Being overweight might take a toll on men's fertility, a new study suggests.
Researchers from the Stanford University School of Medicine and the Eunice Kennedy Shriver National Institute of Child Health and Human Development found an association between being overweight (indicated by body mass index and waist circumference) and having a decreased sperm count, as well as decreased ejaculate volume.
"All aspects of semen quality are important," study researcher Dr. Michael Eisenberg told Reuters, who first reported on the study. "Ejaculate has several chemicals that provide a safer environment for sperm. As such, if the volume is low it may be a problem."
The study, which is published in the journal Human Reproduction, included data from around 500 couples who were part of the Longitudinal Investigation of Fertility and the Environment Study. They were recruited between 2005 and 2009 from Michigan and Texas. Data from 468 men were used for the study; the men had an average age of 31, an average BMI of 29.8 and an average waist circumference of 100.8 centimeters. (Body mass index is a ratio of height to weight; a BMI of 18.5 to 24.9 is considered normal weight, a BMI of 25 to 29.9 is considered overweight and a BMI of 30 and above is considered obese.)
Researchers found associations between higher BMI and waist circumference and declining ejaculate volume, as well as declining sperm count. They did not find associations between BMI and waist circumference and semen motility, vitality and concentration.
However, the "percentage of men with abnormal volume, concentration and total sperm increased with increasing body size," the researchers wrote in the study.
Previously, research presented at a meeting of the European Society of Human Reproduction and Embryology in 2008 showed that overweight and obese men had a higher likelihood of having low semen volume and sperm abnormalities, the Associated Press reported. The researchers of that study, from the University of Aberdeen, noted, though, that they were unsure whether those findings translated into difficulty having children.
Just this October, Harvard researchers found that processed meat intake seems to be associated with decreased semen quality in the form of lower concentration of sperm. It also seemed to affect the way sperm looked and was structured.
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