Background: Numerous health effects of smoking are well-known; associations with semen quality are uncertain. Most previous studies did not adjust for potential confounders and had limited information on age at smoking initiation or smoking cessation.
Methods: We investigated 1,631 healthy fertile men in the Nanjing Medical University Longitudinal Investigation of Fertility and the Environment (NMU-LIFE) study. Relationships were examined using multivariable linear regression controlling for potential covariates.
Results: We found a significant decrease in semen volume (β = -0.10, P = 0.001) and total sperm count (β = -0.42, P = 0.037), and significant increase in total motility (β = 6.02, P = 0.037) and progressive motility (β = 5.52, P = 0.037) in ever smokers of pack-years ≥10 compared with never smokers. We observed an inverse dose-dependent relation between smoking pack-years and semen volume (P < 0.001) and total sperm count (P = 0.010) and a positive dose-dependent relation between smoking pack-years and both total motility and progressive motility (P = 0.042 and 0.048, respectively). No significant differences in semen quality were detected among ever smokers with different ages at smoking initiation nor in former smokers compared with never smokers.
Conclusions: Cigarette smoking was associated with lower semen volume and total sperm count and higher sperm motility. Smoking cessation might have a restorative effect on semen quality. This finding has important implications for public health research and for understanding the development of abnormal semen quality.