Men who are overweight or obese have lower sperm counts and lower ejaculate volumes, according to the results of the first study to make this association in men who were trying to conceive but who did not have known infertility.
“Our study provides further data showing the link between being overweight and sperm quality,” lead author Dr Michael Eisenberg of Stanford University School of Medicine told ConsultantLive.
“Most prior studies examined infertile men only, while our study examines all men who were trying to conceive,” Dr Eisenberg stated. “Moreover, we looked at both body mass index (BMI) as well as waist circumference to determine the relationship with sperm production.”
Dr Eisenberg and colleagues examined data from the Longitudinal Investigation of Fertility and the Environment Study, a population-based prospective cohort of more than 500 couples attempting to conceive in Texas and Michigan.
They analyzed data from 468 men, mean age 32, the majority of whom (82%) were overweight or obese. More than half said they participated in physical activity less than once a week. Fewer than 10% were oligospermic.
“When examining semen parameters, ejaculate volume showed a linear decline with increasing BMI and waist circumference. Similarly, the total sperm count showed a negative linear association with waist circumference,” said Dr Eisenberg.
A man in the normal BMI range had an ejaculate volume of 3.3 mL, compared with 2.8 mL for men who were severely obese.
Men with the largest waists, more than 40 inches, had about 22% lower total sperm count compared with men who had waist measurements under 37 inches.
The percentage of men with abnormal volume, concentration, and total sperm increased with increasing body size.
There was no significant relationship seen between body size and semen concentration, motility, vitality, morphology, or DNA fragmentation index.
“Body size as measured by BMI or waist circumference is negatively associated with semen parameters with little influence of physical activity,” Dr Eisenberg noted.
Primary care physicians need to get across the message that the heavier the man, the higher the chances of a low sperm count, Dr Eisenberg suggested. “I think bringing attention to another adverse outcome of obesity is important,” he said. “Let men know that in addition to health aspects, obesity may also impair reproductive goals.”
It’s still unknown what a reduction in body weight does to the sperm counts of men starting with a low sperm count, Dr Eisenberg noted. “We don't have a good answer at this point,” he said. “However, we do know that weight loss helps overall health, so at a minimum we can expect a health benefit for an overweight man who loses weight.”
Dr Eisenberg stated that primary care physicians need to “bring awareness to this relationship. This may provide another motivation for men to change lifestyle habits, knowing that it can impact fertility.”
In addition, as men discuss plans for starting a family, this study can provide important information as to who may be at risk for impaired fertility, he noted.
The researchers reported their results online on December 4, 2013 in the journal Human Reproduction.