- A new review of a famous study on declining sperm counts finds several flaws.
- The old report makes unfounded assumptions, has faulty data, and tends toward panic.
- The new report does not rule out that sperm counts are going down, only that this could be quite normal.
Several years ago, a meta-analysis of studies on human fertility came out warning us about the declining sperm counts of Western men. It was widely shared, and its findings were featured on the covers of popular magazines. Indeed, its findings were alarming: a nearly 60 percent decline in sperm per milliliter since 1973 with no end in sight. It was only a matter of time, the authors argued, until men were firing blanks, literally.
Well… never mind.
It turns out that the impending demise of humanity was greatly exaggerated. As the predicted infertility wave crashed upon us, there was neither a great rush of men to fertility clinics nor a sudden dearth of new babies. The only discussions about population decline focus on urbanization and the fact that people choose not to have kids rather than not being able to have them.
Now, a new analysis of the 2017 study says that lower sperm counts is nothing to be surprised by. Published in Human Fertility, its authors point to flaws in the original paper’s data and interpretation. They suggest a better and smarter reanalysis.
Counting tiny things is difficult
The original 2017 report analyzed 185 studies on 43,000 men and their reproductive health. Its findings were clear: “a significant decline in sperm counts… between 1973 and 2011, driven by a 50-60 percent decline among men unselected by fertility from North America, Europe, Australia and New Zealand.”
However, the new analysis points out flaws in the data. As many as a third of the men in the studies were of unknown age, an important factor in reproductive health. In 45 percent of cases, the year of the sample collection was unknown — a big detail to miss in a study measuring change over time. The quality controls and conditions for sample collection and analysis vary widely from study to study, which likely influenced the measured sperm counts in the samples.
Another study from 2013 also points out that the methods for determining sperm count were only standardized in the 1980s, which occurred after some of the data points were collected for the original study. It is entirely possible that the early studies gave inaccurately high sperm counts.
This is not to say that the 2017 paper is entirely useless; it had a much more rigorous methodology than previous studies on the subject, which also claimed to identify a decline in sperm counts. However, the original study had more problems.
Garbage in, garbage out
Predictable as always, the media went crazy. Discussions of the decline of masculinity took off, both in mainstream and less-than-reputable forums; concerns about the imagined feminizing traits of soy products continued to increase; and the authors of the original study were called upon to discuss the findings themselves in a number of articles.
However, as this new review points out, some of the findings of that meta-analysis are debatable at best. For example, the 2017 report suggests that “declining mean [sperm count] implies that an increasing proportion of men have sperm counts below any given threshold for sub-fertility or infertility,” despite little empirical evidence that this is the case.
The WHO offers a large range for what it considers to be a healthy sperm count, from 15 to 250 million sperm per milliliter. The benefits to fertility above a count of 40 million are seen as minimal, and the original study found a mean sperm concentration of 47 million sperm per milliliter.
Healthy sperm, healthy man?
The claim that sperm count is evidence of larger health problems is also scrutinized in this new article. While it is true that many major health problems can impact reproductive health, there is little evidence that it is the “canary in the coal mine” for overall well-being. A number of studies suggest that any relation between lifestyle choices and this part of reproductive health is limited at best.
Lastly, ideas that environmental factors could be at play have been debunked since 2017. While the original paper considered the idea that pollutants, especially from plastics, could be at fault, it is now known that this kind of pollution is worse in the parts of the world that the original paper observed higher sperm counts in (i.e., non-Western nations).
There never was a male fertility crisis
The authors of the new review do not deny that some measurements are showing lower sperm counts, but they do question the claim that this is catastrophic or part of a larger pathological issue. They propose a new interpretation of the data. Dubbed the “Sperm Count Biovariability hypothesis,” it is summarized as:
“Sperm count varies within a wide range, much of which can be considered non-pathological and species-typical. Above a critical threshold, more is not necessarily an indicator of better health or higher probability of fertility relative to less. Sperm count varies across bodies, ecologies, and time periods. Knowledge about the relationship between individual and population sperm count and life-historical and ecological factors is critical to interpreting trends in average sperm counts and their relationships to human health and fertility.”
Still, the authors note that lower sperm counts “could decline due to negative environmental exposures, or that this may carry implications for men’s health and fertility.”
However, they disagree that the decline in absolute sperm count is necessarily a bad sign for men’s health and fertility. We aren’t at civilization ending catastrophe just yet.