Infertility (the inability to conceive following a year of unprotected sex) affects 14% of couples in the UK. Men are often overlooked during the fertility journey, yet male infertility accounts for around 50% of infertility cases.
Evidence has shown that sperm quality has been decreasing over the 21st century. Explanations behind the decline are not fully understood but there is a growing belief that environmental factors are having a huge impact.
A recent study emerging in JAMA Network has found an association between particulate matter (PM) air pollution and reduced sperm motility, the ability of sperm to move efficiently.
PM is a mixture of solid and liquid particles in the air including dust, soot and smoke. One notable PM event was the London smog in 1952, which directly led to 4,000 deaths and 100,000 suffering adverse health effects due to the high levels of air pollution. Despite this being an extreme example, air pollution exposure is expected to double by 2050 and is widely accepted as a notable risk factor for increasing morbidity.
The study analysed semen parameters (sperm motility, count, concentration) using samples from 33876 men, an impressively large sample size. The men for the investigation were chosen because they were pursuing assisted reproductive procedures for conception, such as in-vitro fertilisation (IVF).
In the end, an association between exposure to PM and reduced sperm motility was found, but no significant effect on sperm count and concentration.
Upon evaluation of PM size, the study found that exposure to fine PM during sperm development had the greatest effect on motility, wherein it reduced it significantly, compared to medium and large PM. Interestingly, they also found an effect between the timing of PM exposure during sperm development and motility; if exposure occurred during earlier stages of development, there was a larger impact on motility.
A suggested reason for this relationship was that early exposure to PM could affect the expression of important genes during this development stage. Genes are essentially the instruction manual or ‘recipe’ for creating everything that goes on in and around our bodies, everything from eye colour to hormones to cell development.
The study was limited because it did not account for other environmental changes that may affect sperm quality, such as obesity and smoking. Regardless, the evidence put forward is alarming.
Studies such as this show why reducing the impact of air pollution on sperm quality via public health interventions and individual efforts is a necessity.
Find out more about future attempts to combat climate change in our coverage of Earth Day, 2021
