Sex Hormones May Modulate Thermoregulatory Responses to Heat Acclimation in Women

Introduction: Female sex hormones, specifically estradiol and progesterone, are known to have pronounced thermoregulatory effects. However, the potential impacts of these hormones on heat acclimation (HA) are unknown. Purpose: Investigate the impact of female sex hormone concentration on adaptation to heat stress. We hypothesized that the change in core temperature (Tcore) during a HA session would be related to the concentrations of sex hormones in the blood and urine. Methods: Sixteen women (mean ± SD; age: 24 ± 5 yr; ht: 162 ± 6 cm; wt: 68 ± 8 kg, 4 hormonal contraceptive users) participated in this investigation. Volunteers underwent 10-days of exercise heat stress (walking at 1.39m·s -1 , 2% grade, 40°C, 40% relative humidity, 1.34m·s -1 windspeed for 120 minutes). Tcore and heart rate (HR) were measured continuously. Blood samples were taken pre and post exercise on days 1 and 10 for evaluation of estradiol and progesterone, and urine samples were taken daily to evaluate estradiol, progesterone, estradiol metabolite estrone glucuronide (E1G), and progesterone metabolite pregnanediol glucuronide (PDG). The PDG:E1G ratio was also calculated. Linear mixed effects models were conducted to analyze the impact of female sex hormones and metabolites on thermoregulatory responses to HA on whole and across days. Results: There was no impact of serum estradiol or progesterone on Tcore or HR on any day (p>0.05). Marginal effects of urinary estradiol, progesterone, E1G, and PDG were significant only for HA day 1 (p<0.01). PDG:E1G had a significant marginal effect on days 7, 9, and 10 (p<0.05). There was a positive relationship between Tcore and PDG:E1G ratio when trials were pooled showing for every one unit increase in PDG:E1G there was a 1.1363 (0.54) °C increase in Tcore. There was no impact of sex hormones on HR. Conclusion: These results suggest that sex hormones may influence Tcore responses and thermoregulation during HA, but further research is required to elucidate the magnitude of the effect and if it varies over the time course of adaptation. Funded by USAMRDC: author views not representative of the U.S. Army or DoD. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.