Something weird is going on with human sperm production. For decades, scientists have warned that sperm counts are dropping among Western men, but no one has really been able to prove it. In what is now the largest and most comprehensive study of its kind, scientists have presented compelling evidence in support of this rather alarming assertion, showing that sperm counts have dropped more than 50 per cent in just four decades.
The sperm count decline is real and it's not showing any signs of slowing down, according to new research published in Human Reproduction Update. By conducting a meta-analysis of 185 studies published between 1973 and 2011, researchers from the Hebrew University-Hadassah Braun School of Public Health and Community Medicine and the Icahn School of Medicine at Mount Sinai documented a 52.4 per cent decline in sperm concentration, and a 59.3 per cent decline in total sperm count among men living in North America, Europe, Australia, and New Zealand. The same declines were not observed among men living in South America, Asia, and Africa, where fewer studies have been performed.
Both total sperm counts and sperm concentration (i.e. the total number of sperm in a given volume) are good measures of male reproductive ability. The men used in these studies weren't chosen because of any suspected fertility issues. Alarmingly, the rate of decline does not appear to be stopping; the downward slope was "steep and significant" even when the meta-analysis was restricted to studies done after 1995.
Image: Levine et al., 2017
"Given the importance of sperm counts for male fertility and human health, this study is an urgent wake-up call for researchers and health authorities around the world to investigate the causes of the sharp ongoing drop in sperm count, with the goal of prevention," said study lead author Hagai Levine in a statement.
Low sperm counts are often an indicator of other health problems, and are often used by doctors to predict health and morbidity. Reduced sperm is thought to be the result of environmental influences, including exposure to noxious chemicals while in the womb, exposure to pesticides, and lifestyle factors such as smoking, obesity, and stress. Not surprisingly, low sperm counts are also associated with reduced fertility.
Scientists began to notice that something was amiss with human sperm counts back in 1992, but the issue remained controversial due to unconvincing research.
"Previous studies used smaller sample sizes, whereas our study was three times as large as [the one done back] in 1992," explained Levine and his co-author Shanna H. Swan in an email to Gizmodo. "This enabled us to reliably measure and assess trends in subgroups."
Other problems with the earlier research included poor or insufficient screening criteria, lack of quality control, and limited statistical methods -- all of which were addressed in the new study, according to the researchers.
"We developed a very detailed protocol, all our selected studies were examined by two researchers independently, we had a strict quality control process, and we used state-of-the-art meta-regression methods not available in 1992," said Levine and Swan.
For the new analysis, the researchers pored through the existing body of research to evaluate the reliability of study estimates, and controls for factors that might explain the decline such as age, abstinence time, and selection of the study population. By doing so, the researchers were able to confirm what has been suspected for quite some time now.
"Decreasing sperm count has been of great concern since it was first reported twenty-five years ago. This definitive study shows, for the first time, that this decline is strong and continuing," said Swan. "The fact that the decline is seen in Western countries strongly suggests that chemicals in commerce are playing a causal role in this trend."
But, that last part's just speculation. Scientists don't actually know what's causing the sperm count crisis, but this study suggests the Western lifestyle may have something to do with it. Levine and Swan recommend that future analyses take a similar approach to their own and investigate parts of the world not covered in this latest analysis.
"Studies should also look at environmental and lifestyle factors (such as chemical exposure, stress, and smoking), and semen quality," Levine and Swan told Gizmodo. "Investments should also be made into studying male reproduction."
Are we heading towards a Handmaid's Tale world of low fertility? Probably not, but the new research is alarming.
And indeed, the impact of low sperm counts on male fertility should be of great concern. The researchers say the reported declines in sperm production have manifested in the general population, and that "more couples are infertile," adding that "From statistical point of view, such a large decline must implicate [a] larger proportion of infertile and subfertile men."
We're nowhere near a fertility crisis at the moment, so fears of us entering into a Handmaid's Tale world are largely overstated. Sure, the data shows an ongoing downward trend, but that's no guarantee it will continue into the future. For all we know we've hit (or will soon hit) a wall in terms of low sperm counts). But that has yet to be proven, and this research is admittedly scary. And for the growing number of couple who can't conceive, this is already a serious problem.