Men’s fertility can be damaged by their weight, says research

Being too fat or thin can damage a man’s fertility, scientists said yesterday.

A study found that men of average weight had more healthy sperm than those outside the normal range.

They also had higher volumes of semen.

Previous research has shown an association between obesity and DNA damage in men’s sperm.

Dr Ghiyath Shayeb, from the University of Aberdeen, who led the study, said: “Our findings... seem to suggest that men who are trying for a baby with their partners should first try to achieve an ideal body weight.”

The researchers looked at the results of seminal fluid tests on 5,316 men attending Aberdeen Fertility Centre after having difficulties conceiving.

Body Mass Index (BMI) information was known for 2,037 of this group.

BMI measures a person’s weight relative to height. The “normal” BMI range is between 20 and 25, while someone with a figure of 30 or above is classified as clinically obese. A BMI of 19 or below is considered too low.

The study found that men with a “normal” BMI had more healthy-looking sperm — as judged by its appearance under a microscope — than men in the other groups. They also produced greater quantities of sperm.

Factors that might have affected the results, such as smoking, alcohol intake, age, social deprivation and length of time abstaining from sex, were all taken into account.

“Adopting a healthy lifestyle, a balanced diet, and regular exercise will, in the vast majority of cases, lead to a normal BMI,” said Dr Shayeb.

“We are pleased to be able to add improved semen quality to the long list of benefits that we know are the result of an optimal body weight.”

The findings were presented yesterday at the annual meeting of the European Society of Human Reproduction and Embryology (Eshre) in Barcelona.

Dr Shayeb now plans to compare male BMI in fertile and infertile couples.

“There has been a significant rise in the numbers of men with poorer semen parameters in the industrialised world, but this has not been reflected so far in male infertility,” he said.

“To compare male BMI in these two groups therefore seemed to us to be a logical next step.”

Further research was also needed to explore how obesity affects semen production, said Dr Shayeb.

“The mechanism for the relationship could be a number of things — different hormone levels in obese men, simple overheating of the testicles caused by excessive fat in, or that the lifestyle and diet that leads to obesity could also lead to poorer semen quality,” he added.

“We just don’t know the answer yet, but this is an important question that needs urgent attention.”