Does smoking affect male fertility?

Impact of Smoking on Male Fertility

Smoking has a negative effect on male fertility through its detrimental impact on semen quality, including reduced sperm concentration, motility, and morphology, despite potentially increasing testosterone levels. 1 Men trying for pregnancy should abstain from smoking to optimize their fertility potential.

Effects of Smoking on Male Reproductive Parameters

Semen Quality

• Smoking negatively affects key sperm parameters:
  • Reduced sperm concentration (oligozoospermia)
  • Decreased sperm motility (asthenozoospermia)
  • Abnormal sperm morphology (teratozoospermia) 2
  • Increased DNA fragmentation 3

Hormonal Effects

• Interestingly, smoking is associated with increased rather than decreased testosterone levels:
  • Smokers have approximately 15% higher total testosterone
  • 13% higher free testosterone compared to non-smokers 4
  • Several studies report increased serum testosterone in smokers 1, 4

Oxidative Stress Mechanism

• Cigarette smoke increases reactive oxygen species (ROS) in the reproductive system
• This oxidative stress damages sperm DNA and impairs sperm function 5
• DNA fragmentation compromises chances of pregnancy 3

Evidence Quality and Limitations

The WHO guidelines (2017) note that the evidence regarding smoking's effect on male fertility has inconsistencies:

• Some studies show clear negative effects on semen parameters
• Other studies fail to demonstrate a direct impact on fertility outcomes
• The WHO strongly recommends abstaining from smoking based on moderate quality evidence 1

Key limitations in the research include:

• Inconsistent definitions of smoking status across studies
• Self-reporting bias in smoking assessment
• Varied study populations (fertility clinic patients vs. general population)
• Limited studies examining time-to-pregnancy (TTP) as an outcome 1

Clinical Implications

For Men Actively Trying to Conceive

• Complete smoking cessation is recommended for men planning fatherhood 1, 6
• This applies to both traditional cigarettes and electronic cigarettes (vaping) 6
• Men with marginal semen quality may particularly benefit from quitting smoking 7

For Men with Fertility Issues

• Heavy smoking is associated with more severe semen abnormalities 2
• Even light smoking can cause asthenozoospermia, which may be an early indicator of reduced semen quality 2
• Smoking cessation may improve semen parameters, though more research is needed on recovery after quitting 7

Beyond Fertility Concerns

• Paternal smoking may have implications for offspring health:
  • Potential increased risks for congenital anomalies
  • Possible association with childhood cancers 7
  • Impact on embryo quality 3

Conclusion

While the American Society for Reproductive Medicine (ASRM) previously concluded there was insufficient evidence linking smoking to male infertility, the WHO now strongly recommends that men trying for pregnancy should abstain from smoking based on moderate quality evidence showing negative effects on semen quality 1. This recommendation is further supported by smoking's known adverse effects on general health and potential impacts on offspring health.