Research by French fertility experts has provided the strongest evidence yet to back up the hypothesis that long hours spent driving could be linked to infertility in men and that the reason is likely to be the rise in scrotal temperature that occurs when men sit in vehicles.
A number of earlier studies have shown that sperm counts in professional drivers are lower, that their sperm has more abnormalities and that partners of men whose occupation is driving take longer to conceive.
But today's (Wednesday 31 May) report, published in Human Reproduction* is the first study to measure in a scientifically controlled experiment exactly what happens to scrotal temperature under normal driving conditions.
Nine healthy volunteers dressed in their usual clothing were 'wired up' by having skin thermometer probes (cutaneous thermocouples) attached to each scrotum and connected to a small data recorder fixed to their belts to record the temperature of the scrotum automatically every two minutes. The volunteers first walked outside along the same pre-determined route and then drove a car for 160 minutes without using air conditioning. A third probe connected to the data recorder measured the ambient temperature during the walking and driving periods.
The Toulouse-based research team found that during the first 20 minutes of driving, the men's mean scrotal temperature rose rapidly from 34.2 °C to 35.5°C. From 20 to 120 minutes it increased from 35.5°C to 36.2°C, then stabilised. A comparison between the mean scrotal temperature after two hours of driving and the mean scrotal temperature during walking showed that, while driving, the left scrotum was 1.7°C higher than while walking and the right scrotum was 2.2°C higher.
Dr Roger Mieusset, who lead the research by a team from the Human Fertility Research Group and CECOS Midi-Pyrénées, Toulouse, said: "Taken together with the data from other studies, the increase in scrotal temperature we measured in these drivers could be one of the strongest pieces of evidence yet to explain why the partners of occupational car drivers take longer to conceive.
"While the scientific background strongly suggests that an increase in scrotal temperature affects sperm formation, we need more research to confirm the possibility. However, our results indicate that male reproductive function is vulnerable from lifestyle factors."
*Increase in scrotal temperature in car drivers. Human Reproduction. Louis Bujan et al. Vol. 15. No 6. pp 1355-1357.
Notes:
1. Full embargoed text of the paper with participating research teams can be found from
09.00 BST Monday 29 May on website: http://www3.oup.co.uk/eshre/press-release/june.pdf
2. Human Reproduction is a monthly journal of the European Society of Human Reproduction and Embryology. Please acknowledge Human Reproduction as a source.
3 Printed text available on request from Dr Helen Beard, Managing Editor.
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