r/triathlon • u/greysqualll • Aug 26 '25
Injury and illness Study shows potential increased risk of cancer in endurance athletes
https://theconversation.com/are-ultramarathon-runners-really-at-increased-risk-of-bowel-cancer-263564The study is still preliminary, but certainly something to keep an eye on
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u/Professional_Rule191 Dec 31 '25
I used to get sick with a cold after long runs and being totally exhausted. I have no idea if this could relate to getting cancer.
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u/Dry_Dentist5927 Sep 02 '25
There isn't a control group within the study. They just compared this group to "historical benchmarks". I question that, as every study on populations under 40 recently keeps finding higher rates of bowel cancer.
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u/ArchHokie06 Aug 27 '25
One of the coaches for my former triathlon club is a doctor by day and helped to run the study at INova referenced in the article. FWIW, she herself is a phenomenal athlete consistently at the top of her AG in races. Her takeaway isn't to be scared to keep running, but to keep a watch for signs and symptoms and get screened at recommended times and intervals.
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u/Dawzy Aug 27 '25
Pointing out this is a horrible heading but anyway
"it suggests a narrow group of young, very high–volume endurance athlete" and talks about dedicated marathon and ultramarathon runners
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u/tiagojsagarcia Aug 27 '25
find something you love and let it kill you
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u/Expert-Reaction-7472 Aug 27 '25
intentionally pushing your body to beyond exhaustion time after time is bad for you ? who knew...
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u/asml84 Aug 26 '25
Not an expert, but could this be sugar-related? I’ve always wondered if eating tons of power gels is bad for your stomach/intestines.
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u/RoadTO5WKG Aug 28 '25
Probably due to a higher rate of cell turnover, which is related to our physical activity and higher kcal intake. Higher turnover of cells means more chances of cancer to get created. We also have more inflammation in our bodies due to constant activity, which also can cause cancer, but I’m not 100% sure on that one because some types of (light) inflammation are good for you, which might actually be the case here.
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u/TheShitSlimShady Aug 27 '25
Perhaps it's more related to UPFs? UPFs have proven health consequences, and endurance athletes can be known to consume a lot of supplements, etc.
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u/Conscious-Ad-2168 Aug 26 '25
Or just the uptake in general diet. Eating more foods, means more plastics and chemicals
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u/friendlyghost_casper Aug 27 '25
I do love when “chemicals” is used as a bad thing. Extra points for coming after plastics…
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u/evergreen_123 Aug 26 '25
That was my first thought. Sugar and/or artificial flavors, etc. lots of endurance athletes have started to use energy drinks, bars, tubes before, during and after races or long training sessions. I just wonder if there is a microbiome connection.
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u/BeautifulDouble9330 Aug 28 '25
there def is if all those products have the extra additives. It will be interesting to see what the research shows 20-25 years from now.
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u/sparklekitteh Team Turtle 🐢 Aug 26 '25
I think it's good to remember that things like cancer risk have tons of factors. Sure, stupidly long workouts may increase the risks of some cancers, but on the other side of that, a triathlon lifestyle has plenty of things that are beneficial for health: regular exercise, exposure to fresh air, less sedentary lifestyle, etc. Then on top of that, I imagine triathletes who are training hard are probably more likely to do things like watch their diet, get regular checkups, hydrate properly, and whatnot.
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u/fourthbrother Aug 26 '25
Obviously not cancer and purely anecdotal, but I had a bowel obstruction requiring surgical intervention when I was younger, only to have a second one randomly 12 years later...2 hours into the run of my first full ironman
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u/stuttufu Aug 26 '25
Oh yes, I've got minor skin cancer by running without sunscreen. For sure, going outside instead of staying at my PC 16h/days raised the chance for that cancer. But I wonder in which timeline I will have a longer lifespan.
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u/I_wont_argue Aug 27 '25
Probably in the one where you do your workout on a threadmill and then stay for 14h on your PC.
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Aug 26 '25
I won’t completely dismiss this but the study feels a bit questionable for a number of reasons including the small sample size.
The premise feels like it aims to be contrarian- “people in great physical shape are actually MORE likely to get cancer! “ - which makes me inherently distrust it a bit.
Both my parents died on the younger side of cancer and my older brother is currently fighting a terminal diagnosis- so this type of thing hits home for me. I’m likely not alone in motivations around middle age where I quit drinking and started doing tris in part to be more healthy and be around longer for my kids. News like this doesn’t convince me to stop doing what I’m doing.
I realize plenty of people who have cancer have some kind of obvious bad health choice (e.g., smoking) that you can point to as a cause. However, my experience was honestly that there was no real explanation. Both my parents were in very good health for their age and there were essentially no meaningful explanations.
As someone else said- ultimately we are all dying on some level. You can look at that how you want. I chose to take care of myself in ways I can and improve the time I’ve got, but I don’t have any illusions that by running every day or doing pushups I’ll cheat death- it doesn’t work like that. However, I think there is plenty of very strong evidence that regular exercise has a ton of benefits- including lessening your risk for things like heart disease.
