When most people think about semen quality, they think about fertility. But science is telling a bigger, more surprising story: your swimmers might also say something about your long-term health — even how long you live.
Yep, really.
A massive 50-year study from Denmark suggests that semen quality isn’t just about making babies. It may be one of the most overlooked biomarkers of men’s overall wellbeing. At SHA, we’re all about science that’s human and accessible, so let’s dive into what researchers found — and explore the emerging frontier of the semen microbiome.
Semen 101
New semen is produced regularly in the testicles.
Common findings in semen analysis
Low sperm count (oligospermia): <15 million sperm per milliliter or <39 million total.
No sperm (azoospermia): occurs in ~10% of infertile people and ~1% of all individuals producing semen. This doesn’t always mean the testes aren’t producing sperm — sometimes there’s simply not enough in the ejaculate to measure.
Why counts may be low
Medical conditions: varicocele (swelling of testicular veins), infections, hormonal imbalances, or medications.
Environmental/lifestyle factors: industrial chemicals, heavy metals, radiation, heat exposure, smoking, alcohol or drug use, stress, poor diet, lack of exercise, and insufficient sleep.
Low counts often prompt further testing, and interventions and treatments are available. Global sperm counts have been declining, likely due to these combined factors.
A Quick Study Recap: 78,000+ Men, 50 Years of Data
Researchers in Copenhagen followed 78,284 men who had semen tests between 1965 and 2015, capturing the full spectrum of semen quality — from azoospermia to extremely high counts.
They tracked:
Semen volume
Sperm concentration
Motility (how well the sperm move)
Morphology (their shape)
Total sperm count
Total motile sperm count (the superstar predictor)
Using Danish national registries, they followed these men for a median of 23 years — making this one of the largest and longest semen-and-health studies ever conducted.
Better Semen Quality = Longer Life
Men with >120 million motile sperm lived ~2.7 years longer than men with just 0–5 million motile sperm.
High motility group: ~80.3 years
Low motility group: ~77.6 years
The relationship was dose-dependent: more motile sperm means a lower mortality risk. Less motile sperm means higher risk. This held even after accounting for education and preexisting diseases, suggesting semen quality is an independent marker of overall health.
Why Would Semen Quality Predict Lifespan?
This is the fascinating part.
Hormonal balance
Good blood flow
Low inflammation
Healthy metabolic function
A well-functioning immune system
In other words, the same systems that support sperm are the systems that support whole-body health.
If something in the body isn’t functioning well, sperm can often show it.
Think of semen quality as a check engine light for biological wellbeing.
The New Frontier: The Semen Microbiome
Yes, semen has a microbiome!
Just like your gut, mouth, vagina, and skin, semen has its own microbial ecosystem — the semen microbiome.
Previously thought sterile, semen actually contains its own microbial ecosystem, influenced by age, sexual debut, lifestyle habits, circumcision status, and geography.
Common players in the semen microbiome:
A diverse community of microorganisms such as:
Lactobacillus (usually the “good guys”)
Gardnerella
Prevotella
Ureaplasma
Other anaerobic bacteria
A Lactobacillus-rich semen microbiome often correlates with higher sperm quality, though the science is still emerging and this trend hasn’t held up across all studies. Each person’s microbiome is unique, like a microbial fingerprint. And, we are far from fully understanding the implications of this dynamic world.
Why this matters for sexual health:
Research is showing that the semen microbiome can influence:
Sperm motility
Sperm shape
DNA fragmentation
Seminal inflammation
Fertility outcomes
Genital tract comfort and irritation
Imbalances (dysbiosis) are linked to lower sperm motility, poor morphology, oxidative stress, and inflammatory responses. Lifestyle, environment, and stress can all influence this microbial world — potentially connecting semen health to overall health and aging.
What This Means for Men’s Health (Beyond Fertility)
This study suggests that semen quality is more than a reproductive metric. It might be:
a window into long-term health
a clue about biological aging
a useful marker for chronic disease risk
And as we learn more about the semen microbiome, we may discover new ways to:
support fertility
improve sexual wellness
reduce inflammation
potentially support healthier aging
Think of semen as a little snapshot of overall wellness — one worth paying attention to.
Practical Takeaways for SHA Readers
Because we love a real-life angle:
Semen quality may reflect whole-body health.
Tracking semen health isn't only for people trying to conceive — it’s also a wellbeing check.
The semen microbiome is real, and it matters.
Lifestyle choices that improve heart, metabolic, and hormonal health also tend to improve semen.
Sex-positive takeaway: Male pleasure and wellness are deeply connected — literally from the inside out.
A More Holistic View of Male Sexual Health
This Danish study adds to a growing body of evidence that semen quality offers clues about the body’s broader health story. When paired with emerging microbiome research, we’re starting to see semen as more than a reproductive fluid — it's a reflection of the interconnectedness of sexual and systemic health.
And that’s exactly the kind of whole-person, sex-positive science SHA is here to explore.
Interested in learning more?
SHA’s Male Sexual Health and Functioning Conference this December, where global experts will discuss topics including erectile dysfunction, testosterone and hormones, and inclusive care for queer, trans, and nonbinary clients assigned male at birth. You’ll gain practical insights into helping clients navigate both physical and emotional challenges while building confidence, connection, and healthier sexual lives.
Resources:
Written by Emma Sell-Goodhand, MPH
Emma is a doctoral student and Global One Health Fellow at North Carolina State University studying adolescent sexual health. She brings prior experience as a Technical Advisor at the World Health Organization.
Want to become an in-demand sexual health professional? Learn more about becoming certified with SHA!
