So swimmers age faster ?

Disclaimer: no medals, no lap times, no chlorine. This is about a very different kind of swimmer — one with a much higher stake in the race.

I caught, from a quick informational video, a claim from a new scientific study: that the biological clock isn’t as critical for us as women — it’s actually faster in men, in their swimmers, mainly because mutation rates are higher and are potentially the cause of malformations in embryos. That was shocking, and I really believed it, both because of the way the presenter explained it and because she showed the scientific report at the end of the video.

Also, a personal story made me wonder more and more about the fallacies, the verisimilitude, and the mistakes surrounding this topic.

A kind reminder: in scientific research we deals in probabilities, enough to suggest theories, but never enough to be 100% sure we’re talking about a general phenomenon. Scientists are obligated to suggest conclusions, but be critical too when a doctor of medicine suggests something to you, because some people talk as if they held the only truth. Being critical is what saved me from almost believing I might have fertility issues.

It’s widely known, shared, and rumored that women’s eggs age faster than men’s swimmers. So I got motivated to dive deeper into the topic — first, because I was close to the age where the numbers and probabilities say I have my last chance to preserve my oocytes through freezing (cryopreservation), which has become a “solution” to today’s privileged reality for women, where some of us can still choose to develop our careers and independence instead of having children and becoming moms in our early 30s. (Controversial sentence — the word “privilege” will never fit neatly here. I’ll get into the why behind that in another essay.)

Diving into the ins and outs of the specifications behind freezing and preserving oocytes, I realized the process is more invasive than it sounds, and even so, it still doesn’t guarantee 100% success in getting pregnant. First, you need to be sure you have enough follicles (future oocytes) to freeze — some women don’t pass this stage. Then, once you’ve produced enough, after artificially inducing them to maturation (via hormonal injections that make your follicles grow into mature eggs faster — sometimes several rounds are needed), the mature oocytes are frozen and made available for in vitro fertilization. From there, the percentage of fertilized oocytes retrieved drops again — not necessarily because of us, but because of the swimmers, which I’ll get into further below. Looking at the report numbers, if I freeze my oocytes at 29, I’d have a 40–50%, maybe up to 58%, chance of successful fertilization if I use them before turning 35, and that percentage would drop the longer I wait, falling to around 26% if I use them at 40. After seeing this, I made the personal decision not to put my body through all that disruption — to force it, via external hormones, to generate more eggs and then freeze them with less than 50% certainty that it would work later. I’m not saying it isn’t a good plan. As I said, it was a personal decision, made after confirming my body was healthy enough to generate a good number of eggs for a while longer, and after verifying the information that follows.

So do swimmers age faster?

Swimmers from a younger male (25–35) have the highest rate of healthy fertilization, and their chances start to decline after 35, more sharply after 40 — close to the age of women’s “biological clock,” right? But what exactly declines? Semen volume, motility, and also the rate of sperm malformation increases, which is linked to disrupting or preventing fertilization. So, in a few words: no, swimmers don’t age faster than women’s eggs. Both age at a fairly similar rhythm, but there are some differences worth taking into account. Based on the original source — the woman in the video making that claim — I went to the scientific report to understand what the findings actually were.

This Sci-Adv-publication study looked at the “resilience” of the oocyte in the face of allele mutations. In other words, it suggests that oocytes, regardless of the age at which they were produced, are less susceptible to carrying mutations — and therefore less likely to pass on human malformations to a fertilized future baby. This debunks the rumor and belief that a woman who carries a baby later in her “fertility age” is more likely to give birth to a baby with diseases or health problems. So that’s one of the claims of the research: oocytes are protected and remain fertile and healthy regardless of the woman’s age at the time they were produced. A real difference from sperm is that oocyte aging is gradual, while sperm quality declines quite fast after 40 — and, per the same finding, sperm can potentially pass on allele mutations to newborns.

What About the Left-Out Parts?

I kept wondering about the left-out parts of this research — most of it evaluated on Caucasian populations, mainly from European or US databases, as pretty much always happens in human research. I just wondered if there was some other, more inclusive and realistic research cohort on women’s fertility, for example: do Hispanic, African, Asian, and European women share the same age rates of fertilization? Guess what? … Yes, we do. We’re pretty much equal, and that’s another part of the oocyte’s biological nature that we share as humans. Unfortunately, data on men from different parts of the world doesn’t hold the same way. Spoiler: swimmers are more susceptible to environment too. Bad news: a database on Chinese men, for example, suggests sperm become less fertil in higher-temperature zones; good news: other cohorts from India and Turkey suggest sperm fertility doesn’t decline until closer to 50.

Nevertheless, it’s important to consider that fitness could help some individuals become outliers, as I said from the beginning, in science we’re always talking about probabilities.

One thing really holds true for both swimmers and eggs: having a healthy lifestyle and regularly monitoring your own data, with a professional who explains the whys behind things, can make you more aware of your situation and help you make better decisions accordingly.

Thanks for reading.