&#62;<i>"Everything else I've ever read says exercise is dwarfed by diet when it comes to health, and the health benefits are pretty minimal to fitness beyond a pretty low threshold"</i>
&#60;citation needed&#62;<p>We've already been over this ground more than once:<p>According to one 32,000 person study in the American Journal of Clinical Nutrition (1999), "fit persons with any combination of smoking, elevated blood pressure, or elevated cholesterol level had lower adjusted death rates than low-fit persons with none of these characteristics". The same study found that aerobic fitness had a far more important impact on longevity than obesity did.
This was cited in <i>Fantastic Voyage, Kurzweil and Grossman, Chapter 22.</i><p>Another 100,000+ person study found that men who ran two or more marathons per year were 41 percent less likely to suffer from high blood pressure, 32 percent less likely to have high cholesterol, and 87 percent less likely to be diabetic than non-marathoners. Those who ran only one marathon every two to five years also had significantly lower risk for these conditions than non-marathoners.
<a href="http://www.medicalnewstoday.com/articles/140104.php" rel="nofollow">http://www.medicalnewstoday.com/articles/140104.php</a><p>Here's a different piece on how regular hour-long runs stimulate neurogenesis and memory improvements in middle aged humans:
<a href="http://www.dana.org/news/brainwork/detail.aspx?id=7374" rel="nofollow">http://www.dana.org/news/brainwork/detail.aspx?id=7374</a><p>Distance running is one of the most beneficial things you can do for yourself. Racing marathons is also fine, with sufficient training.