Endocrine effects of repeated sauna bathing

Area of Science:

• Endocrinology
• Environmental Physiology
• Human Physiology

Background:

• Heat exposure, such as in Finnish saunas, can induce physiological stress.
• Hormonal responses to acute heat exposure require further investigation.

Purpose of the Study:

• To investigate the effects of controlled dry heat exposure on endocrine and neuroendocrine functions in healthy adults.
• To assess changes in pituitary and adrenal hormones, thyroid hormones, and catecholamines.

Main Methods:

• Healthy male and female volunteers underwent 7 days of dry heat exposure (80°C) for 1 hour twice daily.
• Plasma and serum hormone levels (ACTH, cortisol, TSH, thyroid hormones, testosterone, gonadotropins, prolactin, GH) were measured.
• Urinary catecholamine excretion was also determined at baseline and during the study period.

Main Results:

• No significant changes were observed in thyroid hormones, TSH, testosterone, FSH, or LH.
• Serum cortisol and plasma ACTH showed slight decreases, while urinary catecholamines increased slightly.
• Significant increases in serum GH (16-fold in males) and prolactin (2.3-fold in males, >4-fold in females) were observed.
• GH levels declined after day 3, but prolactin remained elevated in males.
• Elevated prolactin in females was associated with transient amenorrhea in some subjects.

Conclusions:

• Dry heat exposure significantly impacts GH and prolactin release, potentially mediated by dehydration.
• Hormonal responses, particularly prolactin, can be pronounced and prolonged.
• Further research is needed to elucidate the precise mechanisms and long-term implications of these heat-induced hormonal shifts.