A recent systematic review by Carré et al. reviewed the effects of air pollutants on fertility for Men and Women. Air pollution has been shown to significantly affect general health in a negative way. It can contribute to the development or worsening of respiratory and cardiovascular health issues (i.e. lung cancer, stroke, asthma, and more). Research evaluating the effect of these same pollutants specifically on fertility have been lacking.
Specifically, exposure to polycyclic aromatic hydrocarbons (PAH), heavy metals (zinc, copper, lead, and more), and nitric dioxide (NO2).
How Do These Pollutants Interfere with Fertility?
Various mechanisms have been postulated. One of the methods by which these pollutants can interfere with fertility is by disrupting hormone function. They may have what is known as an anti-estrogenic, estrogenic, and anti-androgenic effects. This means they can block the effect of estrogen, stimulate the effect of estrogen, and block the effect of androgen hormones in the body, overall leading to a disruption in reproductive hormonal balance and function.
A different mechanism that allows these pollutants to affect fertility is by creating oxidative stress. The creation of reactive oxygen species (ROS) can cause damage to cellular organs, damage DNA, and damage the cell wall. All of the mentioned consequences of ROS can decrease egg and sperm quality.
Finally, the last mechanism by which these chemicals can interfere with reproduction is by directly altering the expression of certain genes. It can interfere with gene methylation and therefore expression of its downstream proteins.
Which Air Pollutants are worse?
It was difficult to identify a single air-pollutant as an individual cause or contributor to infertility, however, the combination of particular matter, heavy metals, and polycyclic aromatic hydrocarbons seems to have a negative effect.
Impact of Air Pollutants on IVF Outcomes
High levels of Nitric Dioxide exposure seem to have the biggest effect in lowering IVF success rates. Exposure to nitric dioxide during the following times lowered IVF success rate: period of stimulation to trigger, from trigger to retrieval, and from embryo transfer to pregnancy test. There was a significantly larger negative impact on success rates when exposure occurred during the period from embryo transfer to pregnancy test. The estimated decrease in IVF success rate from NO2 exposure was about 24% (Odds Ratio of 0.76). Another study also found that exposure to large particulate matter, while not affecting IVF success rates, may contribute to an increased miscarriage rate. A separate study observed that exposure to large particulate matter during the follicular phase almost doubled the miscarriage rate, regardless of whether the pregnancy was natural or from IVF.
Conclusion
Overall the quality of these studies was very low since they are observational studies. However, the compilation of animal and human studies on the subject reveals a common trend that air pollutants can negatively affect reproductive health.
References:
Carré, J., Gatimel, N., Moreau, J., Parinaud, J., & Léandri, R. (2017). Does air pollution play a role in infertility?: a systematic review. Environmental Health,16(1).