Sleep deprivation reduces aggression, testosterone in men

By Mark Cowen, Senior medwireNews Reporter

Sleep deprivation is associated with a reduction in reactive aggression and testosterone levels in men, Canadian study findings show.

Kimberly Cote and colleagues from Brock University in St Catharines, Ontario, found that testosterone levels in men decreased by 27% following 33 hours of sleep loss.

This is "a substantially greater reduction than the 10-15% decrease recently reported in a sleep restricted sample and the 1-2% decreases per year that are seen with age," say the researchers.

"Given that many people are chronically sleep deprived in modern society due to lifestyle, sleep disorders, and shift work, long-term reductions in testosterone may have a significant impact on men's sexual behaviour and reproduction, as well as general health," they add.

The findings come from a study of 49 men and women who were aged between 18 and 30 years.

The participants were randomly assigned to 33 hours of sleep deprivation (n=24) or no sleep deprivation (control group). Salivary testosterone, estradiol, and cortisol levels were assessed before and after sleep deprivation. Participants in both groups were also assessed for reactive aggression using the Point Subtraction Aggression Paradigm (PSAP) task.

The team found that men in the sleep deprivation group (n=11) showed a 27% reduction in testosterone levels after sleep deprivation compared with beforehand. By contrast, men in the control group (n=13) showed a 3% increase in testosterone levels over the same period.

Furthermore, although men in both groups showed a similar level of aggression before provocation on the PSAP task, men in the sleep deprivation group showed significantly lower levels of aggression after provocation than those in the control group.

There were no significant associations between sleep deprivation and cortisol levels in men or women. There were also no significant associations between sleep deprivation and aggression or estradiol levels in women.

"This is the first experimental study to demonstrate that sleep deprivation lowers reactive aggression in men," comment Cote and colleagues in Biological Psychology.

They add: "Both low testosterone and short sleep duration have been linked to increased mortality, and thus further research is needed to explore the relationship between testosterone and sleep and the impact on health."

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