New York, Nov 26 (IANS): Facebook use can both spike and regulate the levels of stress hormone cortisol in teenagers, finds a new study by researchers at University of Montreal, Canada.

Having more than 300 Facebook friends increased teenagers' levels of cortisol, the study found.

On the other hand, teenagers who act in ways that support their Facebook friends - for example, by liking what they posted or sending them words of encouragement - decreased their levels of cortisol, Techvibes.com reported.

"While other important external factors are also responsible, we estimated that the isolated effect of Facebook on cortisol was around eight percent,a said lead researcher professor Sonia Lupien.

Participants were asked about their frequency of use of Facebook, their number of friends on the social media site, their self-promoting behaviour, and finally, the supporting behaviour they displayed toward their friends.

Along with these four measures, the team collected cortisol samples of the participating adolescents.

"We were able to show that beyond 300 Facebook friends, adolescents showed higher cortisol levels," Lupien added.

None of the adolescents suffered from depression at the time of the study.

"We did not observe depression in our participants. However, adolescents who present high stress hormone levels do not become depressed immediately. It can occur later on," Lupien said.

The study was published in the journal Psychoneuroendocrinology.