A study, presented at a British Psychological Society conference in Leeds, compared 25 men with fertility problems with 25 with none.

It suggested that "new men", who find it easier to talk about their feelings, could be more likely to be fertile.

Although the 25 fertile men reported more stress-causing incidents day to day over a two-week period, they were far more likely to talk about them.

The report's author, psychologist Keith Hurst, said that bottling up stressful events was far more likely to lead to higher stress level overall.

And increased stress could well lead to reductions in the body's ability to cause stress, he said.

He said: "There is a wealth of psychological literature saying that it tends to be the day to day things that have an impact on our psychological wellbeing and physical health."

Traffic jam reactions

"These are the straws that break the camel's back", he said.

Men who are good at expressing their feelings might include someone, who, sitting in a traffic jam, would talk to their passenger about how frustrated they were feeling.

"The fertile men were 'cartharsis coping', anything from just talking about things to getting quite upset or angry," said Keith Hurst.

He is now planning more research to hopefully prove the physical link between stress and fertility.

Male fertility is known to be on the decline in many Western industrialised countries, although it is not known why.

It is thought that the stress hormone cortisol, or more particularly another chemical, CRH, also produced by the body, can interfere directly with sperm production.