People traveling to or living at higher elevations often notice a distinct decline in their quality of sleep. This common experience of fragmented or unrefreshing rest is a direct consequence of the body’s physiological response to the change in atmospheric conditions. Noticeable sleep disruption frequently begins at elevations around 8,000 feet (about 2,500 meters) and becomes more pronounced with further ascent. Travelers commonly report difficulty falling asleep, frequent awakenings, and feeling generally unrefreshed.
The Physiological Cause: Hypoxia and Reduced Oxygen Intake
The fundamental reason for altered sleep at elevation is the phenomenon of hypobaric hypoxia. As elevation increases, the atmospheric pressure steadily decreases. Although the air still contains the same percentage of oxygen (approximately 21%), the lower barometric pressure results in a reduced partial pressure of oxygen. This translates directly to fewer oxygen molecules being available for the lungs to transfer into the bloodstream, leading to oxygen deprivation, or hypoxia, in the body’s tissues.
In response to this lack of oxygen, the body attempts to compensate by increasing the rate and depth of breathing, a process called hyperventilation. This stimulated ventilation helps raise the amount of oxygen in the blood, but it also causes a reduction in carbon dioxide levels. The drop in carbon dioxide is particularly disruptive during sleep because carbon dioxide is the primary chemical stimulus that regulates breathing. When carbon dioxide levels fall too low, the brain’s respiratory center temporarily reduces the drive to breathe, which can lead to unstable breathing patterns during the night.
How Elevation Alters Sleep Architecture
The primary and most disruptive change to sleep structure at elevation is the onset of high-altitude periodic breathing. This is a pattern where periods of rapid, deep breathing alternate with temporary cessations of breath, known as central apneas. The hyperventilation driven by low oxygen causes carbon dioxide levels to drop, which then signals the brain to stop breathing until oxygen levels fall low enough to restart the cycle.
These cycles of periodic breathing can occur frequently and lead to numerous brief awakenings, fragmenting sleep and making it feel unrefreshing. Studies show that total sleep time and overall sleep efficiency are reduced at elevation. The architecture of non-rapid eye movement (NREM) sleep is also significantly affected, with a notable decrease in deep, slow-wave sleep (stages N3 and N4). The time spent in lighter sleep stages, particularly Stage 1 NREM, increases, contributing to the feeling of poor sleep quality. Rapid Eye Movement (REM) sleep is variably affected, with some research indicating a reduction. The overall result is a night of highly fragmented rest.
The Process of Acclimation
The human body is capable of adapting to the reduced oxygen environment through a process called acclimatization, which gradually improves sleep quality. This adaptation involves several physiological adjustments aimed at restoring oxygen balance. The initial and most immediate adjustment is the sustained increase in ventilation, which helps to maintain a higher level of oxygen in the blood. A longer-term change involves the kidneys increasing the excretion of bicarbonate, a process that helps to normalize the blood’s pH balance, which was altered by the initial hyperventilation.
This chemical buffering allows the respiratory drive to remain active even when carbon dioxide levels are low, stabilizing the breathing pattern over time. The production of red blood cells also begins to increase, improving the blood’s capacity to transport oxygen. For most people, a noticeable improvement in sleep and a reduction in periodic breathing occur over several days. Full acclimatization can take between one to three days for every 1,000 meters (3,300 feet) gained above 2,500 meters (8,200 feet).
Practical Strategies for Improving Sleep
The most effective non-prescription strategy for mitigating sleep disturbance at elevation is to plan a gradual ascent. Traveling slowly allows the body more time for natural acclimatization, minimizing the severity of hypoxia and the resulting sleep issues. A common recommendation is to avoid increasing your sleeping altitude by more than 1,600 feet (500 meters) per day once above 9,800 feet (3,000 meters) and to schedule a rest day every few days.
Lifestyle Adjustments
- Maintain consistent hydration by drinking plenty of water, as the dry air at elevation can lead to dehydration, which may worsen symptoms.
- Avoid alcohol and sedatives, including many common sleeping pills, because they can suppress the body’s natural respiratory drive, potentially worsening nocturnal oxygen levels and periodic breathing.
- Practice deep breathing exercises to help enhance oxygen intake before and during sleep.
Medical Intervention
A prescription medication called acetazolamide (Diamox) is often recommended to accelerate acclimatization. This drug works by inducing a mild metabolic acidosis, which acts as a respiratory stimulant, encouraging faster breathing. By stimulating ventilation, acetazolamide is effective at reducing the severity of periodic breathing and improving nocturnal oxygenation. When taken for prevention, a dose of 125 mg twice daily, starting the day before ascent, is commonly used.