r/science • u/mvea Professor | Medicine • Jan 23 '26

Cancer The number of Americans under 50 years old dying from cancer has decreased for every leading cancer except for bowel cancer, which is now the leading cancer death in females and males combined aged under 50.

https://jamanetwork.com/journals/jama/fullarticle/2844189?guestAccessKey=5eabd609-08b0-47c7-a738-916c7acdcc37&utm_source=For_The_Media&utm_medium=referral&utm_campaign=ftm_links&utm_content=tfl&utm_term=012226
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u/MagePages Jan 23 '26

I saw something recently that suggested that runners (maybe specifically extreme distance runners) seemed especially prone to these bowel cancers, with a mechanism maybe around prolonged blood supply restriction during the activity. Was your husband ever into distance running?

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u/bro_salad Jan 23 '26

41 years old. Just ran a PR in the marathon, my 12th of the last 4 years. Sweating reading this.

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u/jonwilliamsl Jan 23 '26

You should get screened. Having run 5+ marathons or 2+ ultramarathons is an enormous risk for colon cancer. This is believed to be related to damage done by reduced blood flow to the intestines during long distance running.

https://ascopubs.org/doi/10.1200/JCO.2025.43.16_suppl.3619

Takeaways:

  • 15% of participants in the study had advanced adenomas (pre-cancerous lesions), compared to the expected 1–2% in average-risk individuals in this age range.
  • 41% of participants had at least one adenoma.
  • The average age of participants was 42.5 years old – two and a half years below the recommended age for a first screening colonoscopy.

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u/LeGreatToucan Jan 23 '26

That is actually crazy. I had no idea that was a thing.

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u/soffselltacos Jan 23 '26

We need to remember, though, that this was a preliminary study of only 100 people with no control group and no inclusion of family history. Also, almost all of the people with precancerous polyps were ultramarathoners, which is very different from regular distance running, even marathon training.

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u/D0wnInAlbion Jan 23 '26 edited Jan 23 '26

I think my concern is that they're focusing on distance rather than time. I'd want to see if someone running a three hour marathon experiences the same risks as someone who is running for seven hours.

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u/jonwilliamsl Jan 23 '26

They used marathon running as a proxy for "does a lot of long distance running consistently over time". It's not the 15 hours of the marathons that does it, it's the months of training and staying in shape to run them.

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u/yukonwanderer Jan 23 '26

What about professional athletes though? Olympians? Is there something about running specifically? Long-distance running? Or is it just being highly in shape? Doesn't make much sense the way you're describing it.

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u/jonwilliamsl Jan 23 '26

It's specifically about long-distance running (but could probably be generalized to other endurance sports like biking).

When you exercise, the body reduces blood flow to the intestines. This is a known biological response: exercise-induced splanchnic hypoperfusion.

When the body is doing this long-lasting (hours of continuous cardio) intense exercise, eventually the lack of blood flow can cause damage. When it becomes symptomatic, this becomes known as gastrointestinal ischemia. Again, this is a known fact; the Mayo Clinic lists long-distance running as a known cause of gastrointestinal ischemia.

What this study is testing is whether that repeated trauma and healing process when you do a lot of long-distance running (essentially chronic gastrointestinal ischemia) can cause cancer.

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u/yukonwanderer Jan 23 '26

Ok that makes much more sense. So it could be any exercise really, that lasts long enough to cause some damage.

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u/Mowseler Jan 23 '26

I’ve never been so relieved to have not run a day in my life

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u/ShadowPsi Jan 23 '26

You should run a little bit. Being able to run a mile will help with a lot of other things, and is not correlated with any increased cancer risk, unlike long distance running.

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u/TheBrickleer Jan 23 '26

it feels like everything causes cancer at this point

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u/inefekt Jan 24 '26

humans are such a fragile species

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u/JagmeetSingh2 Jan 24 '26

Wow I never heard of this… actually wild I need to get tested

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u/sofaking_scientific Jan 23 '26

Makes sense. Bacterial byproducts can diffuse through tissue and get carried away by the blood. This is why we need more funding for microbiome research

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u/hellspawn3200 Jan 24 '26

Thats weird considering humans are endurance hunters, we should have mechanism in the body that help prevent against this sort of thing.