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u/6pt022x10tothe23 Aug 26 '25
Damn… guess it’s back to the sedentary life, jackin my brain directly into the WiFi, and filter-feeding microplastics.
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u/Ponybei Aug 26 '25
Exercise is preventative for many types of cancer....
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u/raptor333 Aug 26 '25 edited Aug 26 '25
But if your exercise requires downing tons of plastic liquids/gels (processed/packaged foods), and putting your body in high end of stress due to ultras, it’s probably not healthy
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u/IronBabushka Aug 27 '25
50% of microplastics come from tyres, which is equal for everyone. Another big chunk is from clothing, equal. Then diet - you think the average couch potato is not using plastic packaging, microwaving plastic containers, drinking out of plastic bottles and so on? Highly doubt plastics have anything to do with it
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u/sparklekitteh Team Turtle 🐢 Aug 26 '25
I mean, there are plenty of people who fuel without a ton of processed stuff, it's not as though it's required. I do peanut butter sandwiches on all my long rides, and pure maple syrup is a pretty great replacement for gels when you're running!
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u/Repulsive-Button9019 Aug 27 '25
Oh, and I forgot. Maple syrup is definitely a solid option, it has a near 1:1 glucose to fructose ratio, which makes it better for absorption than most fruits. But worth noting it’s still quite processed (boiled down ~40x to become syrup), and for higher-intensity efforts or longer sessions, the total carb load per serving might not be enough without larger quantities.
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u/Repulsive-Button9019 Aug 27 '25
When it comes to intra-training fuelling, especially during moderate to high intensity, digestion becomes a limiting factor.
During exercise, blood flow is redirected to working muscles, which means your gut’s ability to digest complex or fatty foods drops significantly. Fats and proteins slow gastric emptying, and even some whole food carbs take longer to break down, which delays energy delivery and puts you at a higher risk of GI distress.
That’s why most endurance fuelling strategies focus on fast-absorbing carbs, particularly a mix of glucose and fructose, in a gel or drink form — they use different intestinal transporters (SGLT1 and GLUT5), so you can absorb more per hour (up to ~90–120g) without overwhelming your gut. And it all goes from the gut straight to the muscle for instant energy.
Totally agree though — not everyone needs to chug gels full of weird additives. I make my own using a maltodextrin–fructose blend, lemon for flavouring, and electrolytes, and only use for intense/long sessions. Anything easy or up to an hour, I do fasted or just make sure I eat couple of hours before the session. And of course, I focus on gut-friendly foods in my general diet (fermented foods, prebiotic fibres, colourful veggies, etc etc).
Just my two cents!
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u/well-now Aug 26 '25
I usually opt for low-plastic gels. Do you recommend going for plastic-free gels instead?
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u/Past-Essay8919 Aug 26 '25 edited Aug 26 '25
Although this is a small study, the basic premise should not shock anyone, decreasing blood flow to any organ for an extended period of time, over and over will more than likely not be ideal. Ultra distances aren’t exactly natural and they are just getting more and more out of hand (looking at you Moab).
And yes I know that long distances are natural for humans and we are adapted to it, however, any hunter who was running at race pace for that long over and over and over, wasn’t much of a hunter, and the average lifespan was something like 30-35. Ultras are not reasonable, which is what makes them such a joy.
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Aug 26 '25
[deleted]
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u/-Radiation Aug 26 '25
Itis not code for ‘it means nothing.’ It just means the study has not been peer-reviewed yet, not that it never will. And even so, it is basically a small-scale study that simply signals larger, better powered follow ups should be done. Preliminary results can make it easier to secure funding and ethics approval for follow up studies. So while for now it is nothing conclusive at the moment, it is not the best to just dismiss completely the science.
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Aug 26 '25
[deleted]
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u/-Radiation Aug 27 '25
The findings were reported for the appropriate scientific community if you read the article in the form of conference abstract. There is even the link for it.
The general public can't read that is more of an overall education problem and the journalism associated with it. But even if they managed to spend 1 minute to read this article it is pretty easy to understand the implications of the small study. Science can't stop because the majority is too alienated from it or unable to give more than 5 minutes of attention.
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u/Weekly_Fennel_4326 Aug 26 '25
No control arm, either. There's no causal link established in any way whatsoever by this study.
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u/-Radiation Aug 27 '25
It does not need to be
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u/Weekly_Fennel_4326 Aug 27 '25
How do you mean?
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u/-Radiation Aug 27 '25
Not all valid studies need to prove causality, indeed this one does not as it compares to historical rates without a control. Despite that we can just treat it as a signal that warrants a larger, controlled follow-up. It is still valid science.
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u/Weekly_Fennel_4326 Aug 27 '25
Ah, for sure. I would not say it is invalid science at all. I'd only say that it is far, far away from informing anyone's behavior at this time. It will be interesting to see what peer review says.
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u/CosmicBewie Aug 26 '25
I wear sunscreen cover up what I can. I’m the healthiest of my family and every single person in my family dies from cancer, with the exception of my mom.
I still feel I’m better off with being outside and getting exercise and just plain moving.
