design with matchsticks. Scores were compared with local norms based on age, sex and literacy. Widespread uncorrected vision and hearing loss, uncertain ages and limited imaging added further difficulties, particularly when classifying MCI.

Two independent teams applied standard DSM-5 criteria for dementia and MCI. The same Bolivian physician examined participants in each round, and Tsimane participants were interviewed in their own language. Even so, fewer post-death interviews were available for people with MCI, meaning some later dementia cases may have gone uncounted.

Comparisons with Europe, the United States and other Indigenous populations should also be treated cautiously because the underlying studies used different methods. The researchers noted that the relatively small number of people in their 80s partly contributed to the lower overall incidence in the Bolivian communities.

A population in transition

The findings offer a picture of dementia in communities with a distinct combination of activity patterns, food systems, infection exposure and access to care. They do not show that any one lifestyle prevents dementia, nor do they establish that the communities’ diet or physical activity caused the observed rates.

The researchers expect dementia patterns may change as cell-phone coverage, motorized canoes and motorcycles bring more market foods and reduce physical work, while improved medical care extends survival. For readers, the broader relevance is that dementia rates reflect more than biology alone: living conditions, education, healthcare access, survival and how cognitive decline is measured can all shape the numbers reported.

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