Cortisol may be to blame for aggression among 10-year-old boys

The hormone cortisol has been linked to increased aggressive behaviour in 10-year-old boys, Spanish researchers say.
Scientists studied the relationship between hormones and aggressive behaviour in girls and boys between the ages of eight and ten.
The subjects who experienced the greatest increase in levels of aggression by ten years of age were those whose cortisol levels had also increased during those two years.
Researchers, including Eider Pascual-Sagastizabal from The University of the Basque Country, measured the levels of three steroid hormones: testosterone, estradiol and cortisol.
The results demonstrated that there was indeed a change in the levels of aggressive behaviour.

"This only occurred in boys: at ten years of age they were more aggressive than at eight years of age. The girls, nevertheless, did not experience any changes to their levels of aggression during these two years," Pascual-Sagastizabal said.

The experts analysed whether changes in any of the hormones that were measured were associated with the change in aggressive behaviour that occurred between these two ages.
They discovered that the subjects whose levels of aggression had increased most by the age of ten were those whose levels of cortisol had also increased over the two years.
On the contrary, the boys whose levels of aggression had decreased most between eight and ten years of age were the ones whose levels of estradiol had increased most between the two ages.

"These results appear to indicate that hormones have a different effect on aggressive behaviour depending on the type of hormone: cortisol and estradiol.
"A greater increase in cortisol is linked to a greater increase in levels of aggressive behaviour, while a greater increase in estradiol corresponds to a decrease in levels of aggressive behaviour," said Pascual-Sagastizabal.
Researchers concluded that the study may aid in a greater understanding of the biological mechanisms underlying aggression by providing further information on the different effects that hormones can have on aggressive behaviour in school-aged children depending on the type of hormone and the sex of the child.

The study was published in the American Journal of Human Biology.