Yawning is linked to a person's age, reveals new study.
According to scientists, contagious yawning is linked more closely to a person's age than their ability to empathise, as previously thought. It also showed a stronger link to age than tiredness or energy levels, a BBC report said.
The study, involving 328 participants and led by Elizabeth Cirulli, assistant professor of medicine at Duke University in Durham, North Carolina, US has been published in the journal Plos One.
Researchers are now looking at whether the ability to catch yawns from other people is inherited, with the hope of helping treat mental health disorders.
Autism and schizophrenia sufferers are reportedly less able to catch yawns, researchers said, so understanding the genes that might code for contagious yawning could illuminate new pathways for treatment.
"This is the first study to look at a whole bunch of factors. It is the largest study, in terms of the number of people involved, to date," she said, adding that she did not know why contagious yawning decreased with age.
She added that although age was the most important predictor of contagious yawning, only 8 percent of the variation in whether or not a participant yawned was explained by their age. "The vast majority of variation in the contagious yawning response was just not explained."
The study used questionnaires to test the participants' empathy, levels of tiredness and sleep patterns.
During the study, 328 participants were shown a three-minute video showing other people yawning. Each subject had to click a button every time they yawned.
Overall, 68 percent of the participants yawned. Of those, 82 percent of people aged under 25 yawned, compared with 60 percent of people aged between 25 and 49, and 41 percent of people aged over 50.
Robert R Provine, professor of psychology at the University of Maryland, said the study was "unique" as it marked the first time a link between ageing and contagious yawning had been shown.
He said the study would "help to get down to the neurological nitty-gritty of contagious behaviours" and mental health disorders such as autism and schizophrenia.
Provine said the findings could also help to understand why laughing and coughing were so contagious.