In some cases, these weight-related effects would likely be enough to reduce a man's fertility, said the researchers from the University of Southern Denmark, told Reuters Health. Men with a high or low BMI were more likely than normal-weight men to have a sperm count below 20 million per milliliter of semen, which is abnormally low.
On average, those men with a low BMI (defined as below 20) had a 36 percent lower sperm count than men with a normal BMI. Overweight men (BMI over 25) had a 24 percent lower sperm count compared with average-weight men.
In addition, the men's testosterone levels decreased as BMI increased, as did certain other reproductive hormones. It may be such hormonal effects of a high BMI that explain the poorer semen quality they found in overweight men.
The findings raise the possibility that the high prevalence of obesity in the Western world may be contributing to fertility problems. If that's the case, the researchers note that some cases of impaired fertility may be preventable.
However, it's not yet known whether maintaining a normal weight can help a man's chances of fathering children. To answer that question, researchers could study whether overweight men who shed their excess pounds show changes in semen quality.
Body weight has already been shown to affect a woman's ability to conceive. Obese women have a heightened risk of menstrual irregularities and infertility
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