BMI had no impact on sperm concentration, motility, or morphology in overweight men, study says.

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SAN FRANCISCO—Overweight men are no more likely to be infertile than normal-weight men, according to study findings presented here at the annual meeting of The Endocrine Society. 

The study showed that sperm concentration, motility, and morphology are unaffected by increasing BMI, even when it is high enough to reduce testosterone levels. But the use of elective serotonin reuptake inhibitors may have a negative impact on sperm.

“We see pretty significant deficits in fertility in women due to obesity, so we thought we’d see an effect in men,” said study investigator Nanette Santoro, MD, professor of reproductive endocrinology at Albert Einstein College of Medicine, Bronx, N.Y. “But that wasn’t the case.”

Despite other studies reporting significant inverse associations between BMI and normal sperm cells, as well as epidemiologic observations of reduced fertility with high BMI in men, she and her colleagues did not observe any association between any semen parameters and BMI.

Dr. Santoro and her colleagues looked at 292 men who gave semen samples at fertility clinics. All subjects were between the ages of 18 and 50 years and, on average, had a BMI of 28 kg/m2, which is considered nearly obese. Overall, greater body weight was not associated with worse sperm production or sperm motility.

Only a BMI of 35 kg/m2 or greater had a negative impact on sperm, but Dr. Santoro noted that the study included only a small number of men in this category. Increasing body weight was linked to lower testosterone in the 31 participants for whom testosterone was measured, but Dr. Santoro said low testosterone causes infertility only if it is extremely low or occurs in morbidly obese men.

“Our results show that the process of making sperm is pretty robust and is hard to interrupt,” Dr. Santoro said. “It’s good news for men that body size may be less related to fertility than it is in women.”

Of the 292 men, 39 were current smokers and 20 were past smokers. The researchers observed no association between smoking status and sperm parameters. Use of selective serotonin reuptake inhibitors was reported by six of the men, and researchers found a trend toward reduced sperm motility in them.