Biology

Dramatic decline in Western sperm counts over past 40 years

Dramatic decline in Western sp...
A large-scale meta-analysis of 185 studies across 40 years has found total sperm count among men in the West is in decline
A large-scale meta-analysis of 185 studies across 40 years has found total sperm count among men in the West is in decline
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The downward trend found in the large meta-analysis of global sperm counts
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The downward trend found in the large meta-analysis of global sperm counts
A large-scale meta-analysis of 185 studies across 40 years has found total sperm count among men in the West is in decline
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A large-scale meta-analysis of 185 studies across 40 years has found total sperm count among men in the West is in decline

A large-scale meta-analysis of 185 studies across 40 years has found a more than 50 percent decline in sperm concentration and total sperm count among men from North America, Europe, Australia and New Zealand. The rate of decline was found to be consistent and is cause for significant concern if the trend continues.

Previous studies showing downward trends in global sperm counts have been criticized by scientists for a variety of factors. It has been argued that many prior fertility studies contained data that was skewed by selection bias and weren't representative of the broader population. Other researchers have also questioned the validity of historical sperm count estimates, claiming older studies were unreliable due to inaccurate measuring techniques.

This latest study attempts to correct for these limitations. Unlike earlier meta-analyses that included sample counts going as far back as 1931, this study only included data collected since 1973 so as to reduce the uncertainty in its results. Meta-regression models were also developed to account for variable factors such as age, abstinence and selection of the study population.

The results were ultimately collated from 42,935 men split into two geographic groups: Western (including North America, Europe, Australia and New Zealand) and Other (including South America, Asia and Africa).

A frighteningly steep decline was seen in both total sperm count and sperm concentration across men in Western countries. A similar trend was not seen in other geographic groups, but the researchers note that there was limited statistical data to be gathered from non-Western countries.

The downward trend found in the large meta-analysis of global sperm counts
The downward trend found in the large meta-analysis of global sperm counts

"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," says lead author on the study Dr. Hagai Levine.

The study did not look at what could be causing this steep decline, but the researchers suspect that, "endocrine disruption from chemical exposures or maternal smoking during critical windows of male reproductive development may play a role in prenatal life, while life-style changes and exposure to pesticides may play a role in adult life."

Despite the frightening implications of this study it is important to understand the limitations of the data. While the sperm count downward trend is undeniable, it is not necessarily a clear indication of fertility as the study didn't take into account motility of the sperm.

The overall numbers also don't indicate significant increasing infertility in Western men. The study tracked a 53.4 percent drop in Western male sperm concentration, down from 99 million per milliliter in 1973 to 47 million per milliliter in 2011. Current World Health Organization standards state that any volume over 15 million sperm per milliliter is considered normal.

So while hyperbolic "human extinction" claims are swirling, we are not yet heading toward some dystopian fertility crisis à la The Handmaid's Tale or Children Of Men. Rather, this may be a sign of a greater environmental impact on male health. As the researchers note in the conclusion of the study, let this serve as a "canary in the coal mine" that signals broader issues could be at play.

The study was published in Human Reproduction Update.

Source: Hebrew University of Jerusalem via Eurekalert

15 comments
15 comments
jordan
With overpopulation the way it is, might just be a literal safe guard built into our DNA.
SamB
Modern life is neutering us
El Bonko
@jordan That's not how DNA works. And there's no overpopulation in the West (or, arguably, anywhere). This is more likely due to a foreign substance introduced into our precious bodily fluids.
kid-jensen
" there is no overpopulation in the West (or, arguably, anywhere)",
Really?
Tell that the the commuter on the Northern line...
Why are we devastating so much land to feed and house our population if it's not increasing?
Brian M
Even a level of well below 15 million does not imply infertility either.
However if there is a decline then there will be a reason, whether its in the way the participants are chosen, remembering there will be both social and religious reasons of why the samples might not be representative of the population.
Later studies might be more representative, so maybe the real norm is a lower?
There is of course the worrying probability that pollution or life styles is the cause. But low sperm count can often be improved dramatically in months by simply improving diet (fruit etc.) and other life style changes, including, and surprisingly, less rigorous exercise!
So don't panic (just) yet!
Brian M
@El Bonko
Actual how genes are expressed can be altered by changes in environment and not just DNA - its like a short term change to how the 'DNA' is used, which from a survival perspective makes sense.
If our bodies picked up something that hinted at overpopulation, then its not impossible its a response. For example a lot of estrogen in the environment might be indicative of overpopulation, so the mechanism kicks in to slowly reduce population rather than a crash.
Above just a possible mechanism - not saying it is!
As for overpopulation, its a matter of definition, but a population that can't healthily sustain itself or with a population dense enough to allow disease to run through it without a 'fire' break is an overpopulation!
London easily makes that definition, as do many other cities!
Bob
Another change that needs looking in to is the number of young men losing their hair prematurely. Among my 65-70 year old friends about half of us still have a fairly full head of hair but among our sons most are going bald in their 20s and 30s. Worse yet, the trend seems to be accelerating with the younger ones showing markedly thinning hair right out of college. This was rare 50 years ago but is quite common now. What other effects are we going to see as time goes on. Another interesting thing is diet. Many of the people I know that grew up eating bacon, greasy sausage, real butter, and eggs are living into their late 80s to early 90s. Those of us that are 20 years younger and grew up in the fast food era aren't fairing so well. About a third of my high school class mates were already dead at our 50th reunion and another third in badly failing health. The average lifespan will soon be dropping at a rapid rate. Even with medical advances, science and the proliferation of chemicals is killing us.
SammyC
We're still arguing that the west is over populated huh? Look at the birth rates compared to the replacement fertility rates. In short you need about 2.1 kids per man/woman just to maintain the population. The west is way below that as is Japan and a bunch of other places.. There's a ton of really smart and educated comments in New Atlas articles - the ones crying about over pop are not those. Spend just a few minutes doing some research - population numbers are not the problem. I just read an article a few weeks ago that tried to make the case that Venezuela's population was the reason for all their shortages and crime. It'd be funny if it wasn't so sad..
Douglas Bennett Rogers
This trend precisely matches the "chickafication" of the West and Japan. The brain has a powerful effect on the body.
Pablo
One word: Chemtrails...
Seriously, our western diet, prescription and "other" drug consumption, built environment, and stress are all factors we should study.