US scientists believe hearing your mother's voice on the telephone has same stress-busting effect as a cuddle

Children know that mum's got the words when life seems to be getting too much.

Now it seems her voice on the phone can work the same soothing magic as when she is there to give her offspring a comforting cuddle. US scientists believe hearing mother down the line produces the same stress-busting effect on her daughter as physical contact such as a hug or a loving arm round the shoulder.

In a study that will send phone companies into their own comfort zone, researchers found mothers' calls released similar levels of the social bonding hormone oxytocin in girls as when they were in close proximity. Writing in the journal Proceedings of the Royal Society B, the scientists report how they deliberately raised the stress levels of 61 girls aged seven to 12. The children had to make an impromptu speech and solve maths problems in front of strangers. This sent their hearts racing and levels of stress hormone cortisol higher.

The girls were then divided into three groups, one comforted by physical contact with their mothers, another by phone calls from their mothers and a third by watching a film deemed emotionally neutral, the March of the Penguins.

Oxytocin rose to similar levels in the first two groups and did not increase in the third, saliva and urine tests revealed. As this hormone's presence grew, cortisol faded.

Leslie Seltzer, from the University of Wisconsin-Madison, who led the research, said: "The children who got to interact with their mothers had virtually the same hormonal response, whether they interacted in person or over the phone.

"It was understood that oxytocin release in the context of social bonding usually required physical contact. But it's clear from these results that a mother's voice can have the same effect as a hug, even if they're not standing there."

The effects lingered too, said another member of the team. "It stays well beyond the stressful task," said Professor Seth Pollak, from the university's child emotion laboratory. "By the time the children go home they're still enjoying the benefits of this relief and their cortisol levels are still low. That a simple telephone call could have this physiological effect on oxytocin is really exciting."

Girls were used in the study because oxytocin responses are stronger in females than in males. In adult women the hormone plays a role in labour, preparing for birth and breastfeeding.

There might be an evolutionary reason for other responses, experts believe. A threatened male is free to choose between "fight or flight", but this may not be so easy for a female who is pregnant or caring for offspring. It might be that females alleviate stress by making the peace.

Seltzer is investigating whether other forms of communication, such as text messaging, have an effect on oxytocin and hopes to expand the research into animals.

"Lots of very social species vocalise," she said. "On the one hand we're curious to see if this effect is unique to humans. On the other we're hoping researchers who study vocal communication will consider looking at oxytocin release in other animals and applying it to broader questions of social behaviour and evolutionary biology."