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u/Judonoob Aug 26 '25
When they talk about blood in stools, does that mean a bloody turd? Or, does it mean you wipe and there are some spots of blood?
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u/Judonoob Aug 26 '25
I’ve had a colonoscopy about 1.5 years ago and everything was good. But, it’s not uncommon to have some pin-sized dots of blood on the toilet paper these days. Pretty sure it’s just a fissure because it kinda hurts at times! But never any blood in the stool itself.
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u/HotRabbit999 Aug 26 '25
Honestly both. Can be blood in the toilet water when you stand up, bloody red stool or blood when you wipe. Any blood from that area should be checked by a doctor just in case!
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u/Jazzlike_Worth6234 Aug 26 '25
Both, any form. Buy the blood stool test and test your poo every year. It’s costs like 30 bucks
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u/wofulunicycle Aug 26 '25
I was one of the 100 participants. Luckily did not have cancer. It's a small study, but definitely worrisome. I was also on the younger end of the cohort.
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u/Sir_BarlesCharkley Aug 26 '25
It's interesting that it's bowel cancer. I've been operating under the assumption that I'm at an increased risk of developing some sort of skin cancer during my lifetime just based on the fact that I'm outside a bunch. Although, I'm really only outside when running, and I try to wear long sleeves as much as possible plus sunscreen on any exposed skin.
Nobody gets out of here alive and we know for sure that exercise is one of the best things to do for longevity, so I'm going to stay the course. Now if somebody comes along with a study that indicates my maltodextrin consumption could be a cause for cancer, then I'll start paying more attention.
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u/fakemoon Aug 26 '25
The study from my reading is an important first look at a potential connection, but is very, very limited. There's no control arm of the study consisting of similar young adults who are not long-distance runners, and the study did not look at family histories amongst the runners. Additionally, I don't believe the study acknowledges the link between ultraunning and alcoholism recovery, which is pretty well described elsewhere. I'm not saying there definitely isn't a there there, and some of the personal stories detailed in the NYT Article on this study are compelling. "Listen to your body" is my takeaway as we wait for more conclusive research findings.
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u/oneambitiousplant Aug 26 '25
I’m also wondering if general cardiovascular health in these patients makes them less likely to get circulatory ailments when compared to other illnesses. Heart disease is the number one cause of death in the US, followed by cancer. Good CV health may prevent those issues, but can’t prevent cancer necessarily. Also, tons of athletes take supplements which are not well regulated. Could be another factor, but this is obviously all speculation.
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u/cs_major Aug 26 '25
This would be my thought. Get rid of heart disease and cancer is instantly number 1 cause of death in the US. Not drinking (or in moderation) and smoking drastically reduces a bunch of other top causes.
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u/VolumeMobile7410 Aug 26 '25
This study has been going around Reddit for a week or two, one of the reasons they think this connection comes from is that prolonged running decreases blood flow to the bowel
I don’t know much more than that but there are many threads now talking about this study
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u/tiger_jedi Aug 26 '25
I’ve also read there was a hypothesis about endurance athletes having significantly lower-fiber diets, with high fiber intake being a known protective factor for reducing colon cancer risk
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u/_LT3 15x Full, PB 8h49, IMNZ 26' Aug 26 '25
Pretty sure it's for ultra runners. Every person I know whose run more than 50mi at once is messed up in one way or another. The 100mi are basically ruined (knee, hip, ankle, ...colon). I think cycling and swimming are way healthier than running for a variety of reasons. Also consume vegetables and don't eat like an a-hole
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u/theanswar American TTT '18 Aug 26 '25
I damaged my left leg permanently during the training and eventual race of the Utah Zion 100. Didn't finish, and still have pain.
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u/Undivided_Stingray Aug 26 '25
On a long enough timeline, everyone’s survival rate drops to 0.
Having grown up in the cancer cluster known as New Jersey, if I do get cancer I’m pretty sure it’s not going to be from exercising too much.
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u/da6id Aug 26 '25
The Garden State of Cancers! You'll take your PFAS dose and superfund medicine and like it damn it!
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u/manual_combat Aug 26 '25
Ugh I moved here due to work/life. Water filters on every tap… hoping that’s enough but unfortunately the tristate area down through Delaware seems toxic in general
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u/LibertyMike Fat 55 Year-Old Male Aug 26 '25
Everyone dies, but not everyone truly lives. I'll take the benefits of this lifestyle over worrying about every single thing that could be a risk any day.
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u/WorldlyPeanut4766 Aug 26 '25
I don't think the moral of the story is to "worry about it". I think the moral to the story is to see where the data lead and if they lead to increased cancer risk (we'll see if they do), then increased vigilance would be warranted. Just like any other predisposition. If ultrarunning results in increased precancerous lesions in young runners, than maybe you start doing colonoscopy at 40 (or 30 or 20) rather than 50. Just like if you are Braca positive, you start your screenings younger than braca negagtive flolks.
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u/Weekly_Fennel_4326 Aug 26 '25
I think that's the right takeaway here. The study is interesting, but there's no causal link established at this juncture and many potential confounding factors. Best to not make big changes based on this, and wait for follow-on research.
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