Sperm become casualties of the road

Driving for long periods can cause more than frayed nerves. Scientists have found sitting behind the wheel can also result in falling sperm counts.

Driving for long periods can cause more than frayed nerves. Scientists have found sitting behind the wheel can also result in falling sperm counts.

The testicles of male drivers heat up enough to have an impact on sperm production, and researchers believe the findings explain why the wives of taxi and lorry drivers find it harder to conceive than the partners of casual drivers.

But the discovery that the scrotum can heat up by as much as 2C after a couple of hours behind a wheel is unlikely to account for the decline in sperm counts seen in Western men over the past half century.

Studies have shown sperm counts falling by 1.5 to 3 per cent a year. Tighter underwear or a more sedentary lifestyle is unlikely to account for such a large decrease, scientists believe.

A study led by Louis Bujan at the Male Fertility Research Group at Hÿpital La Grave in Toulouse showed scrotal temperatures rise significantly in male drivers, accounting for at least some of the loss of male fertility.

Previous work has shownthat sperm production depends on the testicles remaining cooler than the rest of the body, leading scientists to propose sitting for hours at a time can lead to a fall in sperm quantity.

The scientists say in the journal Human Reproduction: "The increase in scrotal temperatures observed in the present study in men driving cars could be one of the strongest pieces of evidence to explain the longer time required to achieve conception in men who are occupational drivers."

Thermometers attached to the scrotal sacs of nine healthy men measured an average temperature rise from 34.2C to 35.5C during the first 20 minutes of driving, stabilising at 36.2C after two hours.

Stewart Irvine, a specialist in male fertility at the Reproductive Biology Unit in Edinburgh, said higher scrotal temperatures are unlikely to be the main cause of the wider decline in sperm counts.