Just keep swimming

Emerging science debunks the myth of falling sperm counts

“Fertility is an extremely complex phenomenon that is affected by a whole range of other factors beyond sperm count.”

Human sperm cells

Sperm — or more accurately, the lack thereof — has seeped into the American consciousness and people are worried (although perhaps not for the reason you might think).

The sperm count of men in Western countries is, so the story goes, in decline — perhaps irrevocably. The prostate panic truly kicked off in 2017, when a Newsweek cover asked: “Who’s Killing America’s Sperm?” That story, and much of the ensuing dialogue around men, fertility, and sperm counts, was based on a research analysis that estimated changes in the global sperm count over time.

The analysis was published in Human Reproduction Update, and it concluded that sperm counts are falling — specifically among men in the West. One of the authors of the 2017 analysis even went on to publish a book on the subject, CountDown. But a fresh look at the data, published earlier this year in the journal Human Fertility, questions the theory that sperm counts are in decline.

What they discovered — The new analysis also found that sperm count has declined, but the drop is within the “normal” range. And perhaps more importantly for men worried about their fertility, scientists don’t actually know what the connection between sperm count and fertility looks like. So the authors of the fresh analysis offer a new way to think about the dip — the Sperm Count Biovariability hypothesis.

Marion Boulicault, one of the authors of the new paper, tells Inverse that the hypothesis hinges on a couple of crucial points:

  • First, it “encourages scientists to begin with an open mind to the idea that sperm count can vary.”
  • Second, that sperm count can vary “within a wide wide range.”
  • Third, that “many of the changes in sperm count might be non-pathological and species-typical.”

What is true is that there is a great range in “typical” sperm count in males, and this is one of the reasons Boulicault thinks the fear around declining sperm count is overblown. According to the Mayo Clinic, “normal sperm densities range from 15 million to greater than 200 million sperm per milliliter of semen.” Low sperm count equates to “fewer than 15 million sperm per milliliter or less than 39 million sperm total per ejaculate,” according to that resource.

Are sperm counts in decline?

Rene Almeling is an associate professor of sociology at Yale University and author of GUYnecology: The Missing Science of Men's Reproductive Health. She tells Inverse that we should be highly skeptical of conclusions based on average sperm counts. While some studies indicate a decline in sperm count over the past 50 years, it’s extremely difficult to know how scientifically sound those studies are.

“There is a long history of inattention to men’s reproductive health, especially when compared to women’s reproductive health,” she says. “As a result, scientists cannot say with certainty what ‘average’ sperm counts were in the past or are even now in the present.”

What is healthy sperm?

The question over what is “healthy” when it comes to sperm gets to the heart of one of the issues with the 2017’s paper’s hypothesis, Boulicault says. Healthy sperm and sperm count aren’t the same things. Sperm count is just one of several factors doctors assess to determine the health of sperm. According to Boulicault, doctors also consider the following:

  • Sperm mobility — i.e., how fast or efficiently they can swim
  • Sperm morphology — i.e., the shape of sperm
  • Ejaculate volume — no explanation needed, we hope

For anyone worried about the health of their sperm, there are things you can do to boost your swimmers’ overall wellbeing and perhaps increase your sperm count, too.

3d rendering of sperm cells

Shutterstock/White Markers

How to increase sperm count

It’s important to remember two things before we get into these recommendations:

  • Sperm count isn’t the only factor that matters for fertility
  • Nothing is a guarantee

There are four science-backed strategies anyone can take to increase the health of one’s sperm and boost sperm count, too. In no particular order, these methods include:

  • Diet A healthy diet replete with Omega-3 fatty acids like those found in oily fish and nuts.
  • Regular exercise Many studies show that exercise boosts both sperm count and sperm mobility. Be careful not to overdo it, though, as other studies suggest that too much exercise can have the opposite effect.
  • Vitamins and minerals Zinc, Vitamin D, and Vitamin C have all been shown to have a positive effect on sperm, though it’s important to note that in the case of Vitamin D, the benefits may only extend to people who are deficient in the vitamin.
  • Stress Stress is bad for the body, and for men, sperm is no exception. Anything you can do to reduce your stress levels will help your sperm live their best, albeit extremely short, life.

How sperm count affects fertility

As of now, we don’t really know how sperm count and fertility relate to one another, Boulicault says.

“At the extreme, we know with 100 percent certainty that if somebody has a sperm count of zero, then they are infertile,” she says. “So it’s definitely related. But we also know that sperm count alone, aside from this kind of extreme, is a very poor predictor of fertility.”

“Fertility is an extremely complex phenomenon that is affected by a whole range of other factors beyond sperm count,” she adds.

Almeling agrees. She says that there’s a high degree of uncertainty about the “precise relationship between an individual man’s sperm count and his fertility.” The best thing any man can do is to look after their body — and by extension — their sperm.

Boulicault says it is positive that male fertility is gaining more scientific interest. But she cautions against getting too wrapped up in sensationalized headlines based on current research.

“As it stands, there simply isn’t enough evidence to warrant these Doomsday predictions,” she says.

Abstract: The past 50 years have seen heated debate in the reproductive sciences about global trends in human sperm count. In 2017, Levine and colleagues published the largest and most methodologically rigorous meta-regression analysis to date and reported that average total sperm concentration among men from ‘Western’ countries has decreased by 59.3% since 1973, with no sign of halting. These results reverberated in the scientific community and in public discussions about men and masculinity in the modern world, in part because of scientists’ public-facing claims about the societal implications of the decline of male fertility. We find that existing research follows a set of implicit and explicit assumptions about how to measure and interpret sperm counts, which collectively form what we term the Sperm Count Decline hypothesis (SCD). Using the study by Levine and colleagues, we identify weaknesses and inconsistencies in the SCD, and propose an alternative framework to guide research on sperm count trends: the Sperm Count Biovariability hypothesis (SCB). SCB asserts that sperm count varies within a wide range, much of which can be considered non-pathological and species-typical. 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 health and fertility.
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