Elena Scotti/FUSION

From pop culture to news headlines, women are constantly reminded of their biological clock‚ÄĒand¬†the notion that as¬†they age, so do their eggs. Tick tock, ladies, time to make a baby.

Rarely do we hear about the male biological clock‚ÄĒafter all, don't¬†the George Clooneys of the world supposedly¬†prove¬†that men get better with age? Last¬†month, however, a bioethicist published a provocative¬†paper in the British¬†Journal of Medical Ethics urging men to freeze their sperm¬†at¬†age 18.¬†The reasoning? Well, old sperm aren't so great, either.

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The author of the paper, Kevin R. Smith, a senior lecturer at Scotland's Abertay University, notes that "Modern genetic sequencing studies have confirmed that the sperm of older men contain a greater number of de novo germline mutations than the sperm of younger men." In other words, babies born from older sperm are more likely to suffer from genetic disorders and other problems.

Since many men in Western countries are delaying fatherhood, Smith argues that aging sperm could pose a problem in the future. Fathers in their 50s are 10 times more likely to have a child with achondroplasia (ACH), a form of dwarfism caused by mutational damage, he points out, than fathers in their 20s. Autism, bipolar disorder, intellectual disability, obesity and schizophrenia are also associated with advanced paternal age.

And so,¬†one solution‚ÄĒtheoretically, anyway‚ÄĒwould be for young men to¬†freeze their sperm for later use. Perhaps, Smith suggests, governments¬†could even provide universal sperm banking. (Yes, take¬†a moment to visualize that one.) But is this proposal pure science-fiction fantasy, or could we see a trend toward it in our lifetime? We posed those questions to fertility experts in the U.S., and here's what they told us.

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What does it mean to have 'old sperm'? 

While evidence is mounting that advanced paternal age may play some role in genetic disorders, it's unclear why, since sperm doesn't really age the way a woman's eggs do.

"The female body is like a warehouse," explained Scott Brown, director of communications for California Cryobank, which provides sperm freezing services. "The most amount of eggs a woman has is when she's in the womb. When she starts to menstruate, she's already lost half the eggs, and the older she gets the more they degenerate." The male body, meanwhile, "is more like a factory. It's creating more sperm now and forever."

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Indeed, the sperm in a man's body at any given time is no more than three months old, said Lawrence Werlin, a reproductive endocrinology and infertility specialist who founded Coastal Fertility Medical Center in California.

"Men's sperm run a lifecycle of 74 to 90 days," he explained, referring to the sperm regeneration cycle, or the time it takes sperm cells to mature inside the testes. Thus, both a 45-year-old man and a 20-year-old man have three-month-old sperm.

Yet when it comes to donating sperm, the American Association of Tissue Banks sets the maximum age for donors at 39. "The age of the male does become more of a factor in their late 40s," said Werlin. "Up until that point, it’s not so much."

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Which begs the question: Why? If sperm is three months old regardless of a man's age, what, if anything, changes?

Older paternal age and birth defects

As Smith lays out in¬†his paper, a growing body of¬†research suggests that advanced paternal age is associated with a range¬†of birth defects‚ÄĒfrom autism to obesity to schizophrenia.

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But some experts question if correlation can really be linked to causation. How do researchers know (or think they know) that older sperm is leading to issues?

"Data suggests that men over 40 have children with more birth defects," said California Cryobank's Brown. "However, the question is raised: Are their partners older? Are there medical techniques being used which affect those outcomes? What's the connection?"

Experts believe that¬†egg health matters most when it comes to fertility, so is it possible that men over 40 have female partners over 40, and that's accounting for the higher rate of birth defects? The short answer is¬†yes‚ÄĒit's possible.¬†As Smith told Fusion, the issue can be "difficult to disentangle."

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And yet, certain specific mutations are associated with paternal, not maternal aging. For example, studies have shown that advanced paternal age is associated with a higher likelihood of bipolar disorder and obesity, but advanced maternal age is not.

So what's happening to sperm in men over 40?

Turns out, the quality of an older man's sperm might have less to do with the age of the sperm itself and more to do with the age of the materials it comes from.

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"Although the sperm cells are indeed ‚Äėyoung‚Äô, the stem cells (from which sperm cells are derived) remain in the testis throughout the life of the male, and it is these stem cells that suffer an accumulation of mutations," Smith told¬†Fusion in an¬†email.

"When stem cells divide to produce cells that will give rise to sperm, mutations harboured by the stem cells will end up in the sperm."

Which could explain the correlation in birth defects seen in the children of men over 40, even when controlling for maternal age‚ÄĒand also explains why Smith is urging young men to consider freezing their sperm sooner rather than later.

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Of course, choosing to freeze one's sperm and keep it frozen indefinitely is easier said than done. In the U.S., it costs roughly $400 per year to preserve one's sperm, which can add up over the years.

Werlin, the reproductive endocrinologist in Irvine, told Fusion that the only men he sees freezing their sperm are cancer patients facing chemotherapy, military men leaving on deployments, and first responders (firefighters and police officers) who want to protect their sperm if anything goes wrong on the job.

Brown at Cryobank said the same, but did add, "We¬†are seeing a slight movement toward fertility preservation. We see some healthy guys freezing who are 25. We‚Äôve had a handful of those"‚ÄĒwith a strong emphasis on handful.¬†(Notably, he says he doesn't see many women in their 20s freezing their eggs, either.)

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When asked if more young, healthy men should start freezing as a protective measure, Brown was hesitant: "I don't know a physician who would recommend it at 18."

And Werlin noted that there can be such a thing as too much pressure on fertility. When healthy young couples start out viewing pregnancy as a medical challenge, "I think that it puts one more stress factor into a difficult situation right from the get go … the hard part is once you start fertility treatments and testing, things change dramatically," he said. "What was once a pleasurable experience becomes a mechanical one."

Smith, of course, disagrees, believing that the problem of flawed sperm will only grow as time goes on and more men put off fatherhood:

"If it is true, as some scientists in the field have suggested, that the background de novo mutation rate will lead to a substantial reduction in human fitness over the next few centuries, and if the demographic trend of advancing paternal age continues and thus accelerates this decline, it follows that some attention should be given to the future in terms of considering what might be done to combat this potential genetic decline."

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Smith told¬†Fusion, "State sponsorship [for sperm freezing]‚ÄĒwith all the benefits that economies of scale would bring‚ÄĒwould indeed be my suggested best option."

Who knows, perhaps the concept of the friendly neighborhood "bank" will take on a whole new meaning for our children's children.

Taryn Hillin is Fusion's love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn ‚ÄĒ not necessarily in that order.