Our results show that there may already be differences between men and women's ability to deal with stress even before birth

Dr Dino Giussani, University of Cambridge

Scientists examined levels of the hormone in unborn lambs and found that males released twice as much cortisol as females.

They believe the findings, presented to the Society for Endocrinology's annual meeting, can also be applied to humans and may explain why the two sexes respond differently to stress.

"We have known for a long time that men and women respond differently to stressful conditions," said Dr Dino Giussani, who led the study.

"It has been thought that this was down to environmental factors but we have shown that these differences between men and women may be pre-determined from birth."

Significant differences

The study on unborn lambs found little variation between males and identified a significant difference compared with females.

"The males released twice as much cortisol and there was little variation between them," Dr Giussani told BBC News Online. "This is a new idea, which may have direct clinical and agricultural implications.

"However, this work also suggests that males may be more predisposed than females to overreact to stressful conditions later in life."

He added: "Our results show that there may already be differences between men and women's ability to deal with stress even before birth."

Dr Giussani said his research team would now look at continuing the study on human foetuses.

A recent study suggested that every day around 270,000 people take time off work for stress-related illness. Absenteeism is estimated to have cost the UK �10.2bn last year.