Obese Men Have Less Semen, More Sperm Abnormalities

Dr. Shayeb and colleagues looked at the results of seminal fluid analysis in 5316 men attending Aberdeen Fertility Centre with their partners for difficulties in conceiving. 2037 of these men had complete data on their BMIs. "We felt that it was possible that male overweight might contribute to fertility problems," he said, "particularly since it is a known risk factor for problems in conceiving among women."

The scientists divided the men into four groups according to their BMI, from being underweight to being considerably overweight. Taking into account other characteristics that could confound the analysis, such as smoking, alcohol intake, age, social deprivation, and the length of time of abstinence from sex prior to producing a semen sample for analysis, they looked for a relationship between BMI and semen quality. The analysis showed that the men in Group B, who had an optimal BMI (20-25, as classified by WHO), had higher levels of normal sperm than those in the other groups. They also had higher semen volume. There was no significant difference between the four BMI groups in sperm concentration or motility.

The researchers did not look at DNA damage in the sperm, preferring to look at the parameters of the routine semen analysis, which all men attending the fertility centre will have at least once. "Other studies have suggested an association between male obesity and increased DNA damage in the sperm, which can be associated with reduced fertility as well," said Dr. Shayeb.

"Our findings were quite independent of any other factors," he said, "and seem to suggest that men who are trying for a baby with their partners, should first try to achieve an ideal body weight. This is in addition to the benefit of a healthy BMI for their general well being.

"Adopting a healthy lifestyle, a balanced diet, and regular exercise will, in the vast majority of cases, lead to a normal BMI. 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 team intends to follow up their research by comparing male BMI in fertile and infertile couples to see if the poorer semen quality correlates with reduced fertility. "There has been a significant rise in the numbers of men with poorer semen parameters in the industrialised world," said Dr. Shayeb, "but this has not been reflected so far in male infertility. To compare male BMI in these two groups therefore seemed to us to be a logical next step."

Further research is also needed on exactly 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 the area, or that the lifestyle and diet that leads to obesity could also lead to poorer semen quality. We just don't know the answer yet, but this is an important question that needs urgent attention."