Relationship between heart rate variability and the serum testosterone-to-cortisol ratio during military service

Abstract

The autonomic nervous system and circulating hormones control a stress reaction through a complex interaction. We tested the hypothesis that changes in cardiac vagal regulation may be positively associated with the serum testosterone-to-cortisol ratio during the first week of military service in 24 conscripts aged 19.0±0.3 years. Cardiac autonomic function was assessed by measuring high-frequency (HF: 0.15–0.4 Hz) and low-frequency (LF: 0.04–0.15 Hz) power spectral indices of R-R intervals during supine rest and during a controlled standing condition (5 min for both) from the second to the seventh mornings at the beginning of military service. Blood samples were collected to analyse the basal serum testosterone-to-cortisol ratio on the seventh morning. Changes in heart rate and high-frequency power measured in the standing condition were positively correlated with the serum testosterone-to-cortisol ratio at day 7 (r= − 0.42 and r=0.45, respectively; P<0.05 for both). However, changes in low-frequency power and LF/HF ratio did not correlate with testosterone or cortisol concentration. The present results suggest a relationship between changes in cardiac vagal regulation during a long-term mentally stressful condition and the serum testosterone-to-cortisol ratio. This association was more marked during the controlled standing condition.