AsianScientist (Feb. 20, 2026) –People who climb to high altitudes often experience headaches, a primary symptom of acute mountain sickness (AMS). While AMS and its associated headaches are thought to result from hypoxia, i.e., reduced oxygen delivery to body tissues, the underlying mechanisms, particularly the role of regional cerebral blood flow, are not well understood.
Previous studies on AMS have been conducted, but few have lasted long enough or taken place in real high-altitude environments.
To address this gap, a team from the Osaka Metropolitan University Research Centre for Urban Health and Sports measured blood flow and vessel diameter in the internal carotid and vertebral arteries of eight healthy men at the summit of Mount Fuji, 3,776 metres above sea level.
The study was conducted over three days, during which the team simultaneously recorded symptoms of altitude sickness, including headaches and fatigue. The results were published in the Journal of Applied Physiology.
Eight healthy men aged 22 to 46 years were recruited for the study. All participants were non-smokers and free from cardiovascular, metabolic, or neurological disease, as well as migraines and substance dependence. The participants were physically active but not engaged in formal training programmes and had not been at altitudes above 1,500 metres in the previous six months. Ultrasound screening confirmed the absence of vascular abnormalities.
Participants were instructed to avoid alcohol and strenuous physical activity for at least 24 hours before testing and to refrain from consuming caffeine for 12 hours beforehand. They were encouraged to drink more than two litres of fluid daily, although hydration and sleep were not formally monitored.
The study was conducted at the summit of Mount Fuji, a popular climbing destination that attracts more than 250,000 visitors each summer. As a result, AMS is a significant concern. Measurements were taken at low altitude (450 m) and on three consecutive days at the summit.
On the day of ascent, participants travelled by vehicle to a base camp at 1,280 meters, then reached the summit within three hours by bulldozer, arriving around 9:00 a.m. All measurements were performed between 1:30 p.m. and 5:30 p.m., at least two hours after a light meal, to minimise the effects of digestion on cerebral blood flow.
During each session, participants rested in a supine position for 30 minutes before data collection began, which lasted 20 minutes in the same position. They were asked to breathe normally and remain silent. Symptoms of AMS were recorded before each measurement. After spending three nights at the summit, participants descended on foot and returned to low altitude.
Ambient pressure, temperature, and humidity were monitored at each site throughout the study.
Results showed that blood flow and vessel diameter in the internal carotid artery increased with longer high-altitude exposure, while vertebral artery flow rose on the first day and then declined. Headache severity increased at altitude and was closely linked to changes in carotid artery diameter and vertebral artery flow and velocity.
Although overall AMS symptoms also increased, they were largely unrelated to blood flow measures, except for vertebral artery velocity. The findings suggest that increased regional cerebral blood flow, particularly in the carotid and vertebral arteries, may drive high-altitude headaches and contribute to AMS.
“These findings shed light on one mechanism behind altitude sickness onset and can possibly aid in managing climbers’ physical conditions during mountain hikes and high-altitude training,” said Kazunobu Okazaki, director, Research Centre for Urban Health and Sports, Osaka Metropolitan University.
“We believe that further investigation into individual differences, gender differences, and the acclimatization process during long-term stays will yield insights applicable to the prevention and early management of altitude sickness. In addition, the relationship between cerebral blood flow and headaches may also contribute to understanding other headache disorders, such as migraines,” he added.
Source: Osaka Metropolitan University ; Image: Tomasvi/Freepik
The study can be found at Effect of short-term high-altitude acclimatization on the relationship between cerebral blood flow and symptoms of mild acute mountain sickness in males
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.
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