Preserved circadian variation in cortisol and androgens during a ski traverse of Antarctica in summer.

Antarctic expeditions present extreme physiological challenges due to cold temperatures, high physical exertion, and 24-hour daylight. This observational study evaluated endocrine adaptation in nine participants (six men, three women) during a 47-day, 1,000 km unassisted ski traverse. Detailed salivary sampling was conducted before, during and after the expedition, corroborated by blood and hair sampling before and after the expedition. Cortisol, testosterone, and androstenedione were measured using mass spectrometry, and thyroid hormones via immunoassay. Diurnal cortisol, androstenedione and testosterone variation was preserved, while the morning cortisol increased during the expedition, suggesting that exercise demands overshadow the effects of continuous daylight in controlling hypothalamic-pituitary-adrenal and gonadal axis function. Morning testosterone decreased during the expedition, with a greater effect seen among men. No significant changes were seen in blood or hair steroid hormones. Gonadotropins in women indicated central suppression pre-expedition, normalizing post-expedition. Thyroid-stimulating hormone levels increased post-expedition without significant changes in free T3 or T4, consistent with mild polar T3 syndrome. These findings highlight the adaptability of hypothalamic-pituitary function to combined stressors of exercise, energy deficit, and cold. This is the first study to capture in situ endocrine responses during an Antarctic traverse, advancing our understanding of human adaptation in extreme environments.