Greater BMI and Waist Circumference Linked to Abnormal Semen Parameters in Men Without Known Infertility
Introduction: While some studies suggest that men with a higher body mass index (BMI) are at greater risk for impaired sperm production, other studies have not found this relationship. In addition, the majority of previous studies only studied BMI as a measure of overall adiposity without considering body fat distribution. Moreover, little is known about the impact of exercise on male infertility. This study was designed to study whether BMI, waist circumference (WC), and physical activity have independent effects on semen quality.
Methods: Researchers examined data from 468 couples enrolled in the population-based prospective Longitudinal Investigation of Fertility and the Environment (LIFE) study. The male partners did not have known infertility. The men were asked about their medical and reproductive history, lifestyle, and physical activity levels, including via in-person interviews; underwent standardized anthropometric assessment; and submitted semen samples. BMIs of <25.0 kg/m2 were classified as underweight and normal (one group), 25.0–29.9 kg/m2 as overweight, 30.0–34.9 as class I obese, and ≥35 kg/m2 as class II obese.
Results: Analysis of semen quality parameters showed that increasing BMI and WC were linked to a linear decline in semen volume (P<0.01), after adjusting for select covariates (age, college education, and smoking status). Waist circumference, but not BMI, was linked to a linear decline in total sperm count (P<0.01), with men in the highest WC category (≥101.6 cm) having a 22% lower total sperm count compared with men in the lowest WC category. In contrast, neither BMI nor WC was statistically significantly associated with semen concentration, vitality, morphology, or DNA fragmentation index (P values of <0.05 were considered statistically significant). Physical activity was not associated with any semen parameters.
When examining dichotomized abnormal semen quality end-points, higher BMI was linked to a greater percentage of men with low sperm volume (<1.5 mL; P=0.033), low sperm concentration (<15 M/mL; P=0.028), and low total sperm count (<39 M; P=0.005). Waist circumference was associated with both low sperm concentration (P=0.025) and low total sperm count (P=0.008).
Conclusion: Adiposity—whether assessed by BMI or WC—is associated with decreased sperm production in men without known infertility. Overweight and obese men had a higher incidence of low sperm volume, low semen concentration, and low total sperm count. Physical activity did not appear to impact semen quality parameters.
Tamara L. Wexler, MD, PhD, is an endocrinologist specializing in reproductive and neuroendocrinology, and an Attending in Medicine, Massachusetts General Hospital, Boston, MA.
This paper is designed to examine the relationship between weight, body fat distribution (as measured by waist circumference (WC)), physical activity, and semen parameters. Drawing on reports that body fat distribution may better predict potential negative health sequelae than weight alone, the authors included WC measurements. In contrast to the several other studies that incorporated WC (eg, Hammiche et al, 2012 ), this group looked at men who were not known to be infertile. Outcome parameters included ejaculate volume, total sperm count, and semen concentration.
The included population consisted of 468 male partners of couples attempting fertility, drawn from the U.S.-based LIFE study (2005-2009). The average age of the subjects was 31.8 years, average BMI 29.8 (82% overweight or obese), with 58% reporting <1 weekly physical activity; as with all studies, the specifics of the included cohort inform the generalization of the results.
Information was gathered by in-person interviews and measurements, and the data would thus be expected to be more reliable than self-reported survey data; measurements were gathered in a standardized fashion (eg, WC measured at a set location on each participant, all semen measured in the same lab).
The authors found that higher BMI and larger WC were associated with reduced semen volume, and that WC was inversely related to total sperm count. The most obese men and those of normal BMI both displayed lower incidence of abnormal sperm DNA fragmentation than overweight men [dichotomized parameters based on WHO references]; the relevance of this is unclear. While the authors set out to evaluate the relationship between physical activity and semen parameters, the sedentary nature of the subjects rendered difficult any conclusions regarding exercise. Further information will come from studies looking at the effect of weight and activity on direct measurement of fertility (or implications of sperm parameters for fertility) as well as the impact of weight loss.