NEW YORK (Reuters Health) - Being obese may dim a man's chances of becoming a father, even if he is otherwise healthy, a new study suggests.
Researchers found that among 87 healthy men ages 19 to 48, those who were obese were less likely to have ever fathered a child. More importantly, they showed hormonal differences that point to a reduced reproductive capacity, the researchers report in the journal Fertility and Sterility.
Compared with their thinner counterparts, obese men had lower levels of testosterone in their blood, as well as lower levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) -- both essential to reproduction.
According to the researchers, these relatively low levels of LH and FSH are suggestive of a "partial" hypogonadotropic hypogonadism. This is a condition in which the testes do not function properly due to signaling problems in the hypothalamus or pituitary gland, two brain structures involved in hormone secretion.
The findings suggest that obesity alone is an "infertility factor" in otherwise healthy men, write Dr. Eric M. Pauli and his colleagues at the Pennsylvania State University College of Medicine in Hershey.
Of the 87 men in the study, 68 percent had had a child. Pauli's team found that the average body mass index, or BMI, was lower among these men compared with those who'd never fathered a child; in the former group, the average BMI was 28, which falls into the range for "overweight," while the average BMI for childless men was nearly 32, which falls into the "obese" range.
When the researchers assessed the men for several reproductive hormones, they found that the more obese a man was, the lower was his LH and FSH levels. On the other hand, increasing obesity correlated with increasing estrogen levels.
Excess body fat, Pauli's team explains, may increase the conversion of testosterone to estrogen in a man's blood. Such hormone alterations could, in turn, signal the brain to suppress FSH and LH production.
Past studies have linked obesity with a dampened libido and increased risk of erectile dysfunction, the researchers note. Those effects, they say, along with the hormonal alterations seen in this study, could act together to decrease an obese man's fertility.
SOURCE: Fertility and Sterility, August 2008.