Sperm DNA Fragmentation: What Is It and Is It Worth Testing?

It's men's health week this week - so I thought it was a good time to talk about Sperm - specifically about Sperm DNA fragmentation.

Sperm DNA fragmentation testing is having a bit of time in the sun at the moment. It's becoming an increasingly popular test among couples with unexplained infertility.

But what's actually being tested – and why? This article breaks it all down in simple terms, drawing on my more than 20 years of experience as an embryologist and fertility educator. Keep reading to the end where I also share my recommendations on what you can do to protect and improve sperm quality, whether or not you get a sperm DNA test.

What is Sperm DNA Fragmentation and What Causes It?

Sperm DNA fragmentation refers to damage or breaks in the DNA strands of the sperm, which makes it harder for the sperm to fertilise an egg successfully. It's one of the major causes of male infertility.

The causes of these DNA breaks generally fall into two buckets – things that happen inside the sperm itself, and things that come from the outside environment.

• Intrinsic factors: Natural issues within the sperm itself, such as problems during sperm production, ageing, or genetic defects, can compromise sperm DNA integrity and make it more likely to break.

• Extrinsic factors: Outside influences like smoking, vaping, alcohol, high stress, infections, chemotherapy, environmental toxins, or even exposure to heat (think hot tubs and saunas) can cause sperm DNA damage over time.

I know of many scientists and researchers in my field who hope that further sperm DNA fragmentation analysis and study may help to improve fertility outcomes, including raising the success rates for IVF, ICSI, and other assisted reproductive technology treatments.

Interestingly, the oocyte (egg) can sometimes repair sperm fragmentation, depending on the type and severity of the damage and the quality of the egg. Since both egg and sperm quality decline with age, this phenomenon is more likely to occur with younger couples.

How Does Sperm DNA Fragmentation Actually Happen?

At the cellular level, sperm DNA damage is often driven by reactive oxygen species (ROS). These are unstable oxygen molecules that the body naturally produces, but when levels get too high – a state known as oxidative stress – they can attack and break the DNA strands inside sperm. This process is sometimes referred to as deoxyribonucleic acid fragmentation.

When too many DNA breaks occur, the overall sperm chromatin integrity (the way DNA is packaged and protected within the sperm head) is weakened. Chromatin that is loosely packed or poorly protected is more vulnerable to further damage.

It’s also important to distinguish between fragmentation and other genetic issues like sperm aneuploidy, where sperm carry the wrong number of chromosomes. Both conditions can negatively influence fertility, but fragmentation specifically refers to physical breaks in the DNA, while aneuploidy is about chromosome number errors.

In most cases, the sperm that are healthiest and most tightly packaged – in other words, the fully mature sperm – are less likely to show fragmentation compared with immature ones. This is why fertility experts often focus on encouraging or selecting mature sperm wherever possible.

What Are the Symptoms of Sperm DNA Fragmentation?

Unfortunately, there are no obvious symptoms of sperm DNA fragmentation. The ejaculated sperm will be entirely 'normal' and is also often accompanied by a completely 'normal' semen analysis.

While sperm with fragmented DNA can sometimes still fertilise an egg, the consequences often appear later, affecting embryo quality and overall pregnancy outcomes. For example, increased DNA fragmentation has been linked with:

• Longer time to pregnancy

• Implantation failure

• Impaired embryo development

• Recurrent miscarriage

However, none of the above are solid evidence that DNA damaged sperm is the underlying problem. There are many factors that can affect both female and male fertility, meaning the issue (or issues) in your case could be completely unrelated.

Are There Tests for Sperm DNA Fragmentation?

Yes, there are several laboratory tests designed to assess sperm cells for DNA fragmentation. Each works a little differently and provides slightly different information:

• Sperm Chromatin Structure Assay (SCSA): Uses flow cytometry to measure how vulnerable sperm DNA is to breaking. It’s one of the most widely used tests.

• TUNEL Assay: Detects actual breaks in the DNA strands by attaching a fluorescent marker, allowing damaged DNA to be visualised under a microscope.

• COMET Assay: Involves running sperm DNA through an electric field; broken strands trail behind like a comet tail, making the amount of fragmentation measurable.

