High body mass index linked with poor semen quality in study

Denver-Being obese-or even overweight-increases a man's likelihood of infertility, according to a large study conducted at a single lab.

"Numerous studies show that obesity impairs male fertility," said co-author Ricardo P. Bertolla, DVM, PhD, head of research at São Paulo Federal University's Urological Research Center in Brazil. "We also observed this. The interesting thing is that all the men we included in the study underwent semen analysis at the same laboratory, so the same people were analyzing the semen for all these patients."

For the study, researchers retrospectively analyzed 943 patients aged 19 to 50 years who presented for assisted reproduction therapy at São Paulo Federal University's Human Reproduction Section between January 2004 and December 2008. Using subjects' body mass index levels, investigators divided subjects into three groups: eutrophic (BMI 20 kg/m² to 25 kg/m² ), overweight (BMI 25 kg/m² to 30 kg/m² ), and obese (BMI >30 kg/m² ). They then compared seminal parameters between these groups.

"The most interesting part of our results was that we saw that eutrophic men generally had a low frequency of azoospermia [6.1%; p<.05 versus the other groups]," Dr. Bertolla said at the 2010 American Society for Reproductive Medicine annual meeting in Denver. Rates of azoospermia in overweight and obese men were similar (12.3% and 14.9%, respectively).

"We saw that obese men had a lower sperm concentration and progressive motility than overweight or eutrophic men, and as a result, a lower number of total motile sperm," Dr. Bertolla added.

Specifically, obese men had an average sperm concentration of 49.7 million/mL, versus 60.7 million/mL and 71.8 million/mL for overweight and eutrophic men, respectively. Additionally, progressive motility figures were 47.7%, 48.9%, and 52.1%, respectively. Total motile sperm averaged 73.4 million, 80.9 million, and 125 million, respectively (in all three analyses, p<.05 for obese vs. the other two groups; overweight and eutrophic not different).

Varicocele was evenly distributed between the three groups, with a prevalence between approximately 36% and 39% in each group, Dr. Bertolla noted.

Overall, he said, "Overweight and eutrophic men had similar semen analysis results, so sperm quality was really only different in the obese group."

Losing weight may improve sperm quality

Among all patients, BMI averaged 33 kg/m² to 34 kg/m² , he added.

"High BMI values are associated not only with infertility, but also with a number of other alterations such as diabetes, metabolic syndrome, and cardiovascular disease," Dr. Bertolla explained. Therefore, he said, "From a clinical standpoint, it's important to advise men with a BMI above 30 kg/m² to lose weight anyway."

Study limitations include its retrospective nature and the fact that it did not exclude lifestyle factors such as whether patients smoked.

"We did not study, for example, what would happen if morbidly obese patients underwent gastric bypass surgery," Dr. Bertolla explained. (See related article, this issue.)

Accordingly, he said that investigators could not differentiate the impact of obesity versus the impact of a sedentary lifestyle on semen quality.

"We can't say that obesity is causing infertility, because the only true way to document that would be to see a fertile man and observe if he became infertile after gaining weight. But we were able to see that overweightness-and especially obesity-decreases the likelihood of having fertile semen."