Sperm counts haven't declined in recent years, but motility has

Research into sperm donors in Denmark shows no evidence of a decline in sperm counts in recent years, but it does reveal a significant decrease in sperm motility.

Researchers analysed the sperm quality of men applying to be sperm donors at the Cryos sperm bank in four Danish cities between 2017 and 2022. While they found a significant decline in sperm motility (how fast and efficiently sperm are moving), sperm concentration and count remained stable. This contrasts with a recent study indicating a decline in sperm counts over the last 50 years (see BioNews 1168).

'It is commonly believed that sperm counts in men are falling. This is to some degree the result of a meta-analysis published by Levine et al. (2023) which proposed that sperm concentrations worldwide had declined as much as 2.64 percent per year in unselected men since the year 2000,' said co-author Professor Allan Pacey, professor of andrology at the University of Manchester and trustee of PET (the Progress Educational Trust) which publishes BioNews. 'We did not see such a change and that suggests that in this population of sperm donor applicants, in these four Danish cities, sperm concentrations have not changed between 2017 and 2022.'

The study published in Human Reproduction included 6758 donor candidates aged between 18 and 45 years. Although the average sperm concentration fluctuated from year-to-year, there was no significant change over the six-year period. However, levels of sperm motility decreased significantly between 2019 and 2022. The average motile sperm concentration of donor applicants declined by 16 percent from 18.4 million/ml in 2019 to 15.5 million/ml in 2022, while the total motile sperm count declined by 22 percent from 61.4 million per ejaculate to 48.1 million.

This trend was confirmed when the researchers examined 77,561 ejaculates from 1839 donors who were accepted onto the Cryos sperm bank donation programme and donated regularly between 2017–2022. In this subpopulation, the total motile sperm count declined by 21 percent from 2019 to 2022. The researchers suggested that the COVID-19 pandemic and associated lifestyle changes might be a cause for the observed decline in sperm motility.

These donors had been asked to refrain from donating within 30 days of experiencing symptoms or a diagnosis of COVID-19, and authors proposed it was therefore unlikely the decline was due to exposure to the SARS-CoV-2 virus.

The researchers propose that monitoring men applying to be sperm donors will provide valuable insights into changes in human semen quality over time, helping to identify external factors contributing to any decline in sperm quality.