Hillard Kaplan, Chapman UniversityFollow
Paul L. Hooper, Chapman University
Margaret Gatz, University of Southern California
Wendy J. Mack, University of Southern California
E. Meng Law, University of Southern California
Helena C. Chui, University of Southern California
M. Linda Sutherland, MemorialCare Health Systems
James D. Sutherland, MemorialCare Health Systems
Christopher J. Rowan, Renown Institute for Heart and Vascular Health
L. Samuel Wann, University of New Mexico
Adel H. Allam, Al-Azhar University, Egypt
Randall C. Thompson, University of Missouri - Kansas City
David E. Michalik, University of California, Irvine
Guido Lombardi, Universidad Peruana Cayetano Heredia
Michael I. Miyamoto, Providence Mission Hospital
Daniel Eid Rodriguez, San Simon University
Juan Copajira Adrian, Tsimane Health and Life History Project
Raul Quispe Gutierrez, Tsimane Health and Life History Project
Bret A. Beheim, Max Plank Institute of Evolutionary Anthropology
Daniel K. Cummings, Chapman University
Edmond Seabright, University of New MexicoFollow
Sarah Alami, Universite Mohammed 6 Polytechnic
Angela R. Garcia, Phoenix Children’s Hospital
Kenneth Buetow, Arizona State University
Gregory S. Thomas, MemorialCare Health Systems
Caleb E. Finch, University of Southern California
Jonathan Stieglitz, Institute for Advanced Study in ToulouseFollow
Benjamin C. Trumble, Arizona State UniversityFollow
Michael D. Gurven, University of California, Santa BarbaraFollow
Andrei Irimia, University of Southern California

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Little is known about brain aging or dementia in nonindustrialized environments that are similar to how humans lived throughout evolutionary history. This paper examines brain volume (BV) in middle and old age among two indigenous South American populations, the Tsimane and Moseten, whose lifestyles and environments diverge from those in high-income nations. With a sample of 1,165 individuals aged 40 to 94, we analyze population differences in cross-sectional rates of decline in BV with age. We also assess the relationships of BV with energy biomarkers and arterial disease and compare them against findings in industrialized contexts. The analyses test three hypotheses derived from an evolutionary model of brain health, which we call the embarrassment of riches (EOR). The model hypothesizes that food energy was positively associated with late life BV in the physically active, food-limited past, but excess body mass and adiposity are now associated with reduced BV in industrialized societies in middle and older ages. We find that the relationship of BV with both non-HDL cholesterol and body mass index is curvilinear, positive from the lowest values to 1.4 to 1.6 SDs above the mean, and negative from that value to the highest values. The more acculturated Moseten exhibit a steeper decrease in BV with age than Tsimane, but still shallower than US and European populations. Lastly, aortic arteriosclerosis is associated with lower BV. Complemented by findings from the United States and Europe, our results are consistent with the EOR model, with implications for interventions to improve brain health.


This article was originally published in PNAS, volume 120, issue 13, in 2023.

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This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.