Circulating sex hormones, specifically estrogen in females and testosterone in males, are associated with ambient environmental temperature during prolonged physical training.

Circulating sex hormones play important roles in reproductive and non-reproductive physiological homeostasis. We evaluated the relationships of sex hormones measured in urine and serum with ambient temperature (maximum and average daily temperatures) in male and female soldiers undergoing initial military training (n = 237, 125F; data are mean ± SD; age: 21 ± 4 years, BMI: 24 ± 3, body fat: 28 ± 7%). Participants provided intermittent blood samples for assessment of 17β-estradiol, total and free-testosterone, luteinizing hormone (LH), and sex hormone binding globulin. Females not using hormonal contraceptives (non-HC users) additionally provided daily first morning urine samples which were analyzed for metabolites of estrogen normalized to creatinine (estrone conjugates, E1C) and progesterone (pregnanediol glucuronide, PDG), LH, and follicle stimulating hormone (FSH). Linear mixed effects models were used to evaluate the relationship between maximum and average daily temperatures and circulating hormonal and gonadotropin concentrations. In urine collected from female non-HC users, maximum daily temperature was inversely associated with E1C and FSH (p = 0.0019, p < 0.001, respectively). Total testosterone was inversely related to maximum daily temperature in males (p < 0.001) and positively associated in both groups of females (non-HC users: p = 0.004, HC users: p = 0.018). Estradiol was inversely related to maximum daily temperature in female non-HC users only (p = 0.001). There was no relationship between temperature (maximum or average) and serum or urine LH, or urine PDG. These findings suggest that ambient temperature is associated with modest sex- and hormone-specific variation in circulating sex hormone concentrations during prolonged physical training.