A&D: Residents of Two Amazonian Indigenous Communities Showed Unusually Low Rates of Dementia

Two Indigenous communities in the Bolivian Amazon have been found to have unusually low rates of dementia. Over five years, fewer than 2% of older participants developed the condition, while dementia prevalence in the United States and Europe is three to four times higher. The findings were published in the journal Alzheimer’s & Dementia (A&D).

The researchers followed 730 adult residents of the Tsimane and Moseten communities who did not have dementia at the beginning of the study. Over five years, 22 participants were diagnosed with the condition. Some people died before the study ended, so the researchers also took the high mortality rate among older residents into account.

The Tsimane are a population of about 17,000 people who rely on hunting, fishing, and farming and lead physically active lives. The Moseten are genetically and linguistically related to the Tsimane but have greater access to stores, clean water, and medical care.

The authors believe that the low rate of dementia may be associated with lifestyle factors. Members of both groups have lower rates of certain risk factors for vascular disease, including obesity, hypertension, and diabetes. However, the study did not establish a direct link between these characteristics and protection against dementia.

Genetic risk factors were similar to those observed in developed countries. Older age and carrying the APOE ε4 gene variant increased the likelihood of developing dementia.

At the same time, the disease among Amazonian residents often differed from typical Alzheimer’s disease. Many patients showed signs of vascular disorders, strokes, and changes characteristic of Parkinson’s disease. Biomarker analysis also revealed evidence of neurodegeneration and inflammation.

The researchers note that the low prevalence of dementia cannot be explained by lifestyle alone: after receiving a diagnosis, participants’ life expectancy was two to three times shorter than in the United States, and their risk of death was more than six times higher than that of people without cognitive impairment.

In future studies, the researchers plan to determine how much of the unusually low risk of dementia can be attributed to diet, physical and social activity, genetics, and differences in immune system function.

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