When it comes to health, we often assume that more is always better. If five servings of vegetables a day are good, then surely seven or eight must be even better, right?
The same logic often gets applied to exercise. The CDC and British Heart Foundation recommend 150 minutes of moderate activity or 75 minutes of vigorous cardio per week—and many runners proudly exceed that baseline.
But where’s the line between healthy and harmful?
Can running too much backfire? Logging a 5K, 10K, or even a half-marathon clearly supports fitness and longevity—but what about going all the way to 26.2 miles? Could running a marathon actually be detrimental to your health?
Is Running a Marathon Bad for You?
Perhaps there is no question more polarizing between the running community and non-runners than, “Is running a marathon bad for you?”
After all, runners will defend the innumerable benefits of running tooth and nail against anyone who raises questions about the essential risks.
It’s most important to establish right off the bat that we believe that, by and large, running is absolutely one of the best things that most people can do for their body, mind, and overall health, unless you have certain pre-existing conditions that otherwise make running unsafe.
With that said, trying to approach the research about the safety of marathon running with an unbiased opinion and open mind brings us to consider the potential risks that can be involved with putting your body through running a full 26.2 miles.
Ultimately, what differentiates running a marathon from running in general or focusing on shorter distances, whether recreationally or competitively, is indeed the marathon’s long distance itself.
When you are discussing the benefits of running in a broad sense, the term “running“ can encompass just about anything.
From a very low-intensity walk/jog method to jogging 30 minutes a day most days of the week to satisfy the physical activity guidelines, to training for and competing in high-level 5k races, to running on the trails with your dog, to training for one marathon after the next, it’s all considered running.
Along the very broad continuum of how people might participate in the sport of running, certain engagement levels may or may not be more appropriate or healthy for the body than others, depending on your overall health, fitness level, and the amount of running itself you are doing.
For example, running a marathon might be perfectly healthy and reasonable for someone who is of good health and takes plenty of time to train, gradually increasing distance, listening to their body, feeling well, recovering adequately, and making any adjustments to training when they need to back off for one reason or another.
On the other hand, running a marathon might be a bad idea for someone who has virtually no experience and wants to do a “crash course“ in preparing for the marathon, running way harder than their body is ready to endure, ignoring all pain or signals that they need to back off, and placing the importance on training above all else in regards to their health.
Additionally, someone with a known heart condition and who has been advised against taxing their heart during longer workouts would also not be a good candidate to safely run a marathon unless otherwise cleared by their cardiologist.
As we explore the potential risks of running a marathon and ways that running a marathon can take a toll on your body, it’s important to bear in mind that this doesn’t necessarily mean that running itself is bad or that running a marathon is inherently bad for everyone.
Potential Negative Effects of Running a Marathon
#1: Cardiac Events
The most concerning and frequently cited reason that running a marathon could be bad for your body is the potential risk of sudden cardiac arrest or other serious heart events.
There have certainly been tragic instances of seemingly healthy marathoners—both young and old—experiencing cardiac arrest during races. In some cases, medical personnel were unable to intervene in time, or the cardiac abnormalities were too severe to reverse.
Earlier research has shown that sudden cardiac death in young athletes (ages 12–35) is about 2.5 times higher than in non-athletes of the same age, and other studies have suggested that marathon running may increase the risk of myocardial fibrosis.1Wilson, M., O’Hanlon, R., Prasad, S., Deighan, A., MacMillan, P., Oxborough, D., Godfrey, R., Smith, G., Maceira, A., Sharma, S., George, K., & Whyte, G. (2011). Diverse patterns of myocardial fibrosis in lifelong, veteran endurance athletes. Journal of Applied Physiology, 110(6), 1622–1626. https://doi.org/10.1152/japplphysiol.01280.2010
Biochemical and functional heart abnormalities are also fairly common after a marathon, though in most cases these are transient and resolve without lasting damage.
Much of the concern around marathons stems from the link to coronary artery disease (CAD). Research has shown that about 73% of sudden cardiac deaths among older marathoners and joggers are attributable to underlying CAD. 2Virmani, R., Burke, A. P., Farb, A., & Kark, J. A. (1997). CAUSES OF SUDDEN DEATH IN YOUNG AND MIDDLE-AGED COMPETITIVE ATHLETES. Cardiology Clinics, 15(3), 439–466. https://doi.org/10.1016/s0733-8651(05)70351-9
Proper medical screening and on-course emergency preparedness—such as having trained personnel and automatic external defibrillators (AEDs)—play a significant role in reducing these risks.
New insights from the Race Associated Cardiac Event Registry (RACER):
A massive updated analysis looking at US marathons and half-marathons between 2010 and 2023 provides some encouraging news.3Kim, J. H., Rim, A. J., Miller, J. T., Jackson, M., Patel, N., Rajesh, S., Ko, Y.-A., DiGregorio, H., Chiampas, G., McGillivray, D., Holder, J., & Baggish, A. L. (2025). Cardiac Arrest During Long-Distance Running Races. JAMA. https://doi.org/10.1001/jama.2025.3026
Among more than 29 million finishers, there were 176 documented cardiac arrests—a rate of just 1 in every 166,667 runners. Importantly, survival rates have more than doubled since earlier reports. From 2000–2009, only 29% of runners survived cardiac arrest during races; from 2010–2023, survival jumped to 66%.
This improvement is primarily credited to the widespread availability of bystander CPR and defibrillators along racecourses.
