Physical activity mediates age differences in cognition among Tsimane forager-horticulturalists.

BACKGROUND The Tsimane and Moseten of the Bolivian Amazon are highly physically active and exhibit low rates of cognitive impairment and brain atrophy. METHODS We use structural equation modelling to examine how their physical activity levels mediate the relationship between a) age and cognition, and b) age and cognition via brain volume (BV). RESULTS Tsimane males (n = 305, mean ± SD age = 59.94 ± 9.68) and Tsimane females (n = 265, mean ± SD age = 59.28 ± 9.79) exhibit significantly higher levels of physical activity than Moseten males (n = 106, mean ± SD age = 58.15 ± 9.93) and Moseten females (n = 96, mean ± SD age = 56.63 ± 9.69). Physical activity significantly mediates the relationship between age and cognition in Tsimane males (indirect effect estimate β = -0.01, p < .01) and Tsimane females (indirect effect estimate β = -0.04, p = .01), but not in Moseten males or females. CONCLUSIONS Among Tsimane males, who are more physically active than Tsimane females, the association between age and cognition via BV is significantly mediated by physical activity. Among Tsimane females, mediation occurs directly via physical activity, bypassing BV. These results suggest that mechanisms of cognitive differences across ages differ by sex and population. Studying the relationship between brain atrophy and lifestyle in non-industrialized populations elucidates biological and environmental correlates of brain health.