Overweight and Obese Men Are At Increased Risk for Abnormal Sperm Counts: A Meta-Analysis
Introduction: This systematic review and meta-analysis was designed to study the association between BMI and sperm count.
Methods: A systematic review of relevant literature up until June 2012 yielded 21 studies. Unpublished data from 717 men who attended a single infertility clinic were also included in the analysis. Together, the meta-analysis included data on 13,077 men from the general population and those who attended fertility clinics. BMI was stratified using World Health Organization categories: underweight <18.5 kg/m2; normal weight 18.5-24.9 kg/m2; overweight 25.0-29.9 kg/m2; obese 30.0-39.9 kg/m2; and morbid obesity ≥40 kg/m2. Total sperm count was categorized as follows: normozoospermia (≥40 × 106 spermatozoa per ejaculate), oligozoospermia (<40 × 106 but >0 spermatozoa per ejaculate), and azoospermia (absence of spermatozoa).
Results: A J-shaped association was found between BMI categories and abnormal sperm count (defined as azoospermia or oligozoospermia). The odds ratio (OR) for abnormal sperm count was 1.15 for underweight men, 1.11 for overweight men, 1.28 for obese men, and 2.04 for morbidly obese men, compared with men of normal weight. A similar J-shaped association was found between BMI and abnormal sperm concentration. These associations were all statistically significant with the exception of the OR for abnormal sperm count among underweight men and for abnormal sperm concentration among overweight men.
Conclusion: Obese and overweight men are at significantly increased risk for abnormal sperm count.
Tamara L. Wexler, MD, PhD, is an endocrinologist specializing in reproductive and neuroendocrinology, and an Attending in Medicine, Massachusetts General Hospital, Boston, MA.
Sermondade and colleagues undertook a systematic review and meta-analysis of literature looking at BMI and sperm count, including unpublished data on 717 subjects seen at an infertility center in France between 2007-2010. Standardized data was obtained from the authors of the studies (required for inclusion), resulting in the ability to analyze original and complete data for 20 published studies (from 25 publications).
The cohort included 13,077 men from 21 studies; the normal weight group (BMI 18.5-<25 kg/m2) was used as a reference. The mean age of the men in individual studies ranged from 19.5 to 46.4 years.
Outcome measures included sperm count, dichotomized to normal or abnormal (<40M/ejaculate), and sperm concentration, also dichotomized (abnormal >15M/ml). A J-shaped relationship was noted between BMI and abnormal sperm count and concentration. The results were statistically significant (95% CI did not cross 1.0) other than for the OR for abnormal count for underweight men and the OR for abnormal concentration for overweight men. Similar results were seen when the unpublished data were excluded, and when oligozoopermia and azoospermia were considered separately.
It has been shown that underweight as well as overweight in women may have a negative impact on fertility (see Weight and Fertility: A Review). While the increased OR for sperm count for underweight men (1.11, 95% CI 0.93-1.43) did not reach statistical significance in this meta-analysis, this may be related to the relative paucity of underweight men in the combined studies; the majority of the cohorts included in this meta-analysis included <1% men with BMI <18.5 kg/m2. Alternately, it may be that the association with sperm concentration is stronger for low BMI (OR 1.46, 95% CI 1.14-1.88).
This meta-analysis represents a large number of subjects, and is strengthened by the aggregation of individual subject data. Of note, the populations of the individual studies were varied, most notably with respect to known infertility. Individual studies of men without known infertility and subfertile men have shown differing results. This meta-analysis excluded studies for which individual standardized data could not be obtained; the authors estimate that this may in fact have led to underestimation of the ORs. The meta-analysis did not consider other measures that may be relevant for fertility, such as weight circumference, or functional sperm tests.
The meta-analysis by MacDonald and colleagues1 published in 2010 concluded that BMI was not associated with decreased sperm concentration or count; while the review included 31 studies published through February of 2009, the meta-analysis aggregated data from 5 studies. This meta-analysis by Sermondade and colleagues included 21 studies through June of 2012 (many from the years since the MacDonald meta-analysis), and was able to use individual subject data collected from the authors. It is also important to note that the association seen by Sermondade and colleagues was statistically significant only when sperm concentration was dichotomized; mean sperm concentrations themselves did not differ significantly across BMI groups.
In summary, this meta-analysis suggests that overweight and obesity increase the risk for abnormal sperm count, and underweight and obesity increase the risk for abnormal sperm concentration.
1. MacDonald AA, Herbison GP, Showell M, Farquhar CM. The impact of body mass index on semen parameters and reproductive hormones in human males: a systematic review with meta-analysis. Hum Reprod Update. 2010;16(3):293-311.