A study published within the Science of the Total Environment Journal investigates the contribution of air pollutants-induced semen damage to the chance of infertility.

Study: Semen damage contributed over 50 % to air-pollutant-induced infertility: A prospective cohort study of 3940 men in China. Image Credit: olliulli/Shutterstock.com

Background

Human reproductive health faces major challenges worldwide due to many aspects, including genetic, environmental, lifestyle, and psychological aspects. Air pollutants, as a significant source of environmental pollution, are known to affect sperm quality negatively. 

In response to the World Health Organization (WHO), the worldwide prevalence of infertility is at the least 15%, meaning about 60 to 80 million couples are infertile globally. Male infertility contributes to about 40 to 70% of overall infertility observed globally.

Studies conducted in animals have shown that air pollutants, including particulate matter (PM), reduce sperm quality and impair spermatogenesis, resulting in reduced fertility.

Nonetheless, insufficient evidence is on the market to know the impact of air pollutant-induced sperm damage on the chance of infertility within the human population.

In the present study, scientists have assessed the impact of multiple air pollutants on semen parameters and male infertility.  

Study design

The study was conducted on 3,940 men aged 22 to 49 years. The participants were enrolled between November 2018 and April 2021. At enrollment, semen samples were collected from the participants, and eight semen parameters (semen volume, sperm concentration, total sperm count, progressive motility, total motility, vitality, sperm morphology, and sperm deformity index) were analyzed.

In the course of the study follow-up period of 12 months, the infertility rate was assessed among the many participants. Infertility was defined as being unable to get pregnant after unprotected intercourse inside 12 months.

Machine learning algorithms were used to estimate concentrations of multiple air pollutants and assign them to every participant. The pollutants included within the evaluation were PM2.5, PM10, sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), and carbonic oxide (CO).

Statistical analyses were conducted to find out the connection between each air pollutant and semen parameters, the collective effects of the pollutants on semen parameters, and the effect of pollutant-induced semen damage on male infertility.

Participants’ exposure to air pollutants was calculated for as much as 90 days before the clinic visit. These exposures were divided into 4 potential susceptibility time windows, including the complete period of spermatogenesis, epididymal storage, sperm motility development, and spermatocytogenesis.  

Vital observations   

The evaluation of the consequences of air pollutants on semen parameters in the course of the 90-day exposure period revealed significant negative effects of SO2 and O3 on sperm morphology and progressive motility and vitality, respectively.

While PM2.5, PM10, and NO2 showed an association with sperm morphology, O3 and NO2 showed an association with sperm deformity index.

Regarding susceptibility time windows, the findings revealed that different air pollutants have different susceptibility windows for semen parameters.

The impact of SO2 and O3 on sperm morphology and progressive motility and vitality, respectively, was observed during the complete period of spermatogenesis (90 days).

The impact of PMs and NO2 on sperm morphology and sperm deformity index was observed in the course of the spermatocytogenesis period. Regarding sperm deformity index, the consequences of PMs and O3 were observed in the course of the epididymal storage period and sperm motility development period, respectively.

Considering all tested pollutants, a collective negative impact was observed on sperm concentration. A suggestive negative impact was also observed on vitality.

The evaluation of the connection between pollutants and infertility risk revealed that SO2-induced alteration in sperm morphology significantly increases the chance of male infertility. Specifically, altered sperm morphology accounted for roughly 60% of the full effect of SO2 on male fertility.

Study significance

The study identifies multiple air pollutants with different susceptibility time windows able to altering various semen parameters.

Amongst these pollutants, SO2 must be monitored fastidiously, because it has a big negative impact on sperm morphology during the complete period of spermatogenesis, and SO2-induced changes in sperm morphology is usually a major contributor to male infertility.

As mentioned by the scientists, with an observational study design, they might not determine the causal relationship between air pollutants and semen parameters.

Furthermore, all participants were recruited in a single center, which may potentially impact the representativeness of the study population. Subsequently, further studies must be undertaken that include a bigger and more diverse sample size.