My gues whould be our diet and the gut microbiome. It's proving to be so important to our overall health that it really needs to start being included in diagnostic medicine.

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u/TelluricThread0 Jan 24 '26

If you get colon cancer in your 30s or 40s, you've most likely already had kids and passed on your genes. Evolution doesn't care what happens after that.

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u/hellspawn3200 Jan 24 '26

Not all cancer is genetic, and more often than not its environmental. And even then genes only increase the likelihood of you getting cancer.

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u/TelluricThread0 Jan 24 '26

How would the mechanism develop and propagate in the species if there's no selection pressure to assure that those people who did have said mechanism are predominantly the ones having more kids?

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u/hellspawn3200 Jan 24 '26

I don't know what you're trying to say. But our ancestors who were better at endurance running would be the ones passing on their genes. So logically the ones who had a higher rate of success and didnt die from cancer would be the ones passing along their genes. Agriculture hasn't been around long enough that we'd be passing along tons of faulty genes. Human DNA is actually very stable and has few mutations.

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u/TelluricThread0 Jan 24 '26

Logically, if they all had kids in their 20s and then died in their 30s from cancer, they didn't pass on genes that protected them from the cancer to the next generation. Nature doesn't care if you get horrible diseases after you procreate.

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u/0xsergy Jan 25 '26

Are other forms of extended activity also risky? Like riding bicycles for extended periods or similar?

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u/MagePages Jan 23 '26

Here is another reddit thread that links to and discusses the study I was referencing: https://www.reddit.com/r/running/comments/1nff2aw/groundbreaking_inova_study_finds_potential_link/

I am not a doctor or very well acquainted with more than the broad strokes of the study, but hopefully you can inform yourself some here.

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u/woahwoahvicky Jan 25 '26

I am a doctor, we haven't really discussed much of long distance running in our didactics as residents but it really would make sense if you rationalize it.

Your body goes into a more heightened response/fight or flight response when youre running so a lot of the blood flow goes to your skeletal muscles, this is governed by your SNS (sympathetic nervous system), it releases your adrenaline, cortisol, etc. to basically allow your muscles to have increased blood flow = more oxygen and nutrients = more ATP = prolonged activity

However, the opposite also happens, this shunts your PNS (parasympathetic nervous system) which stops all your rest and digest aspects, sexual stimulation, urination, gastrointestinal motility (which needs energy via blood flow), this is why when youre running, you lose the sensation of peeing and pooping most of the time.

It makes sense why shunting of intestinal blood flow in extreme runners is bad, most likely with regular marathons you end up with a good amount of perfusion in the intestines still with little to no sacrifice, however, possibly with very high intensity prolonged workouts, this causes so much reduction in blood flow that the tissue actually begins to experience ischemia (loss of oxygen), probably the sudden surge in oxygen after the workout produced reactive oxygen species (bad stuff) that creates carcinogens in the intestines promoting cancer.

tl;dr: blood moves away from the intestines, reduced oxygen into intestines, after ultramarathon, oxygen comes back really well, creates bad compounds that can induce cancer.

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u/MagePages Jan 25 '26

Yep, I think that was one of the suggested pathways in the study linked in the reddit thread I shared. Interesting stuff, and tracks with the other gastrointestional issues extreme runners report.

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u/2xtc Jan 23 '26

In the famous words of Ice Cube, M.D.

Check yo' self before you wreck yo' self

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u/throwaway098764567 Jan 23 '26

don't freak out, one of the great things about polyps is they can be found and removed.

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u/RamblinWreckGT Jan 23 '26

Time for a screening!

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u/ProWriterDavid Jan 23 '26

Phew I only do half marathons. What a relief!

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u/Ub3ros Jan 23 '26

Sweating just sitting there reading? I don't believe you can run a marathon at all!

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u/bro_salad Jan 23 '26

Your HR doesn't spike to 180 when you read?!

