Endocrine Abstracts

Background: Environmental rhythmicity seems able to affect the hypothalamic-pituitary-gonadal axis in animals to achieve reproductive advantages. However, conflicting results were obtained when assessing the environmental-dependent rhythmicity on reproductive hormone secretion in humans.

Aim of the study: This study was designed to evaluate seasonal fluctuations of the main hormones involved in the hypothalamic-pituitary-gonadal axis in men, using a big data approach.

Methods: An observational, retrospective, big data trial was carried out, including all testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) measurements performed in a single laboratory between January 2010 and January 2019, using chemiluminescent microparticle immunoassay. Subjects presenting any known factor interfering with the hypothalamic-pituitary-gonadal axis were excluded from the analyses. However, according to the big data approach, no information about subjects’ clinical history was available, but only the diagnostic reason for biochemical examinations. The trend and seasonal distributions were analysed using autoregressive integrated moving average (ARIMA) models.

Results: A total of 12.033 data, accounting for 7.491 men (mean age 47.46 ± 13.51 years, range 18–91 years), were included. Mean testosterone serum levels (5.34 ± 2.06 ng/dl, range 1.70–15.80 ng/dl) showed a seasonal distribution with higher levels in summer (P = 0.008). A direct relationship between testosterone levels and maximum, minimum and mean temperatures (Rho:0.019, P = 0.041; Rho:0.023, P = 0.011; Rho:0.021, P = 0.024, respectively) and daylight duration (Rho:0.021, P = 0.020) was highlighted. LH (mean 4.64 ± 2.54 IU/l, range 1.00–15.00 IU/l) presented two peaks of secretion in autumn and spring (P = 0.001 and P = 0.001, respectively), independently from environmental parameters. No seasonal distribution was observed considering FSH serum levels (mean 5.51 ± 3.24 IU/l).

Conclusions: A clear seasonal fluctuation of both LH and testosterone was demonstrated in a large cohort of adult men, although a circannual seasonality of hypothalamic-pituitary-gonadal hormones in humans could be not strictly evolutionarily required. Testosterone seasonality seems independent from LH fluctuations, which could be regulated by cyclic central genes expression, and more sensible to environmental temperatures and daylight duration.