Higher Prevalence of Cognitive Impairment in Residents of High-Altitude Regions

Introduction: A major health issue in individuals living at high-altitude regions is an increase in the number of red blood cells (RBCs). This condition generates a series of physiological alterations including the nervous system, where damage can occur due to increased blood viscosity. This increased viscosity, in turn, could compromise oxygen uptake, potentially linked to a degree of cognitive impairment. Objective: To determine the association between exposure to chronic hypoxia and sleep quality with the degree of cognitive impairment in a young adult population residing at different altitude levels. Methodology: A cross-sectional study was conducted with 200 apparently healthy subjects (aged 21–26 years) permanently residing in four Peruvian cities: Lima (154 m), Arequipa (2335 m), Puno (3820 m), and La Rinconada (5100 m) (n = 50 per location). Physiological profiles (SpO2, blood pressure, heart rate, hemoglobin, and hematocrit) were measured. Cognitive impairment and sleep quality were evaluated using the Montreal Cognitive Assessment (MoCA) and the Pittsburgh Sleep Quality Index (PSQI). Sex-stratified hierarchical multiple linear regression models with bootstrapping were utilized for independent correlation analysis. Results: Hemoglobin levels gradually increased with altitude, peaking at 19.47 ± 3.01 g/dL in La Rinconada, while SpO2 decreased to 81.64%. Moderate-to-severe cognitive impairment was exclusively restricted to the extreme altitude population of La Rinconada, where only 10% of subjects remained unaffected. In the sex-stratified multivariate regression, residency in La Rinconada initially served as a robust negative predictor of MoCA scores among women (β = −5.52, p < 0.001); however, this geographical effect lost statistical significance after adjusting for biological variables in Model 2 (β = −4.72, p = 0.178). In the fully adjusted models, neither individual hemoglobin levels nor SpO2 fluctuations displayed an independent linear association with cognitive performance in either sex (p > 0.05). Sleep quality was poor across cohorts but showed no significant association with cognitive impairment (p = 0.174). Conclusions: Chronic exposure to severe hypoxia (>5000 m) is associated with a greater presence of cognitive impairment, which is largely accounted for by individual physiological adaptations rather than isolated, linear effects of independent hematological or subjective sleep parameters.