Only Extreme Obesity Appears to Affect Male Reproductive Potential
Introduction: Previous studies suggest that men who are overweight or obese have an altered reproductive profile including decreased testosterone, sex hormone-binding globulin (SHBG), and inhibin B levels, and increased estradiol levels. However, the reproductive consequences of these changes are unknown.
Methods: A total of 438 male partners of subfertile couples were included in the analysis. Blood and semen samples were analyzed for sperm parameters and reproductive hormone levels.
Results: Confirming previous studies, higher BMI was associated with higher estradiol levels (P=0.01) and lower total testosterone and SHBG levels (P<0.001 for both comparisons). In addition, in extremely obese men (BMI ≥35 kg/m2), BMI was associated with decreased inhibin B levels (P<0.001) and testosterone: luteinizing hormone (LH) ratio (P=0.01). In terms of sperm parameters, only extremely obese men (BMI ≥35 kg/m2) had a significantly decreased total sperm count (P=0.04) compared with men of normal weight. Increasing BMI levels were linked to decreasing levels of ejaculate volume (P=0.01), and obese men (BMI >30 kg/m2) had significantly more sperm with high DNA damage (P=0.03). In contrast, BMI was not associated with sperm concentration, motility, or morphology.
Conclusion: While increasing body weight in men is associated with abnormal reproductive hormone levels, these alterations do not appear to impair semen markers for reproductive potential except in the extremely obese.
Tamara L. Wexler, MD, PhD, is an endocrinologist specializing in reproductive and neuroendocrinology, and an Attending in Medicine, Massachusetts General Hospital, Boston, MA.
The intent of this study was to examine the association of male weight not only with serum hormone levels but also with markers more closely tied to fertility, namely sperm parameters.
Chavarro and his colleagues designed this study to build on previous results (from others’ studies) demonstrating altered serum hormone profiles in overweight and obese men. To better elucidate the association between weight and fertility, they looked at sperm parameters including ejaculate volume; sperm concentration, morphology, and motility; and sperm DNA integrity, in addition to monitoring serum hormones.
The study population consisted of male partners in couples who were seen at the Massachusetts General Hospital Fertility Center 2000-2006 (n=483 after exclusions; mean age 36.3 years). Exclusion criteria included azoospermia; while underweight men were included in the cohort, the number (n=4) was too small to allow meaningful analysis, and those men were thus also excluded. Men with normal BMI (18.5-24.9 kg/m2) were used as the reference group. Three-quarters of the subjects were overweight or obese (233 overweight, 87 moderately obese men, 40 men > severely obese.)
When possible, outcome measures were dichotomized by established reference values (ie, normal or outside the range of normal). Multivariate analysis allowed for lifestyle factors including caffeine, alcohol, and tobacco; reproductive history; and age and race. There was no statistically significant difference in these factors across BMI.
The study found that higher BMI was associated with changes in serum hormones seen in other studies: lower serum total testosterone, SHBG, and inhibin B, and higher serum estradiol. The authors provided a measure of association: for each 1 kg/m2 increase in BMI, total testosterone was lower by 7.4 ng/dL. In men with abnormal semen parameters, higher BMI was associated with lower serum LH and follicle-stimulating hormone levels, despite the lower inhibin B and testosterone levels which would be expected to stimulate higher LH and FSH production via feedback mechanism; the authors posit a weight-related impairment of hypothalamic-pituitary-testes feedback, most notably in men who also show semen abnormalities.
There was a trend towards a greater number of sperm with high DNA damage, and decreased semen volume, with increasing BMI; after adjusting for lifestyle, reproductive history, and abstinence time, the association reached significance. While there were no significant differences in sperm concentration, morphology, or motility across BMI categories, there was a lower total sperm in men with the highest BMI (>35 kg/m2), presumably related to the observed lower ejaculate volume (with preserved concentration). In contrast, the authors note, the preponderance of prior work has found an association between BMI and lower sperm concentration but no difference in ejaculate volume.
This study confirmed the association between weight and serum hormone levels (total testosterone, inhibin B, estradiol). It found that obesity alone was associated with increased sperm DNA damage, and that a lower sperm count was noted only in the most obese group (BMI >35 kg/m2). The differences in hormone levels observed with excess weight do not, per these results, appear to be associated with abnormal sperm parameters.
To determine the impact of weight on fertility in men, studies may thus need to incorporate measures more closely tied to observed reproductive potential (whether semen parameters or pregnancies.)