The effects of physical exercise at high altitude on adrenocortical function in humans

The combined effects of sustained physical activity and hypoxia on adrenocortical function were investigated in 14 healthy volunteers, 8 males and 6 females (mean age 40.9 +/- 3.3 years), during a scientific expedition in the Himalayas. Plasma cortisol levels were measured in all subjects in basal conditions and after the administration of 1 mg dexamethasone (DXM) p.o. The study was performed before and after 15 days of intense trekking (Leh, altitude 3700 m). While on both occasions subjects retained their cortisol circadian fluctuations, basal and post-DXM cortisol levels at high altitude were significantly higher (p < 0.005 and p < 0.0005) than before climbing. Cortisol suppression was noted in all cases at low altitude, whereas 4 out of the 14 subjects did not show reduced hormone levels after 15 days of trekking. Moreover, nonsuppressor subjects had significantly higher (p < 0.05) baseline cortisol levels than suppressors. Basal and post-DXM hormone levels were found to be unrelated to age and sex of subjects. The present data further suggest that sustained physical activity at altitude activates adrenocortical function in normal individuals; however, in 30% of subjects DXM-induced cortisol suppression does not occur. To explain the latter observation, the concomitant role of hypoxia (and/or other environmental changes) and the subjective perception of physical stressors should be taken into account.