Background
Approximately 81.6 million individuals reside permanently at altitudes above 2,500 meters, with many more intermittently exposed to high-altitude environments through travel, work, or recreation. Hypoxia, a reduction in available oxygen, can adversely affect human physiology and cognitive performance. While younger adults often exhibit resilience to moderate hypoxia[1], the extent to which middle-aged adults experience cognitive changes remains less established. Age-related declines in neurovascular coupling and cerebral autoregulation may increase susceptibility to hypoxia-induced impairments, underscoring the importance of focused research in this demographic.

Methods
Sixteen healthy participants (aged 45–65 years) were recruited to investigate the impact of acute normobaric hypoxia on cognitive performance and cerebral oxygenation. Each participant attended four separate sessions in a hypoxia chamber, simulating altitudes of 0 m (normoxia), 1,500 m (low altitude), 3,000 m (moderate altitude), and 4,500 m (high altitude). At each session, participants completed a cognitive test battery comprising the Stroop test, N-back task, Corsi block-tapping test, and a divided attention task. Cerebral oxygenation was assessed continuously using near-infrared spectroscopy (NIRS), measuring tissue saturation index (TSI), total hemoglobin (tHb), deoxyhemoglobin (HHb), and oxyhemoglobin (O2Hb). Changes in these parameters (ΔTSI%, ΔtHb, ΔHHb, and ΔO2Hb) were determined by subtracting normoxic resting values from those obtained during each hypoxia level. Perceived exertion was evaluated after each cognitive task using the DP15 rating scale.

Results

Exposure to graded hypoxia significantly impaired cognitive performance in middle-aged adults, particularly at moderate to high altitudes (3,000–4,500 m). Compared with normoxia, participants exhibited both slower reaction times and decreased accuracy on the Stroop test (p < 0.05), reduced accuracy on the N-back task (p < 0.05), as well as declines in reaction time and accuracy on the Corsi block-tapping (p < 0.05). These deficits were more pronounced under high-altitude conditions (4,500 m). Correlation analyses indicated a strong positive relationship between reduced oxygen availability (SpO2) and heightened perceived exertion (p < 0.05), suggesting that lower oxygen levels may directly contribute to cognitive performance decrements.

Conclusion

Acute normobaric hypoxia at simulated moderate to high altitudes significantly affects cognitive function in middle-aged adults, underlining a potential vulnerability in this demographic. These findings emphasize the importance of monitoring and mitigating hypoxia-related risks for individuals exposed to lower oxygen environments, and warrant further research into interventions that could preserve cognitive performance at altitude.

References

1. Ramírez-delaCruz M, Ortiz-Sánchez D, Bravo-Sánchez A, Portillo J, Esteban-García P, Abián-Vicén J. Effects of different exposures to normobaric hypoxia on cognitive performance in healthy young adults.: Normobaric hypoxia and cognitive performance. Physiology & Behavior. 2025;288:114747.