A striking meta-study published in 2017 reported a 50% decline in the average male sperm count since the 1970s. A newly published follow-up investigation, including more data from more countries, is suggesting that decline in sperm counts may be accelerating. But not all reproductive researchers are convinced the data is as clear as it seems.
The new research expands on the earlier findings, adding more recent data from a diverse set of countries, this time including studies looking at sperm counts in South and Central America, Asia and Africa. The new conclusions indicate the decline in sperm counts previously seen in North America, Europe and Australia are being mirrored in countries all across the world.
Alongside that, the new research suggests the rate of decline has accelerated since the turn of millennium. Extra data included here, covering a period spanning 2011 to 2018, revealed the rate of decline has doubled since 2000.
"Our findings serve as a canary in a coal mine," said Hagai Levine, lead researcher on the project. "We have a serious problem on our hands that, if not mitigated, could threaten humankind's survival. We urgently call for global action to promoted healthier environments for all species and reduce exposures and behaviors that threaten our reproductive health."
As with the team's 2017 findings, the conclusion does not arrive without controversy. Several reproductive researchers have long argued these kinds of longitudinal meta-analyses tracking sperm counts across different studies are not accurate ways of evaluating changes over time.
A debate article published last year in the journal Fertility and Sterility summed up the argument against these kinds of meta-studies, claiming semen analysis techniques are profoundly variable, with no standardization between labs and improvements occurring over time. Allan Pacey, a professor of andrology from the University of Sheffield, is skeptical of these big sperm count meta-studies.
“Counting sperm, even with the gold standard technique of haemocytometry, is really difficult," Pacey said. "I believe that over time we have simply got better at it because of the development of training and quality control programs around the world. I still think this is much of what we are seeing in the data."
Other researchers have argued the big, sweeping long-term declines being detected in studies such as Levine's are not replicated in smaller, more focused investigations of singular populations. This suggests the larger meta-studies may not be accurate representations of what is actually going on.
For example, a study tracking semen quality in Copenhagen men over 15 years between 1996 and 2010 actually found sperm counts increased over time. A similar Canadian study looked at 12 years of data from 1984 to 1996 and found no change in sperm count over time.
But not everyone is skeptical of these new findings. Sarah Martins da Silva, a reproductive medicine expert from the University of Dundee, is not convinced the differences in sperm counting techniques over time are relevant here. She believes the new study is robust in its accounting for variables in the data and the results are too consistent to ignore.
“The conclusion is that sperm counts are falling," da Silva said. "The human race is not at immediate risk of extinction but we really need research to understand why sperm counts are falling and to prevent other unintended implications for male health.”
It is important to note that the reported rate of decline in sperm counts has not reached a level that would significantly affect fertility for most people. The new research estimates the median sperm concentration in men right now is still around 40 million per milliliter.
The World Health Organization's current standards indicate any volume over 15 million sperm per milliliter is considered normal. And, there are plenty of other factors beyond simple sperm concentration that can play a role in male fertility, particularly sperm motility.
Richard Sharpe, a reproductive health specialist at the University of Edinburgh, said the most crucial takeaway from this new study is what it could mean for older couples in their 30s or early 40s looking to conceive. According to Sharpe, because many couples in Western countries are having children at later ages, a drop in male sperm count could make it substantially harder to conceive.
"If her male partner has a low sperm count (and the present data shows that this is increasingly likely)," Sharpe explained, "then we know from prospective couple studies that the chances of him impregnating his partner are reduced – he may be able to get her pregnant but it will take longer and time is not on their side (because of the progressive decline in the female partners fertility as she ages); and the lower his sperm count the longer it will take. As I term it a perfect recipe for increased couple infertility!"
Setting aside the fertility implications of this kind of global decline in sperm count, co-author on the new study Shanna Swan notes the findings could have general implications for men's health. Swan, from the Mount Sinai Icahn School of Medicine in New York, said low sperm counts have been correlated with a number of adverse health problems in men. So if there is indeed a general trend to lowered sperm counts then it could be an early sign of health problems that have yet to significantly rear their head.
"The troubling declines in men's sperm concentration and total sperm counts at over 1% each year as reported in our paper are consistent with adverse trends in other men's health outcomes, such as testicular cancer, hormonal disruption, and genital birth defects, as well as declines in female reproductive health," Swan added. "This clearly cannot continue unchecked."
The new study was published in the journal Human Reproduction Update.
Source: Hebrew University of Jerusalem
