Fertility in the hot seat

“Men who use heated car seats could be unwittingly putting their fertility at risk”, The Daily Telegraph reports. The optimal temperature for producing healthy sperm is 35 to 36°C but a study in 30 healthy men has found that sitting in a heated car seat for 90 minutes increased the temperature of the scrotum by about 0.6°C compared with sitting in an unheated car seat. The lead researcher says that this increase “could be enough to damage sperm production”, the newspaper reports.

This study did not look directly at the effect of heated seats on male fertility, therefore it is not certain whether this increase in temperature would have any effect. In general, these findings should not be a cause for concern. Men who are experiencing subfertility may wish to consider switching off their car seat heating if they have to drive for long periods, but only as part of a wider programme to optimise fertility.

Where did the story come from?

Dr Andreas Jung and colleagues from the Justus Liebig University in Giessen and the Ford Research Centre in Aachen, Germany carried out this research. The study was funded by the Ford Research Centre, Aachen. It was published in the peer-reviewed medical journal: Fertility and Sterility.

What kind of scientific study was this?

This was an experimental laboratory study looking at the effect of heated car seats on scrotal temperature. The researchers enrolled 30 healthy male volunteers (age 20 to 53 years) from their university, who had no history of infertility and whose testes were normal when examined. For the experiment, temperature sensors were attached to the skin on either side of the scrotum and these were attached to a portable data recorder that took measurements every minute. All the volunteers were provided with clothing (cotton boxer shorts, trousers and two shirts in the appropriate sizes) to wear during the experiment. The room where the experiment was performed was maintained at 22°C, and volunteers spent 30 minutes acclimatising to room temperature before they started sitting in the car seats.

Volunteers sat in the same heatable car seat (a Ford Mondeo sport seat ST 220 heated with a 160W heater) for 90 minutes on two consecutive days at the same time of day. On one day, the seat heating was switched on after the volunteer sat down and on the other day it was not. The order in which this was performed (that is, heated seat on the first day or heated seat on the second day) was randomly selected for each volunteer. The seat heating equipment ensures that the temperature never increases above 42°C.

The temperature of the part of the seat directly below the testes was measured every minute during the experiment. Researchers controlled leg position by fixing the volunteers’ legs together with a band above and below the knees, so that their calves were at right angles to their thighs. They also measured core body temperature using an ear thermometer. After the experiments, the researchers compared scrotal temperature when the seat was heated with temperature when the seat was unheated.

What were the results of the study?

Scrotal temperature increased over the 90 minutes of sitting in both the heated and unheated seats. During the experiment, the highest temperature reached by the seat during heating was 39.7°C. The highest temperature reached by the scrotum during exposure to the heated seat was 37.9°C for the left side and 38.6°C for the right side. Scrotal temperature was about 0.5°C higher when the seat was heated than when it was not. The researchers found no difference in core body temperature between heated and unheated periods.

What interpretations did the researchers draw from these results?

The researchers concluded that their findings suggest that sitting in a heated car seat adds to the heat stress experienced by the scrotum, and therefore the testes. However, further studies are needed to determine whether this increase affects male fertility.

What does the NHS Knowledge Service make of this study?

This study was well controlled and illustrates that heated seats can raise the temperature of the scrotum. As the authors note, the effect was relatively small, and was smaller than the increases caused by sitting alone (without heat), shown in previous studies to be about 2ºC. It is not possible to draw conclusions about whether these increases in temperature would affect male fertility. Men who are experiencing subfertility may wish to consider switching off their car seat heating if they have to drive for long periods.

Sir Muir Gray adds... 

It would be better if they walked really.