• Sperm Chromatin Dispersion Test (SCD): Looks at the way sperm DNA disperses after the nuclear proteins are removed; poor dispersion suggests higher fragmentation.

Are Sperm DNA Tests Worth It?

At first glance it might seem simple – why not just do a test and find out if high sperm DNA fragmentation is the problem?

The challenge is that, as explained above, there are several different types of tests available. Each one will measure sperm DNA damage in a slightly different way, which means results can vary and sometimes add more confusion than clarity.

Other limitations: these tests aren’t sensitive enough to give the full picture of sperm health, and there’s still no agreed cut-off value for what counts as a ‘normal’ level of sperm DNA strand breaks.

In other words, a result that comes back as 'no problem' doesn’t always mean the DNA in the sperm sample was completely healthy – it just means the test didn’t detect an issue.

I love this sperm DNA fragmentation SWOT analysis published by Agarwal et al in 2020:

It shows us that sperm DNA fragmentation testing can give us useful information in some situations, but the quality of the evidence is not great and filled with lots of contradictions.

So for this reason, sperm DNA testing is not universally recommended – and added to that, it's pretty expensive!

So What Should We Do Instead of Testing?

Since most test results lead to the same advice – make lifestyle changes – it often makes sense to skip the expensive tests and just start there. Even without a test result, these changes are generally simple, practical, and beneficial for both sperm health and overall health.

Lifestyle changes that help protect sperm DNA include:

• An antioxidant-rich diet: Foods high in vitamins C and E, zinc, selenium, and other antioxidants help reduce oxidative stress and protect sperm chromatin integrity. Aim for a diet rich in colourful fruits, vegetables, nuts, and wholegrains.

• Exercise and stress management: Keeping active helps regulate hormone balance and reduce your stress levels (high stress can interfere with sperm quality).

• Better sleep and metabolic health: Getting good quality sleep (and enough of it!) supports hormone regulation. Likewise, keeping a healthy weight is linked to healthier sperm.

How Do Toxins Affect Fertility?

When I work with clients, the exact recommendations depend on their situation. But almost always, the first step is reducing exposure to environmental toxins. The obvious culprits are alcohol, smoking, and vaping – but there are also less obvious ones, like heavily scented aftershaves, body sprays, and even some laundry detergents.

To understand why this matters, it helps to think of sperm production in three stages:

• The sperm factory (seminiferous tubules in the testicles): where sperm are first created, supported by specialised helper cells called Sertoli cells.

• The warehouse (epididymis): where sperm are stored and matured, needing a stable environment that isn’t too hot or exposed to radiation.

• The delivery system (vas deferens, plus the seminal and prostate glands): where sperm mix with other fluids to form semen – and where toxins can easily be introduced.

Interestingly, only about 5% of semen is actual sperm; the rest comes from those glands in the delivery system. That’s why optimising each stage is important if we want sperm to be as healthy as possible.

Environmental toxins play a bigger role in fertility than most people realise. They can disrupt hormones, interfere with sperm development, and ultimately reduce the chances of successful reproductive outcomes – both naturally and through in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI).

Get some help understanding hormones and environmental toxins by heading to my Detox WTF course here (the first session is free to watch!)

Oh, and if you want to understand more about a semen analysis - head to THIS BLOG

REFERENCES

1. Hamilton TR dos S, Assumpção MEOD. Sperm DNA fragmentation: causes and identification. Zygote. 2020;28(1):1-8. doi:10.1017/S0967199419000595
   

2. Agarwal A, Majzoub A, Baskaran S, Panner Selvam MK, Cho CL, Henkel R, Finelli R, Leisegang K, Sengupta P, Barbarosie C, Parekh N, Alves MG, Ko E, Arafa M, Tadros N, Ramasamy R, Kavoussi P, Ambar R, Kuchakulla M, Robert KA, Iovine C, Durairajanayagam D, Jindal S, Shah R. Sperm DNA Fragmentation: A New Guideline for Clinicians. World J Mens Health. 2020 Oct;38(4):412-471. doi: 10.5534/wjmh.200128. Epub 2020 Aug 6. PMID: 32777871; PMCID: PMC7502318.