Nancy A. Melville

October 24, 2012

SAN DIEGO, California — As carbohydrate intake and dietary glycemic load increase, sperm concentration decreases, according to research presented here at the American Society for Reproductive Medicine (ASRM) 68th Annual Meeting.

Researchers analyzed data on 189 men 18 to 22 years of age who were enrolled in the Rochester Young Men's Study, conducted at the University of Rochester in New York, in 2009 and 2010.

The men's diets were assessed with a validated food frequency questionnaire, and semen samples were analyzed for sperm concentration, motility, and morphology.

The participants (82% white) had a mean body mass index (BMI) of 25.3 kg/m² and were highly physically active, spending an average of 11 hours per week on moderate to vigorous physical activity.

On average, about 50% of the men's diets was made up of carbohydrates.

After adjustment for factors such as total energy intake, age, abstinence time, BMI, smoking status, and the intake of protein, caffeine, and alcohol, the steady decline in sperm concentration was consistent with increasing quartiles of total carbohydrate intake (P for trend = .08): 49 million/mL (95% confidence interval [CI], 31 to 74) in the lowest quartile, followed by 47 million/mL (95% CI, 32 to 70), 37 million/mL (95% CI, 25 to 55), and 35 million/mL (95% CI, 23 to 51) in the highest quartile.

There was also an association between dietary glycemic load, which reflects the amount and quality of carbohydrates in the diet, and reduced sperm concentration (P for trend = .04). Adjusted sperm concentrations, from lowest to highest glycemic load, were 59 million/mL (95% CI, 39 to 91), 37 million/mL (95% CI, 26 to 55), 43 million/mL (95% CI, 29 to 62), and 32 million/mL (95% CI, 22 to 48).

Sperm motility was not associated with carbohydrate intake or with dietary glycemic load, and neither was morphology.

According to lead author Jorge E. Chavarro, MD, from the Department of Nutrition at Harvard Medical School in Boston, Massachusetts, data on the nature of dietary influences on sperm concentration, in general, are lacking.

Little is known about how diet and other modifiable lifestyle factors affect human fertility, but "it has been shown very consistently that being overweight or obese is strongly related to poor semen quality," he told Medscape Medical News.

"We also know that many of the systemic effects of obesity, such as chronic low-grade inflammation and insulin resistance, can be elicited by the composition of diet, independent of body weight," Dr. Chavarro explained. "With this in mind, we wanted to know if one aspect of diet, namely carbohydrate intake, was related to semen quality," he said.

The study's findings leave many questions unanswered, such as the mechanisms behind the relation between sperm concentration and carbohydrate intake.

"From our study, it is not possible to clearly identify which biologic mechanisms explain this relation, but there may be some overlap with the mechanisms explaining the relation between obesity and low sperm concentration," Dr. Chavarro said.

It is also unclear how sperm concentrations affect fertility.

The men in the study were young and "very physically active with untested fertility," he explained. "While previous studies have linked sperm concentration and other markers of semen quality to fertility rates, it is not possible from these data to predict the extent to which the observed differences in concentration translate into differences in fertility," he said.

"In addition, the data in this area are scarce, so it is very important that the findings are replicated before translating them into clinical recommendations," Dr. Chavarro said.

Male reproduction specialist Rebecca Z. Sokol, MD, president-elect of the ASRM, agrees that the findings, while intriguing, are inconclusive.

"The key word is trend, which tells us that it did not meet statistical significance," said Dr. Sokol, who is professor of obstetrics and gynecology and medicine at the Keck School of Medicine, University of Southern California, Los Angeles.

"It's an interesting idea, but we clearly need to evaluate more patients," she said. There is ongoing public interest in the association between diet and sperm count/fertility, but the evidence on any especially noteworthy nutritional interventions is slim, Dr. Sokol noted.

Patients ask what they can do to improve their sperm count and function, but "we're not sure if there is truly a nutritional aspect to improve sperm function," she explained.

"There have been small studies over a long period of time suggesting that certain changes in diet might affect fertility, but an association has not been clearly shown," she said. "In counseling fertility patients, the most important thing we can tell them is to do everything in moderation," Dr. Sokol concluded.

The study was supported by NIH grants T32DK007703-16 and P30DK46200, and European Union DEER Grant 212844. Dr. Chavarro and Dr. Sokol have disclosed no relevant financial relationships.

American Society for Reproductive Medicine (ASRM) 68th Annual Meeting: Abstract O-155. Presented October 23, 2012.