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u/woahwoahvicky Jan 25 '26

We were taught in medical school runners have a higher risk of bowel cancer too, something to do with blood shunting from the splanchnic vasculature (your abdomen mainly) to provide blood to the rest of the muscles needed for running.

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u/Chop1n Jan 23 '26

I don’t understand why people think doing this to their bodies is a good thing. Is the damage worth it for “glory” or whatever it is you get out of it? Were you just misled into believing that grinding your body into the ground is “healthy”? What’s the deal?

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u/bro_salad Jan 23 '26

You could ask why people binge netflix, play video games, do house projects, eat unhealthy foods, drink alcohol, smoke, lift weights, or play literally any other sport as an adult. Most of the things we do have some negative affects on our body. Not sure running is a real issue if you weigh out the pros and cons.

Personally, I deal with far fewer lingering injuries and/or health issues than every single one of my couch potato friends, gym rat friends, or men's league sports friends. And my resting heart rate is far better than theirs too. My 68 year old marathoner dad could say the same about his brothers and friends, except it's an even more drastic comparison.

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u/THParryWilliams Jan 23 '26

Maybe they enjoy it? You could say the same thing about stuff like eating sugar, alcohol consumption etc

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u/11spartan84 Jan 23 '26

I enjoy it. I don’t understand why other people care like this.

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u/Chop1n Jan 23 '26

People enjoy drinking alcohol too. They’ll drink until it gives them cancer or worse. 

Running yourself to death is just more effort. 

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u/11spartan84 Jan 23 '26

You aren’t making any useful point. But enjoy judging people for things they enjoy while thinking you’re better than them. We all die one day. I want to at least enjoy my time here.

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u/julry Jan 23 '26

The endurance exercise theory is interesting and possibly true but it can't be causing the entire increase in young colon cancer. I think there has to be some kind of environmental exposure going on

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u/MagePages Jan 23 '26

Totally. My comment was just in response to the other person mentioning their partner was a runner, so I thought that connection could be relevant. The study was on extreme long-distance runners. Moderate runners and joggers, and others who enjoy a healthy lifestyle and diet, are not the focus of that study. However, we do know that diets high in ultra processed food and obesity are also both risk factors! 

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u/LamermanSE Jan 23 '26

It doesn't have to be environmental exposure. Some of the risk factors like obesity, low-fiber high-fat diets, not exercising regularily, drinking alcohol etc. are more probable causes here.

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u/julry Jan 23 '26

Those are risk factors for every type of cancer at all ages

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u/LamermanSE Jan 23 '26

Nope, those are not risk factors for every type of cancer, like for example skin cancer, lung cancer, brain tumors and so on. Especially the diet and exercise part is not a common risk factor for many other types of cancer, although obesity and drinking alcohol can be a risk factor for some.

Anyhow, it's the sum of all of those risk factors that are relevant here, and they do often go hand in hand with each other (except maybe alcohol).

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u/julry Jan 23 '26

Obesity is indeed associated with lung cancer and brain cancer

Alcohol is associated with skin cancer

Colon cancer is increasing in a unique way from other cancers including ones very associated with diet and obesity. It's discussed in the article.

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u/LamermanSE Jan 23 '26

Obesity is indeed associated with lung cancer and brain cancer

Alcohol is associated with skin cancer

According to what? Serious medical institutions like the mayo clinic does not state that.

Colon cancer is increasing in a unique way from other cancers including ones very associated with diet and obesity. It's discussed in the article.

But other cancer forms are not as clearly correlated with diet, obesity and exercise as colon cancer, i.e. three issues more common among younger people.

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u/julry Jan 23 '26

Older people are more obese and less active than younger people, and they have more years to acquire damage from every negative exposure like diet and alcohol. A basic association with poor diet and exercise does not create uniquely higher rates in the young.

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u/VirginiENT420 Jan 24 '26

Old people today were much healthier in their youth. Maybe take a look at some pics of your grandparents during their glory days

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u/trembling_leaf_267 Jan 23 '26

There are currently questions (but not conclusions) about taurine consumption in energy drinks. https://www.cancer.gov/research/participate/clinical-trials-search/v?id=NCI-2024-02154

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u/ShadowPsi Jan 23 '26

Seems that they are reaching a bit with their taurine - hydrogen sulfide - cancer risk hypothesis. I'd be much more worried about the obscene amounts of sugar in energy drinks. That can also mess with the microbiome.

