I read articles tonight about top calibre fitness people who are relatively young (20's) being diagnosed with cancer despite checking off all of the marks for a healthy lifestyle.
What could be causing the cancers in their cases?
Post a link to the article(s). I'm not aware of a disproportionate number of elite athletes getting cancer.
That said, exercise is both good and bad for cancer. Mostly, it's good, but there are some situations when it can be bad.
Simplified... exercise creates free radicals as a byproduct. The immune system eats them up. You get stronger; your immune system gets stronger.
However, at some point, extreme ongoing exercise or more likely, extreme ongoing exercise combined with stress, poor genetics, chronic inflammation, an illness, or environmental pollution creates a situation where the immune system cannot respond fast enough and weakens over time.
Everyone, including every reader of this post, has cancerous cells in their bodies. Our immune systems destroy these damaged cells before they can reproduce. If the immune system is weakened over time, these cancerous cells can reproduce, forming tumors, etc.
What does that mean for runners?
Overwhelmingly, runners are healthier than their sedentary peers.
However, in my opinion, seriously competitive marathoners over age 50 are at a greater risk of diseases compared to their recreational runner peers.
My circle of senior runners who are seriously training seem to have a higher prevalence of diseases linked to weakened immune systems compared to their recreational runner peers. I do not see the same trend in elderly sprinters and middle distance runners who run less than 15mpw.
This evidence is purely anecdotal, but it was convincing enough for me to stop marathon training in 2001 to pursue shorter distances.