People could face a reproductive crisis if action is not taken to address the decline in sperm counts, researchers warn after finding that the decline is accelerating.
A study published in the journal Human Reproduction Update, based on 153 estimates from men who were probably unaware of their fertility, suggests that between 1973 and 2018, the average sperm concentration fell from an estimated 101.2 m per ml to 49, 0 m per ml – 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 that sperm concentration had more than halved over the past 40 years. However, due to a lack of data for other parts of the world, the findings at the time focused on a region encompassing Europe, North America and Australia. The latest study includes more recent data from 53 countries.
Decreases in sperm concentration were not only seen in the previously studied region, but also in Central and South America, Africa and Asia.
In addition, the rate of decline seems to be increasing: Looking at data collected on all continents since 1972, the researchers found that sperm concentrations were decreasing at a rate of 1.16% per year. However, when looking only at the data collected since the year 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 no longer be reversible,” said Prof. Hagai Levine, first author of the study from the Hebrew University of Jerusalem.
Previous studies have suggested that fertility is compromised when sperm concentration falls below about 40 m per ml. While the latest estimate is above this threshold, Levine noted that this is an average figure, suggesting that the percentage of men below this threshold will have increased.
“Such a decline clearly represents a decline in the population’s ability to reproduce,” he said.
While the study took into account factors such as age and how long men had gone without ejaculation, and excluded men known to suffer from infertility, it has limitations, including not looking at other markers of semen quality.
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 is a decline.
“Counting sperm, even with the gold standard technique of [the laboratory process] hemocytometry, is really hard,” he said. “I believe we’ve just gotten better at it over time through the development of training and quality control programs around the world. I still think this is a lot of what we see in the data.”
However, Levine dismissed such concerns, adding that the decline has been more pronounced in recent years at least.
While it’s unclear what’s behind the apparent trend, it’s been hypothesized that endocrine-disrupting chemicals or other environmental factors may play a role, acting on the fetus in the womb. Experts say factors such as smoking, drinking, obesity and poor nutrition may also play a role, and that a healthy lifestyle can help boost sperm count.
Tina Kold Jensen of the University of Southern Denmark said the new study recapitulated a worrying trend. “You keep finding the same trend no matter how many studies you count — I find that a little scary,” she said.
Professor Richard Sharpe, an expert in male reproductive health at the University of Edinburgh, said the new data showed the trend appeared to be a global phenomenon.
Sharpe said the decline could mean couples take longer to conceive and that for many, time is not on their side, delaying trying to conceive until the woman is in her 30s or 40s, when her fertility already reduced.
“The main point to be made is that this is desperately bad news for the couple’s fertility,” he said.
But, said Sharpe, “These problems are not just a problem for couples trying to have children. They are also a huge problem for society in the next 50 years, as there will be fewer and fewer young people to work and the increasing to support the protrusion of the elderly.”