Elsevier

European Urology

Volume 70, Issue 4, October 2016, Pages 635-645
European Urology

Platinum Priority – Review – Andrology
Editorial by Christian Leiber and Ulrich Wetterauer on pp. 646–647 of this issue
Cigarette Smoking and Semen Quality: A New Meta-analysis Examining the Effect of the 2010 World Health Organization Laboratory Methods for the Examination of Human Semen

https://doi.org/10.1016/j.eururo.2016.04.010Get rights and content

Abstract

Objective

Approximately 37% of men of reproductive age smoke cigarettes, with Europe having the highest tobacco use among all the World Health Organization (WHO) regions. Toxins from tobacco smoking can potentially affect sperm development and function, with a negative effect on semen parameters. Given the high prevalence of smoking and recent changes in the WHO laboratory methods for the examination of human semen, the role of this exposure in face of new WHO methods needs to be clarified.

Evidence acquisition

We conducted a systematic review, followed by a meta-analysis, to determine whether cigarette smoking affects human semen parameters. PubMed, Saint Joseph's University Discover, and Google Scholar were used to identify relevant studies published after release of the latest WHO methods for laboratory evaluation of human semen. Participants were from fertility/urologic clinics and andrology laboratories. The outcome measures were semen volume, sperm concentration, motility, and morphology, the parameters usually used in clinical settings to assess fertility.

Evidence synthesis

Twenty studies with 5865 participants were included in the meta-analysis. Exposure to cigarette smoking was associated with reduced sperm count (mean difference [MD]: −9.72 × 106/ml; 95% confidence interval [CI], −13.32 to −6.12), motility (MD: −3.48%; 95% CI, −5.53 to −1.44), and morphology (MD: −1.37%; 95% CI, −2.63 to −0.11). Subgroup analyses indicated that effect size was higher in infertile men than in the general population and in moderate/heavy smokers than in mild smokers. The overall effect size on semen volume, sperm count, and motility remained similar when 2010 and earlier WHO manuals were used for semen analysis but was lower with regard to sperm morphology.

Conclusions

Our results suggest that cigarette smoking has an overall negative effect on semen parameters. The latest WHO laboratory methods for the examination of human semen had a minimal impact on the magnitude of effect size, thus confirming the observed negative effect of smoking on conventional semen parameters.

Patient summary

A new systematic review and meta-analysis comprising 5865 men shows that cigarette smoking is associated with reduced sperm count and motility. Deterioration of semen quality is more pronounced in moderate and heavy smokers.

Introduction

Approximately 37% of male adults worldwide use tobacco, mainly cigarettes [1]. Smoking rates have gradually declined in the United States, but Europe still has the highest tobacco use among all the World Health Organization (WHO) regions [1], [2]. Tobacco combustion produces approximately 4000 chemical compounds, and smokers inhale a host of toxins including nicotine, carbon monoxide, cadmium, and other mutagenic compounds, all with potential deleterious effects on male germ cells [3]. The toxins originating from cigarette smoke can decrease sperm mitochondrial activity and damage the chromatin structure in human sperm, therefore impairing fertilization capacity both in vivo and in vitro [4], [5].

Smoking cigarettes has been associated with a deterioration of sperm quality including motility, concentration, and morphology, which are the parameters most frequently used in clinical settings to assess fertility [6], [7], [8]. However, the evidence is not unequivocal, and some studies have found no effect on semen quality [9], [10], [11].

In 2010, the WHO established new criteria for the laboratory examination of human semen [12]. The changes specifically included assessments of (1) volume by weight rather than graduated pipette; (2) motility by two categories, namely progressive and nonprogressive, in contrast with four categories in previous versions; and (3) morphology by strict criteria (Tygerberg) as opposed to the WHO criteria in previous manuals. New reference values for semen characteristics were also proposed that were markedly lower than those reported in previous manuals. In a recent study evaluating the impact of these changes, semen characteristics of approximately 15% of patients considered abnormal according to the 1999 WHO reference values were reclassified as normal based on the 2010 WHO reference values [13]. Therefore, varying results may be expected with regard to semen analysis when one manual is followed versus another, with obvious implications for counseling, diagnosis, and management of men seeking fertility evaluation. These data reinforce the need for a careful examination of the 2010 WHO criteria for the laboratory examination of human semen to help health care providers understand the clinical impact of such changes.

We conducted a systematic review and aggregated the available published data on the effect of cigarette smoking on semen parameters using a meta-analysis. The aim was to summarize the evidence of the effect of cigarette smoking on human semen characteristics in view of the new 2010 WHO criteria for the laboratory examination of human semen.

Section snippets

Search strategy

We conducted a systematic search using PubMed, Saint Joseph's University Discover (SJUD), and Google Scholar to identify all relevant studies published from 2010 to August 2015. For SJUD, which includes 189 databases (http://www.sju.edu/int/resources/libraries/drexel/), and PubMed, the Medical Subject Headings search terms used were *smoking* OR cigarette AND semen or sperm* OR *fertil* in any language. The following selections were made for the advanced search: “Only studies in humans” and

Description of studies

Supplementary Figure 1 provides a diagram of the review process. The characteristics of the included studies are provided in Table 1 [8], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39]. Participants were from infertility and urologic centers as well as andrology laboratories. All semen analyses followed the WHO guidelines.

Quantitative analysis

Overall, 20 studies were identified, and these included data on 5865 participants. The number of studies

Conclusions

Cigarette smoking was found to be a significant risk factor for decreased semen parameters in adult men. The WHO laboratory manual used for the examination of human semen had a negligible impact on the observed pooled effect size, except for sperm morphology. Given that most studies published after 2010 utilized previous manuals for semen analysis and considering that WHO methods will remain a reliable source for the laboratory evaluation of human semen, further research is needed to fully

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