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Exercise Tied to Lower Risk for Some Types of Cancer (well.blogs.nytimes.com)
104 points by hvo on May 19, 2016 | hide | past | web | favorite | 54 comments

I don't have access to the actual paper, but my first thought on this is to wonder if they factored in the idea that people who specifically exercise are obviously interested in being healthy and may be doing other things that are "healthy" that would affect whether they get cancer or not.

I wonder if it'd be possible to get data on people who are active, but not for the reason of being healthy, things like working construction, and compare that to see if it's the activity itself or just the mentality that comes from wanting to be healthy.

From the article: Encouragingly, the associations between exercise and reduced cancer risks held true even when the researchers factored in body mass. People who were overweight or obese but exercised had a much lower risk of developing most cancers than overweight people who did not move much.

This is directly related to a comment I posted on another article two days ago[0].

This may seem more surprising than it actually is, because by "overweight" and "obese" they are referring to BMI categories, according to the abstract. The overweight BMI category contains people who range from healthy, lean and muscular (think muscular gym goer) to people who have little muscle mass and high body fat percentage (think large beer belly). The fact that you can decrease cancer risk by gaining muscle (usually from increased exercise, precisely the thing being studied) and losing fat while maintaining the same physical mass and thus the same BMI, is not shocking.

Once you control for body fat, having additional muscle mass (thus higher BMI) probably decreases all-cause mortality.[1]

Unfortunately, I don't think this has much bearing on azdle's questions, since people can be fit for many reasons, either by intent or by necessity.

0: https://news.ycombinator.com/item?id=11714249 1: http://annals.org/article.aspx?articleid=2499472

Here's the problem with your idea though http://www.npr.org/templates/story/story.php?storyId=1779251...

It suggests people get more benefits from exercise when they expect it.

I'm curious to hear your thoughts.

That's a very interesting experiment, however, at least from how it's described in that article, I don't think it's anywhere rigiorus enough to draw any conclusions from.

> One possible explanation is that the process of learning about the amount of exercise they were already getting somehow changed the maids' behavior. But Langer says that her team surveyed both the women and their managers and found no indication that the maids had altered their routines in any way. She believes that the change can be explained only by the change in the women's mindset.

I think that they're too quick to dismiss a change in behavior. Simply asking someone (and their managers‽) if they did anything different this month than they did last month isn't a very reliable way to figure out if there were any subtle changes in behavior.

I don't know if they were expecting massive conscious changes, but I would be shocked if suddenly knowing that their daily routine is good for them didn't change some of the subconscious decisions they were making. Even just simple things like taking the stairs 10% more than they did before or how they decide when and how much to eat based on a certain level of hunger. You're still going to think "I took the stairs sometimes, but took the elevator when I needed it." or "I ate the same foods that I did before." but maybe you were taking smaller portions.

Basically what I'm trying to say is that it's very hard to draw hard quantitative conclusions from vague qualitative assessments.

It's an interesting idea, but it would really need to be explored further. There's many things I see as variables that could cause the effect with the house maids, like an overly broad definition of house maids, or wrong assumptions about the type of exercise they get.

What about people who exercise because they want to look ripped? I've known all sorts of people who exercise but live otherwise unhealthy lifestyles. They're not doing it for their health, but for appearance.

I think the only problem is the careers that have the most physical activity seem to be the most dangerous or prone to drug use.

Firemen, military, police, construction have high death rates. Atheletes have drug problems.

Not all physically active careers are dangerous. Off the top of my head I can think of mail carrier, garbage collector, movers.

Results from the source study abstract[1]:

