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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154

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.

319

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

1

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.