People could face a reproductive crisis if steps aren’t taken to combat a drop in sperm count, researchers have warned after finding the rate of decline is accelerating.
A study published in the journal Human Reproduction Update, based on 153 estimates from men who were likely unaware of their fertility, suggests that between 1973 and 2018, the average sperm concentration increased from an estimated 101.2 m per ml to 49.0 m per ml has decreased – a decrease of 51.6%. Total sperm count fell by 62.3% over the same period.
Research by the same team, reported in 2017, found sperm concentrations had more than halved in the past 40 years. However, at the time, a lack of data for other parts of the world meant the results were concentrated in a region that included Europe, North America and Australia. The latest study includes more recent data from 53 countries.
Decreases in sperm concentration were observed not only in the previously studied region but also in Central and South America, Africa and Asia.
In addition, the rate of decline appears to be increasing: looking at data collected on every continent since 1972, the researchers found that sperm concentrations were declining by 1.16% per year. However, if they only looked at data collected since 2000, the decline was 2.64% per year.
“I think this is another signal that something is wrong with the globe and we need to do something about it. So yeah, I think it’s a crisis that we [had] better act now, before it reaches a tipping point that may be irreversible,” said Prof Hagai Levine, first author of the study from the Hebrew University of Jerusalem.
Previous studies have shown that fertility is impaired when sperm concentration falls below about 40 µM per ml. While the most recent estimate is above that threshold, Levine noted that this is a mid-range number, suggesting that the percentage of men below that threshold will have increased.
“Such a decline clearly represents a decline in the reproductive capacity of the population,” he said.
While the study took into account factors such as age and how long men had been without ejaculation, and excluded men known to have infertility, it has limitations, including the fact that other markers of sperm quality were not considered.
Allan Pacey, a professor of andrology at the University of Sheffield, who was not involved in the work, praised the analysis but said he remained on the fence about whether there was a drop.
“Count sperm, even with the gold standard technique of [the laboratory process] Haemocytometry, it’s really difficult,” he said. “I think we’ve just gotten better at it over time due to the development of training and quality control programs around the world. I still think that’s a lot of what we’re seeing in the data.”
However, Levine dismissed such concerns, adding that the decline has definitely been stronger in recent years.
Although it is unclear what might be behind the apparent trend, one hypothesis is that endocrine disrupting chemicals or other environmental factors may play a role and affect the fetus in utero. Experts say factors like smoking, drinking, obesity and poor diet could also play a role, and that a healthy lifestyle can help increase sperm count.
Tina Kold Jensen from the University of Southern Denmark said the new study recaps a worrying trend. “You always find the same trend no matter how many studies you look at — it’s a bit scary to me,” she said.
Prof Richard Sharpe, male reproductive health expert at the University of Edinburgh, said the new data showed the trend appears to be a global phenomenon.
Sharpe said the drop could mean couples are taking longer to conceive and for many time is not on their side as they delay trying to conceive until the woman is in her 30s or 40s if their fertility is already reduced.
“The key point that needs to be made is that this is desperately bad news for couples’ fertility,” he said.
But, Sharpe said, “These problems aren’t just a problem for couples trying to have children. They are also a major problem for society over the next 50 years or so, as fewer and fewer young people will be working and supporting the growing number of older people.”