" A total of 1.44 million participants (median [range] age, 59 [19-98] years; 57% female) and 186 932 cancers were included. High vs low levels of leisure-time physical activity were associated with lower risks of 13 cancers: esophageal adenocarcinoma (HR 0.58, 95% CI 0.37-0.89), liver (HR 0.73, 95% CI 0.55-0.98), lung (HR 0.74, 95% CI 0.71-0.77), kidney (HR 0.77, 95% CI 0.70-0.85), gastric cardia (HR 0.78, 95% CI 0.64-0.95), endometrial (HR 0.79, 95% CI 0.68-0.92), myeloid leukemia (HR 0.80, 95% CI 0.70-0.92), myeloma (HR 0.83, 95% CI 0.72-0.95), colon (HR 0.84, 95% CI 0.77-0.91), head and neck (HR 0.85, 95% CI 0.78-0.93), rectal (HR 0.87, 95% CI 0.80-0.95), bladder (HR 0.87, 95% CI 0.82-0.92), and breast (HR 0.90, 95% CI 0.87-0.93). Body mass index adjustment modestly attenuated associations for several cancers, but 10 of 13 inverse associations remained statistically significant after this adjustment. Leisure-time physical activity was associated with higher risks of malignant melanoma (HR 1.27, 95% CI 1.16-1.40) and prostate cancer (HR 1.05, 95% CI 1.03-1.08). Associations were generally similar between overweight/obese and normal-weight individuals. Smoking status modified the association for lung cancer but not other smoking-related cancers."

[1]: http://archinte.jamanetwork.com/article.aspx?articleid=25218...

Phew, 186 thousand cancers included out of 1.4 million participants? I knew cancer was not entirely uncommon but... man. That's a lot of unhappy news. Feels bad to think about.

If it is true that exercising regularly reduces the risk of cancer, I wonder what the mechanism is? Exercise builds muscle mass, improves lung capacity... Why would that have anything to do with cancer?

>Phew, 186 thousand cancers included out of 1.4 million participants? I knew cancer was not entirely uncommon but... man. That's a lot of unhappy news. Feels bad to think about.

2 out of 5 will get cancer during their lifetime.


And close to 50 percent once uou cross the 80s. The biggest factor for cancer is aging.

I remember as a kid I used to play soccer 1 hour bike away from home. One week I had a bad flu, but I decided to go anyway. The next day I felt mostly cured. I expected that exhaustion (2 hours biking + 2 hours somehow intensive soccer amongst PE teachers .. really exhausting) would worsen the disease but it did not.

Few times since I could notice that in lesser scales.

Maybe increase blood flow, increased metabolism, endorphins, etc do help keeping your system active instead of going in suspend mode while the immune system reacts alone.

Just yesterday I had this metaphor of biology being a gyroscope, the more it spins the more it can dodge.

It's conjectured that fasting kills (pre)cancerous cells by basically starving them when they fail to downregulate their metabolism under a calorie deficit. Perhaps exercise could have a similar effect in diverting energy from higher-cancer-rate cells (skin, digestive tract linings, endometrium, etc.) to lower-cancer-rate cells (muscle cells)?

Doesn't that just mean that people who have cancer (and maybe don't know it) don't really feel like exercising?

I'd guess it doesn't really prevent cancer so much as boost your immune system so it can eliminate early tumors.

>> (HR 0.58, 95% CI 0.37-0.89)

Can someone explain the numbers? I read it as risk, sub-population, error margins. Is that right?

HR stands for Hazard Ratio. 0.5 would mean something is half as likely as for the control group, while 2 would mean twice as likely.

0.37-0.89 is the confidence interval at 95% confidence. So it's expected that if the study were repeated many times, the HR would appear to be within that (rather wide) range 95% of the time. This time it's 0.58.

The main thing is that the upper bound 0.89 is quite a bit less than 1, so you could pretty confidently say there's a reduced risk, even if the amount is uncertain.

Thanks for clarifying.

No. This study is confounded and provides no evidence of anything.

The problem is that people's willingness to exercise depends on their health as much as or more than their health is affected by exercise. Because this study did not involve an intervention (it just pooled a bunch of surveys), it can't distinguish between exercise causing reduced cancer risk, or a third variable affecting both.

I can attest to that. I had weaker health a few years ago (lack of activity mainly) but I could kick a regular schedule of activity to get back on track. An accident broke my health below the self help threshold. When you're worried you can't jog, even walk, it's hard to bootstrap the exercice-health cycle again.

The same could be said of almost any study that tried to show this. It is unethical to design the study in the way you're suggesting (i.e. stop people exercising to see if they get cancer).

They did however:

> Body mass index adjustment modestly attenuated associations for several cancers, but 10 of 13 inverse associations remained statistically significant after this adjustment.

So even for two thin people, exercise seems to have helped. I legitimately don't see how you could design a study that you'd be satisfied with.

