Men's sperm counts have more than halved over the past 50 years, with potentially drastic consequences for the future of the human race.
About one in six adults worldwide experience infertility at some point, according to the World Health Organization, and between 30% and 50% of cases are linked to problems with the quantity and quality of semen, said New Scientist. Either the total number of sperm is too low, or the cells "struggle to swim" (reduced motility), which decreases the chance of reaching an egg cell.
The big question is no longer "whether this so-called 'spermageddon' is happening", said science writer David Robson, "but why, and what to do about it".
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What is 'spermageddon'?
The "drastic shift" in sperm counts has been documented since the 1970s, but by the 1990s "the issue started catching considerably more scientific attention", said Robson.
In 2017, veteran reproductive epidemiologist Shanna Swan and her team at the Icahn School of Medicine at Mount Sinai, New York, published a meta-analysis of 185 studies of more than 42,000 men between 1973 and 2011: "the largest of its kind", said Robson.
The results showed that the concentration of sperm in a millilitre of semen, and the total number of sperm in the sample, seemed to have decreased by 50%-60% in men from North America, Europe and Australasia. "If the decline continued at this rate, the median sperm count would reach zero by the mid-2040s," said Robson.
The team followed up with new data from South America, Asia and Africa in 2022, controlling for potential reporting bias and changing technology, and reported a decline on every continent.
The decline, they warned, had the potential to "threaten mankind's survival", said The Times.
Why is this happening?
"Various features of modern life have been posited as potential causes," said Forbes, including pollution, alcohol and drug use, increasing temperatures due to global warming, stress, poor diet, sedentary lifestyle and exposure to chemicals like pesticides.
Swan's team particularly highlighted pollutants called endocrine-disrupting chemicals, or EDCs, found in some plastics and pesticides.
Other studies found a link between obesity and a lower sperm count with reduced sperm motility. Excess body fat could cause inflammation that disturbs the hormonal balance necessary to produce sperm, Albert Salas-Huetos, a researcher at the University of Rovira i Virgili in Spain, suggested.
One eye-catching study, published in the Fertility and Sterility journal last year, found "significant exposure-response trends" between decreased sperm count and concentration, and "increasing frequency of mobile phone use". Men between the ages of 18 and 22 who said they used their phones more than 20 times a day had a 21% higher risk of a low overall sperm count, said CNN.
Nutrition could also be a factor, with one 2019 study finding that men who regularly consumed fruit, vegetables, nuts and fish had higher sperm concentrations, with greater motility, compared with those with less balanced diets.
Viruses are increasingly under the microscope, with a study in 2022 finding that Covid-19 infections reduced sperm counts and motility.
Interestingly, however, one study that analysed data measuring the sperm of dogs, between 1988 and 2014, found a comparable decline to humans.
What are the potential consequences?
It isn't yet clear how important a decline in sperm is for "overall fecundity", said Robson. Despite "large variation" in sperm count among healthy men, "the absolute figures don't seem to make a big difference to the chances of conception until they dip below a very low threshold".
But much of the chemical pollution that harms fertility is also leading to more babies being born with reproductive disorders, according to Swan. It increases the likelihood of undescended testes, genital malformations and smaller penises. There is also a link between reduced sperm counts and rising rates of testicular cancer among young men.
The good news, said Euronews, is that at least some of the damage is reversible – "provided we take action". Healthy, balanced diets, weight loss and quitting smoking can all lead to increased sperm counts.