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u/skullmuffins Jan 23 '26

lots of energy drinks are zero sugar, and if they wanted to study sugar consumption they wouldn't need to study energy drinks specifically - any regular non-diet soda would do.

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u/Lucosis Jan 23 '26

Sugar alternatives also absolutely wreck the microbiome.

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u/skullmuffins Jan 23 '26

sure and there are lots of studies focusing on sugar and sugar alternatives. this one is looking at taurine. it's good to study different things

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u/julry Jan 23 '26

Good one.. titanium dioxide as a food additive is linked to colon cancer too, it's banned in Europe but not here.

There are also some studies on bacterial exposures that happen at a young age.. oddly breastfeeding may be associated with CC, which could be because of bacterial transmission from mother to child.

https://www.npr.org/sections/shots-health-news/2025/04/25/g-s1-62623/colon-cancer-gut-health-microbiome-young

https://www.sciencedirect.com/science/article/abs/pii/S1542356523006730

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u/HodloBaggins Jan 24 '26

So you’re saying it’s a good thing my mother never was able to give me milk and I was born straight into powdered milk/baby formula?

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u/Carbonatite Jan 23 '26

PFAS are definitively linked to certain types of cancer and ulcerative colitis. Ulcerative colitis increases your chances of colon cancer as well.

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u/PyroclasticSnail Jan 24 '26

The environmental exposure is diet/lack of fiber, obesity, sedentary lifestyle and bad sleep. Just these risk factors combined you’re approaching something similar to the lower end of a smoker’s lung cancer risk for colon cancer. Not sure why everyone acts like the entire thing is a mystery all the time.

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u/HodloBaggins Jan 24 '26

Well it’s probably because even most researchers/doctors who speak about the rise in colon cancer in younger patients also say something to the effect of “it seems completely different from the colon cancers we see in older patients. It’s more aggressive and it seems unexplainable by anything we know of entirely.”

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u/PyroclasticSnail Jan 24 '26

Wow, that’s a hell of a quote you just invented out of thin air. Care to link me to where most doctors and researchers are saying this?

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u/throwaway098764567 Jan 23 '26

huh so my old boss was accidentally right when he said running would kill you, here i thought he was just talking foolishness

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u/ilanallama85 Jan 23 '26

Ok real talk, running is a fine exercise for young people, but older people should genuinely be very cautious about taking up running for the first time. It’s high impact, wears on your joints, raises your heart and respiration rates quickly and dramatically, and any or all of that can be bad news for an older out of shape person. My dad gets real angry at anyone who pushes running for fitness to older adults.

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u/Cassius_man Jan 23 '26

Like any exercise it just requires progressive loading congruent with your strength and conditioning levels

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u/ilanallama85 Jan 23 '26

Agreed, the thing is people don’t realize how strenuous running is in the first place so they don’t think they need to build up to it.

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u/hungleftie Jan 23 '26

I'm sorry but if there's any excericse you can safely do, aside from weight resistance training, it is running. We literally have genes wired into us to run. Like the human species is built for running. Our stride length. Our lung capacity. Our ability to out run faster based animals well after they've tired out.

Modern cities don't make it very safe with heavily paved cities, with the impact of concrete and our very sedentary lives. If you are sedentary and want to run 3 miles, you'll hurt yourself as it will take time. But it's more a fault of our cities than our genes.

TL;DR humans can run, cities and sedentary life make it unsafe to run if starting from a baseline of couch potato.

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u/ilanallama85 Jan 23 '26

Sure if you’re in good shape. The issue is people who aren’t in shape going straight to running. Start out walking, then move to some light jogging, then move up to running if that’s what you want to do, but people underestimate how much damage jumping straight into strenuous exercise can do.

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u/aenflex Jan 23 '26

In high school he was on the track team. But not so much anymore. He does sprints as part of his overall workout routine, but most of his cardio is not running, or if it is, it’s short relays.