Key result
High altitude exposure >5000 m significantly increased resting morning cortisol (14.5 vs 3.5 nmol/l, p=0.002) and post-exercise cortisol (9.2 vs 4.2 nmol/l, p<0.001) compared to 4270 m.
Why the study?
How does hypobaric hypoxia during ascent to > 5000 m affect resting and post-exercise salivary cortisol levels?
Cohort
How does hypobaric hypoxia during ascent to > 5000 m affect resting and post-exercise salivary cortisol levels?
Absolute Event Rate: 14.5% vs 3.5%
p-value: p=0.002
High altitude exposure to > 5000 m elevates resting morning cortisol, but the cortisol response to trekking appears suppressed at 4270 m before rising at higher altitudes.
Suppressed post-trek cortisol at 4270 m may affect fluid balance in trekkers; leaves open mechanisms and AMS relevance pending prospective data.
High altitude exposure normally leads to a marked natriuresis and diuresis. Acute mountain sickness is often associated with fluid retention, to which an elevated cortisol may contribute. Most investigators report a rise in resting cortisol with ascent, but little data exist regarding the cortisol response to a day trekking. We therefore measured salivary cortisol during ascent to > 5000 m in a cohort of between 42-45 subjects following a 6-h trek (samples taken between 15:30-16:30 h) and between 15-20 subjects at rest (morning samples taken between 08:00-09:00 h). Morning resting cortisol [nmol/l, mean±sd, (range)] was 5.5±2.9 (2.13-13.61) at 1300 m; 4.7±6.8 (1.4-27.02) at 3400 m, and significantly (p=0.002) rose between 4270 m [3.5±2.1 (1.4-8.34)] and 5150 m [14.5±30.3 (1.9-123.1)]. Post-exercise cortisol [nmol/l, mean±sd, (range)] dropped between 3400 m [7±6 (1.5-33.3)] and 4270 m [4.2±4.8 (1.4-29.5)] (p=0.001) followed by a significant rise in post-exercise cortisol between 4270 m [4.2±4.8 (1.4-29.5)] and 5 150 m [9.2±10.2 (1.4-61.3)] (p<0.001). There were no significant associations between severity of acute mountain sickness and cortisol levels. There was a significant though weak correlation between cortisol post-exercise at 5150 m and oxygen saturation at 5150 m (rho= - 0.451, p=0.004). In conclusion, this is the largest cohort to have their resting and post-exercise cortisol levels ascertained at high altitude. We confirm the previous findings of an elevated resting morning cortisol at > 5000 m, but present the novel finding that the cortisol response to a day trekking at HA appears suppressed at 4270 m.
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Woods et al. (2012) conducted a cohort in High altitude exposure. High altitude exposure and trekking vs. Lower altitudes (1300 m, 3400 m, 4270 m) was evaluated on Morning resting salivary cortisol levels (p=0.002). High altitude exposure >5000 m significantly increased resting morning cortisol (14.5 vs 3.5 nmol/l, p=0.002) and post-exercise cortisol (9.2 vs 4.2 nmol/l, p<0.001) compared to 4270 m.
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