The correct study is one where some participants get an intervention to make them exercise more, and some are left alone. There's no ethical issue, but running such a study would be difficult and expensive.

Adjusting for BMI does not solve the problem, because there are many things besides BMI (unmeasured confounders) which affect both cancer risk and willingness to exercise.

And BMI is a pseudo science measure anyway. Its been proven to be a poor indicator in about every disease many times before.

the problem is that on noisy data, that adjustment of the variables isn't really as statistically clean as maths would say.

it's the same with red meat causes cancer studies. they say they remove smoking and lack of exercise and still wave the statistical significance.

it's very questionable how they removed the influence of these variables, since meat eaters do smoke way more, and do not exercise, and care about their health less.

Actually, I think noise is a red herring, and that worrying about noise (instead of worrying about unmeasured confounders and incorrect causal structures) is how epidemiology got into this mess in the first place.

Statistically significant does not prove anything, and it does not mean the difference would be large either.

An interventional study is ideal, but unlikely to happen.

I would have been happy if the authors just tried to factor in other characteristics like socioeconomic status, education level, etc. It looks like they didn't do that but instead just observed an "association" which isn't terribly interesting or informative.

I will add that this is the sort of thing that peer review theoretically ought to stop, or at least force authors to include caveats for. Unfortunately, studies with this sort of methodology make up most of the so-called studies published, so they can't really do that.

I haven't read the paper itself, but even if it didn't explicitly note these caveats, it would be assumed by any reader in its intended audience.

The problem is the press representation of the papers as something they're not.

These types of papers should be published, because they are necessary to decide which hypotheses to test with interventional studies.

John Oliver pointed out that the media usually distorts what the studies say. He failed to flag the problem of junk science in high-prestige journals.

(Edit: I just re-watched his segment. He does talk about P-hacking and perverse incentives, which is at least a reasonable-size chunk of the problem, just not the failure mode for this particular study.)

I still agree with you, he did not place enough of the blame on scientists who are unable or unwilling to properly communicate the implications of their work.

I think it's pretty obvious. I believe that it is not that exercise helps, but sedentarism is poisonous. A sedentary 40 year old looks and feels 20 years older than a 40 year old athlete.

Agreed, but it can't be as simple as merely sitting down. For example, sitting down for meditation is considered healthy, and may in fact be so.

Healthy for the mind, sure. For you cardiovascular system? I doubt it.

>A sedentary 40 year old looks and feels 20 years older than a 40 year old athlete.

This is a completely unsubstantiated claim.

you want a randomized study? :D

Yes, how about taking pictures of a bunch of 40 year old marathon runners and putting it next to a picture showing a bunch of 20 year old overweight accountants and then ask people to guess the average age of each group? That should be pretty simple and covers at least the "looks" claim.

actually a 40yr old athlete that has already more than 20 year of athlete life behind will have a body in a much more bad shape than a guy who had regular walks and healthy diet.

I'm talking about a healthy athlete, not one that it's into professional sports and actually destroys his body or hearth with substance abuse.

This depends greatly on what type of sport was practiced for 20 years.

Risks are often affected by your genetic makeup, eating and exercising habits, where you live, what type of work you do, and childhood exposure to harmful materials. There are other things that influence the risk level.

Personally, staying informed and listening to my body has been my best medicine, but I'm also aware of my family history with different diseases, which helps shape my choices.

It would be interesting to see whether or not one could show that exercise is tied to higher risk for some types of cancer if they would use the same methodology analogously.

This article is poorly written. The term 'tied' is correct in the title since its an observational study, but then it jumps directly into implying a causal relationship based on the correlation. Correlation is not causation.

Drink hot water and go for one hour early morning walk;

why hot water, I read that cold water burns some calories as well?

> I read that cold water burns some calories as well?

Not very many. An 8oz cup of water at 40F burns 2.1 calories to warm up to body temperature.

20 percent less between super active folks and non active ones is not super convincing. If it diminished the risk by 80 percent instead it would make for a much better story

>>20 percent less between super active folks and non active ones is not super convincing.

Do you mean "compelling"? Because it should definitely be convincing: it's well outside the margin of error.

Yeah, compelling is what I meant.

Not even going to read this but cancer is pure environmental and can be avoided. some people get exposed to things and it sucks. yeah eat healthy and move spontaneously.

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