Air pollution, in the form of particulate matter exposure, has been associated with reduced sperm quality.
Researchers retrospectively analysed semen samples from men whose wives had received assistive reproductive procedures, which included IVF and cyropreservation of gametes. They considered how well the sperm moved, in terms of non-moving sperm and poorly moving sperm, along with sperm count and concentrations, and correlated these with air pollution rates. They found that exposure to particulate matter of several different sizes was not associated with reduced sperm count and concentrations but was associated with reduced sperm quality.
Published in JAMA Network Open, the authors concluded: 'Our findings suggest that exposure to particulate air pollution during spermatogenesis may adversely affect semen quality, especially sperm motility, and highlight the need to reduce ambient particulate air pollution exposure in reproductive-aged men.'
The quality of the semen samples, which were collected from 31 provinces in China between 2013 and 2019, was quantified as the proportion of moving sperm and the proportion of correctly moving sperm (also known as progressive sperm). Only progressive sperm can make their way into the female reproductive tract.
Air pollution rates were characterised by rates of particulate matter in the air, with two groups of particular interest, fine particulate matter, which have a diameter of less than 2.5 micrometres, and inhalable particles, which have a diameter of less than ten micrometres.
The researchers, based at Fudan University, China and Jiao Tong University School of Medicine, China, analysed a total of 33,876 semen samples, and found that exposure to fine particulate matter in the 75th percentile was associated with a 3.6 percent reduction in moving sperm, and 1.9 percent less correctly moving sperm than those with exposure in the 25th percentile. Similarly, exposure to inhalable particle matter levels in the 75th percentile was associated with a 2.4 percent reduction in moving sperm and 1.1 percent less correctly moving sperm than those with exposure in the 25th percentile.
Exposure to particulate matter during spermatogenesis (the earliest stage of sperm development, where germ cells develop into sperm cells) was found to be correlated with significantly fewer moving sperm when compared to exposure during a later stage of semen development.
'The possibility of a link between air pollution and semen quality has been suggested in a number of studies over the years, although not all of them have agreed with this conclusion. This paper adds to the evidence base suggesting the link is real and is impressive because it uses semen quality data from over 30,000 men' said Professor Allan Pacey who is professor of andrology at the University of Sheffield and was not involved in the study.
There were limitations to the study, however, nearly half the men were overweight or obese (49.4 percent), and over a quarter were smokers (28.7 percent). Both confounders are known to reduce sperm counts. The authors stated that 'unmeasured confounders such as dietary habits, physical condition, and exposure to other environmental pollutants were possible.' and that 'Further studies are needed to determine the biological mechanisms underlying the observed associations.'