Comment by seizethecheese | Hacker News Reader

Comment by seizethecheese | Hacker News Reader

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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.

http://www.cancer.gov/about-cancer/what-is-cancer/statistics

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.

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