BMI influences hormone levels in overweight, obesity

By Sally Robertson, B.Sc.Dec 5 2012

A high body mass index (BMI) has no significant impact on parameters of sperm quality, although it does lower serum levels of testosterone, luteinizing hormone (LH), and prolactin, say researchers.

However, this negative impact of high BMI could potentially be counteracted with the use of aromatase inhibitors, they write in Andrologia.

"To our knowledge, this study is based on the second largest study population addressing this issue to date," comment Atiqullah Aziz (University of Regensberg, Germany) and colleagues.

Currently available data on this topic are conflicting and partially inconsistent, says the team, with some authors postulating that higher BMI affects ejaculate volume, total sperm, count, motile count, and sperm concentration, while others have found no such association of these parameters with BMI.

"One established possible effect of obesity on the male sexual hormonal system is the increased activity of adipocellular aromatase, which aromatises androgens and converts them into oestrogens, consequently resulting in lower testosterone levels," write the authors.

In the current analysis, which included 2110 men (aged a mean of 37.8 years) attending a fertility clinic between 1994 and 2010, no significant differences were found in average levels of pathologic sperm morphology, concentration, or motility, between men who were underweight (BMI <18.50 kg/m²), normal weight (BMI 18.50-24.99 kg/m²), overweight (BMI =25.00-29.99 kg/m²), or obese (BMI =30.00 kg/m²).

However, overweight and obese men had significantly lower mean testosterone levels than normal-weight men, at 4.47 versus 5.48 ng/mL.

Mean levels of LH were also significantly influenced by BMI, with overweight and obese man having significantly lower LH levels compared with normal-weight men, at 3.59 versus 3.91 U/L.

Commenting further on how higher aromatase activity may reduce hormone levels in overweight and obese men, Aziz and team explain: "Cytochrome aromatase P450 converts testosterone in estradiol. Therefore higher levels of circulating estradiol consequently contribute to a negative feedback on the gonadotropin secretion in the hypothalamic-pituitary-gonadal axis, which might explain lower LH levels."

The team also reports that men with pathologic versus normal BMI had significantly lower levels of prolactin, at 11.80 ng/mL versus 12.79 ng/mL, respectively. Two previous studies have described a link between the higher prolactin levels and the genesis and maintenance of adiposity, note the researchers, although they say that the current results did not demonstrate this.

"The use of aromatase inhibitors is a potential therapeutic approach for the treatment of infertile obese men," suggests the team.

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