The cortisol response to hypobaric hypoxia at rest and post-exercise.

Area of Science:

• Endocrinology
• Altitude Physiology
• Human Physiology

Background:

• High altitude exposure typically causes natriuresis and diuresis.
• Acute mountain sickness is linked to fluid retention, potentially influenced by elevated cortisol.
• Existing research shows increased resting cortisol with altitude, but limited data exists on cortisol responses during trekking.

Purpose of the Study:

• To measure salivary cortisol levels during ascent to over 5000m in a large cohort.
• To investigate the cortisol response to a 6-hour trek at high altitude.
• To explore associations between cortisol levels, acute mountain sickness, and oxygen saturation.

Main Methods:

• Salivary cortisol was measured in 42-45 subjects during ascent and in 15-20 subjects at rest.
• Samples were collected in the morning (resting) and afternoon (post-trek).
• Altitude levels included 1300m, 3400m, 4270m, and 5150m.

Main Results:

• Resting morning cortisol showed a significant rise between 4270m and 5150m (p=0.002).
• Post-exercise cortisol decreased from 3400m to 4270m (p=0.001) and then significantly increased from 4270m to 5150m (p<0.001).
• No significant link was found between acute mountain sickness severity and cortisol levels, but a weak correlation existed between post-exercise cortisol at 5150m and oxygen saturation (rho=-0.451, p=0.004).

Conclusions:

• This study confirms elevated resting morning cortisol at altitudes above 5000m.
• A novel finding is the suppressed cortisol response to trekking at 4270m.
• The cortisol response to high altitude trekking requires further investigation.