BUSINESSMEN and teenage boys could be risking their fertility by using laptop computers, research suggests.

The combination of heat generated by the computers and the posture needed to balance the equipment on the lap leads to raised temperatures around the scrotum, a study has found. Past research shows that higher scrotal temperatures can damage sperm and affect fertility. And the introduction of new technology such as Bluetooth and infrared connections — which provide wireless links to the internet — has resulted in a growing number of men using the machines on their thighs rather than at a desk.

To keep the testicles at an ideal temperature — and for greater comfort — men naturally sit with their legs further apart than women. When working on a laptop, however, they will adopt a less natural position in order to balance it on their laps, which results in a significant rise in body heat between their thighs.

The latest findings, published in the journal Human Reproduction, give warning that teenagers and young men should consider cutting the time spent with a computer positioned on their lap because of the possible long-term damage to their fertility. Researchers from the State University of New York said their study was the first to look at the effect of heat from laptop computers on scrotal temperature.

Using 29 volunteers aged 21 to 35, the researchers, led by Yefim Sheynkin, found that sitting with the thighs together to balance a laptop caused scrotal temperatures to rise by 2.1C. But when the laptop was in use, average temperatures rose by 2.6C on the left of the scrotum and 2.8C on the right.

Research this year showed that sperm counts have dropped by almost a third in a decade. A study of 7,500 men who attended the Aberdeen Fertility Centre, at the University of Aberdeen, between 1989 and 2002, showed average sperm concentrations fell by nearly 30 per cent. The reasons are unclear, but drug use, alcohol, smoking and obesity are factors. Pesticides, chemicals and radioactive material have also been linked to decreases in fertility.

Now the growing popularity of laptops could also affect sperm production.

Dr Sheynkin said: “By 2005, there will be 60 million laptops in the US and 150 million worldwide. Continued improvements in power, size and price have favoured their increased use in younger people and laptop sales now exceed those of desktop computers.”

The researcher said that laptops could reach internal operating temperatures of more than 70C (158F).The average surface temperature of the computers used in the experiment increased from nearly 31C (87.8F) at the start of the test to nearly 40C (104F) after one hour.

“The body needs to maintain a proper testicular temperature for normal sperm production and development,” Dr Sheynkin said. “Portable computers in a laptop position produce scrotal hyperthermia by both the direct heating effect of the computer and the sitting position necessary to balance the computer.”

Dr Sheynkin said they did not know the exact frequency and time of heat exposure that would lead to reversible or irreversible changes to sperm. But he said that frequent use of laptops over years without sufficient recovery time between exposures “may cause irreversible or partially reversible changes in male reproductive function”.

The study found that within the first 15 minutes of using a laptop, scrotal temperatures had increased by 1C (33.8F).

“Until further studies provide more information on this type of thermal exposure, teenage boys and young men may consider limiting their use of laptop computers on their laps, as long-term use may have a detrimental effect on their reproductive health,” Dr Sheynkin said.

COMPUTERS — THE VITAL STATISTICS

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