Alan Cassels is a drug policy researcher at the University of Victoria and a regular contributor to the blog. He is also the author, most recently, of The Cochrane Collaboration: Medicine’s Best-Kept Secret. He tweets as @AKEcassels.
Last week headline writers seized upon a study looking at falling sperm counts in men.
“Sperm count drop ‘could make humans extinct,’” a BBC news article warned. Quartz explained that “Most men in the US and Europe could be infertile by 2060′ and CNN let us know that “Sperm counts in Western Men Plummeting, Analysis Finds.”
Environmental Health News added to the hype with its headline — “Are we in a male fertility death spiral?” — and a photo caption that stated: “Male impotency is a growing problem. Here’s why you should be worried—and your kids should be terrified.”
Death spiral? Extinct humans? Terrified kids? Wow, this is some heavy-duty fear-mongering. Was it warranted?
First, the facts: The headlines all draw from a meta-analysis published in the journal Human Reproduction Update. After looking at about 185 studies involving 42,000 men mostly from Western nations, researchers found sperm concentrations decreased about 52% and total sperm counts specifically decreased about 59% from 1973 to 2011.
For some perspective, I talked to Chris Barratt, MD, a professor of reproductive medicine, at the University of Dundee in Scotland, who wrote that over-the-top piece for Quartz. I wanted to know how he could he explain his conclusion, captured in the headline, where he said: “Most men in the U.S. and Europe could be infertile by 2060.”
He says the comment comes from extrapolating the current data found in the meta-analysis “to its logical conclusion.”
“If you look at the slope of the line in the paper, what you see is that it’s a strong slope–similar to what you see with female fertility with age,” he said.
But is that a fair comparison? Decreasing female fertility across the lifespan is a very well documented phenomenon and an established element of human biology. Falling sperm counts among the entire male population, by contrast, have been documented for only about 40 of the 200,000 years that homo sapiens has been walking the earth (evidently with enough viable sperm to keep the race going).
Given this impressive stretch of reproductive success, is it really “logical” to conclude that a 40-year dip might portend widespread male infertility?
Moreover, as Ars Technica pointed out in a well-written piece, the most recent numbers–while lower than the 1970s– are still within normal ranges.
In other words, the sperm count average has gone from “normal” to, well, “normal.”
Still, Barratt couldn’t control his astonishment: “I found this amazing,” he said, “that the significant reduction in the reproductive capacity is on a line that keeps going down.”
This, however, is not the end of the world’s male reproductive capacity. The data, he reminds me, “is very incomplete,” where only 16% of the subjects in the study came from poorer countries in South America and parts of Africa. “We don’t have a lot of data from China, Russia and India.”
He also added that you need to look closely at the men included in the study, that is, men whose partners have conceived in the last 18 months or so (and thus clearly been fertile enough to father children naturally), which creates a different picture.
“If you look at fertile men,” he said, “there doesn’t seem to be such a decrease.” This is relevant because much of the previous research was overrepresented with men who may be attending a fertility clinic, whose low sperm counts are not reflective of the rest of the male population.
As for the Big Question: Why is this happening? Unfortunately, it’s mostly speculation–environmental toxins and poor lifestyle choices both getting mentioned as contributors that are hard to study as direct causes.
“The main theory is that the effect is primarily taking place in the fetal testes,” Barratt said. “There is a change in the environment in fetal testes–which are modulators of function.”
There is “evidence to support this” he said, citing a significant rise in the rates of testicular cancer, but the phenomenon is arguably difficult to test.
“We don’t really understand what causes it. People worry about the environmental issues–but demonstrating them is impossible,” he said. And while there are “animal studies’, for example, looking at endocrine disruptors, those studies, he suggests are “problematic.”
But back to this study, Barratt adds that “to say men are going to be wiped off the face of the earth is probably an exaggeration.”
Let’s not forget why this is such an important story for news consumers. It addresses an issue of great interest to the many couples who desperately want a baby and are struggling to conceive.
The Sun in the UK gave a helpful, if cheeky, primer on the things you should do to preserve male fertility: “Don’t drink too much, don’t use steroids, and whatever you do, don’t “cook your balls.”
NPR’s take felt a bit more practical, stressing that age is a big factor in fertility rates and that couples should consider trying to conceive earlier.
NPR’s other big takeaway came from a researcher, Allan Pacey, PhD, a professor of Andrology at the University of Sheffield. He says that the results should be taken seriously but warns against media reports of a “spermapocalypse.”
“There’s a real danger here that researchers publish papers like this, that are then reported irresponsibly, that then lead to people getting really paranoid about what may or may not be happening,” Pacey says.