Stress hormone opposes testosterone’s effects

A new study by the University of Texas at Austin has revealed that high levels of the stress hormone cortisol play a critical role in blocking testosterone's influence on competition and domination.

The findings show that when cortisol—a hormone released in the body in response to threat—increases, the body is mobilized to escape danger, rather than respond to any influence that testosterone is having on behaviour.

"It makes good adaptive sense that testosterone's behavioural influence during an emergency situation gets blocked because engaging in behaviours that are encouraged by testosterone, such as mating, competition and aggression, during an imminent survival situation could be fatal," said Robert Josephs, professor of psychology.

"On the other hand, fight or flight behaviours encouraged by cortisol become more likely during an emergency situation when cortisol levels are high. Thus, it makes sense that the hormonal axes that regulate testosterone levels and cortisol levels are antagonistic," he added.

The researchers suggest these findings reveal new insights into the physiological effects of stress and how they may play a role in fertility problems.

They indicate that high cortisol levels can affect libido by inhibiting testosterone production and in women, can produce severe fertility problems and result in an abnormal menstrual cycle.

"However, these effects of cortisol in both men and women are reversed when stress levels go down," Josephs said.

The findings are available online in Hormones and Behaviour.