The study also confirmed that men face a higher risk than women (1.12 vs. 0.19 per 100,000), and marathoners more than half-marathoners (1.04 vs. 0.47 per 100,000). CAD was the leading cause of cardiac arrest, accounting for 40% of cases, while hypertrophic cardiomyopathy was far less common than once believed (7%).
The key takeaway: while the risk of cardiac arrest during marathons is real, it remains extremely rare, and thanks to improved medical response, survival outcomes are better than ever.4Day, S. M., & Thompson, P. D. (2010). Cardiac Risks Associated With Marathon Running. Sports Health: A Multidisciplinary Approach, 2(4), 301–306. https://doi.org/10.1177/1941738110373066
Ultimately, the benefits of endurance running still outweigh these risks for most healthy runners. Most serious cardiac events occur in individuals with pre-existing heart disease, meaning prevention through screening and awareness is possible.
When placed in context, the “robust association of endurance running with improved quality of life and longevity” underscores that marathons remain a net positive for the majority of runners.
#2: Increased Risk of Injuries
Running is a high-impact, repetitive activity, so runners are prone to various musculoskeletal injuries. This risk is heightened with training for a marathon due to the necessary mileage and pounding on the body.
A large review looked at all of the potential health implications of distance running, with races ranging from the 10k to ultramarathons.5Wirnitzer, K., Boldt, P., Wirnitzer, G., Leitzmann, C., Tanous, D., Motevalli, M., Rosemann, T., & Knechtle, B. (2022). Health status of recreational runners over 10-km up to ultra-marathon distance based on data of the NURMI Study Step 2. Scientific Reports, 12(1). https://doi.org/10.1038/s41598-022-13844-4
Unsurprisingly, marathon running was associated with an increased risk of running-induced injuries, such as knee pain and stress fractures, with approximately half of the active runners reporting having more than one injury per year.
Risk factors identified with a greater chance of experiencing a running injury were excess body weight, higher weekly mileage, and marathon or ultramarathon running as opposed to 10k or half-marathon running.
In other words, there’s a greater risk of getting injured training for a marathon than when running shorter distances.
At the same time, consistent running can also protect against certain injuries by strengthening bones, muscles, and connective tissue, while improving balance, coordination, and overall durability.
You can reduce your risk during marathon prep by progressing mileage gradually, prioritizing recovery, and paying attention to mobility and flexibility work to keep joints moving well.
Building a strong foundation through resistance training helps support the repetitive stress of running, while proper footwear and wise surface choices further minimize unnecessary strain.
Taken together, these strategies not only lower the risk of overuse injuries but also make you a more resilient, well-rounded athlete.
#3: Kidney Damage
There is some evidence to suggest that marathon running can temporarily stress the kidneys, even when hydration is adequate.
Studies have shown that more than half of marathon finishers display signs of acute kidney injury (AKI) immediately after racing, with elevated biomarkers indicating reduced filtration and tubular stress. The good news is that, in nearly all cases, kidney function returns to baseline within 24–48 hours as the body recovers.6Hernando, C., Hernando, C., Panizo, N., Collado-Boira, E., Folch-Ayora, A., Martínez-Navarro, I., & Hernando, B. (2022). Renal Function Recovery Strategies Following Marathon in Amateur Runners. Frontiers in Physiology, 13. https://doi.org/10.3389/fphys.2022.812237
Researchers are still exploring whether repeated episodes of this acute stress could contribute to long-term kidney problems in habitual marathoners.7Pasternak, A. V., Newkirk-Thompson, C., Howard, J. H., Onate, J. C., & Hew-Butler, T. (2023). Four Cases of Acute Kidney Injury Requiring Dialysis in Ultramarathoners. Wilderness and Environmental Medicine, 34(2), 218–221. https://doi.org/10.1016/j.wem.2022.12.004
At present, the evidence is limited and largely speculative. Severe or prolonged kidney damage tends to occur only in rare cases, often when other risk factors are present—such as dehydration, extreme heat, prior kidney issues, or the use of NSAIDs during the race.
In other words, while marathon running clearly places temporary strain on the kidneys, for most healthy runners this appears to be a short-lived response rather than a chronic problem.
Still, it underscores the importance of respecting recovery and staying well hydrated.
#4: DNA and Muscle Damage
Some studies have found that marathon running can cause both muscle damage and oxidative DNA damage, with the degree of harm increasing as the race distance gets longer.8Ryu, J. H., Paik, I. Y., Woo, J. H., Shin, K. O., Cho, S. Y., & Roh, H. T. (2016). Impact of different running distances on muscle and lymphocyte DNA damage in amateur marathon runners. Journal of Physical Therapy Science, 28(2), 450–455. https://doi.org/10.1589/jpts.28.450
Amateur runners who completed 42 km showed significantly higher levels of muscle damage markers (creatine kinase and lactate dehydrogenase) and greater lymphocyte DNA damage compared to those running 10 km or 21 km.
However, these effects were temporary, as most markers returned to baseline within three days of recovery.
In short, while endurance running—especially the full marathon—places notable stress on the body at the cellular level, trained runners appear capable of repairing this damage relatively quickly, highlighting both the physiological cost and resilience involved in long-distance racing.
Our goal isn’t to scare you off from marathon dreams—it’s to ensure you’re informed.
Like any demanding sport, running carries some risks, and it’s smart to talk through your personal health status with a healthcare provider.
But for healthy adults, the evidence is clear: the benefits of running overwhelmingly outweigh the risks. Ready for the uplifting part? Flip the coin and dive into the many upsides—physical and mental.
Check out our guide, 26 Powerful Benefits of Running, to see why lacing up is so worth it.
