To what extent does air pollutant-induced semen damage contribute to male infertility?

A study published in the Science of the Total Environment Journal investigates the contribution of air pollutants-induced semen damage to the risk 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 because of many factors, including genetic, environmental, lifestyle, and psychological factors. Air pollutants, as a major source of environmental pollution, are known to impact sperm quality negatively. 

According to the World Health Organization (WHO), the global prevalence of infertility is at 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, leading to reduced fertility.

However, insufficient evidence is available to understand the impact of air pollutant-induced sperm damage on the risk of infertility in the human population.

In the current 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.

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

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

Statistical analyses were conducted to determine the relationship 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 up to 90 days before the clinic visit. These exposures were divided into four potential susceptibility time windows, including the entire period of spermatogenesis, epididymal storage, sperm motility development, and spermatocytogenesis.  

Important observations   

The analysis of the effects of air pollutants on semen parameters during 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 entire period of spermatogenesis (90 days).

The impact of PMs and NO2 on sperm morphology and sperm deformity index was observed during the spermatocytogenesis period. Regarding sperm deformity index, the effects of PMs and O3 were observed during 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 analysis of the relationship between pollutants and infertility risk revealed that SO2-induced alteration in sperm morphology significantly increases the risk of male infertility. Specifically, altered sperm morphology accounted for approximately 60% of the total effect of SO2 on male fertility.

Study significance

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

Among these pollutants, SO2 should be monitored carefully, as it has a significant negative impact on sperm morphology during the entire period of spermatogenesis, and SO2-induced changes in sperm morphology can be a major contributor to male infertility.

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

Moreover, all participants were recruited in a single center, which can potentially impact the representativeness of the study population. Therefore, further studies should be undertaken that include a larger and more diverse sample size.

Written by

Dr. Sanchari Sinha Dutta

Dr. Sanchari Sinha Dutta is a science communicator who believes in spreading the power of science in every corner of the world. She has a Bachelor of Science (B.Sc.) degree and a Master's of Science (M.Sc.) in biology and human physiology. Following her Master's degree, Sanchari went on to study a Ph.D. in human physiology. She has authored more than 10 original research articles, all of which have been published in world renowned international journals.