exercise yes, but serious endurance exercising as you get older... unfortunately generally tied to worse outcomes in most studies
Do you have any links off the top of your head? I'm interested.
sorry, forgot to check back at this thread....I apologize for what follows, apparently I wanted to say a couple of things.
Let me amend my previous comments. I should also preface this and say that my day job is that of a cardiologist (which may or may not mean I know anything). Most of the studies have been done in marathoners which are a slightly different subset that cyclists. However the changes seen on the heart are likely the same. There is no doubt that exercise is good for you. There is no doubt that exercising as you get older is extremely good for you (slows down dementia, likely decreased risk for a heart attack, slos down the inevitable progression to high blood pressure, etc..). However it is the amount and intensity which can potentially be bad for you. That being said we all have to die of something, so it is a bit of pick your poison. The other issues is what population are we talking about. I would say we are definitely talking about men older than 60, and potentially this whole thing starts to be a concern in the mid 50's (maybe).
The problem with intense endurance exercise in an older population is as follows....
1. Heart breakdown. There are numerous studies showing that a biomarker called troponin is present after endurance events which is not present prior. This marker is consequently the same one we use to detect heart attacks and signals muscle breakdown in the heart. For younger people this is fine as they can handle it. For older people this is a bit of a problem as they can actually weaken their hearts by doing long term strenuous exercise. In addition to this breakdown of heart muscle coupled with dehydration can lead to renal failure.
2. Muscle adaptation. What I really mean by this is heart muscle adaptation. There is something called "athletes heart" which is seen in most true athletes and especially in endurance athletes. It is where the walls of the heart actually get thicker in response to the increased blood pressure the heart sees from the amount of exercise that occurs. This is a necessary adaptation for the heart to be able to push the appropriate amount of blood out of it's primary pumping chamber (the left ventricle) and through the body. As one ages thickening or hypertrophy becomes more so because the pressures which are seen are actually higher than when one is younger and so the heart has to thicken more in order to accommodate this. This leads to muscle scarring or fibrosis which is generally known to be a marker of poorer outcomes.
3. Renal failure. The flow through the kidneys decreases as we get older, it is simply a fact of life. Most people over the age of 65 have a small amount of renal failure at baseline. You couple that with an endurance event which leads to dehydration and the renal failure gets worse (dehydration leads to less blood volume as blood is made up of a large amount of water, which leads to less blood flow past the kidney which leads to kidney failure). However once the flow through the kidneys decreases the body starts to build up toxic metabolites instead of getting rid of them. This then leads to a whole host of other problems. Yes this can mostly be avoided with appropriate hydration, but it is a state which older individuals are far more prone to then younger healthy athletes.
There are some other studies which have also looked at possible increase in coronary artery disease in marathon runners, but the populations they looked at were not so good, so it was pretty much ignored (and really makes no sense physiologically). Yes, there are obviously people who do very hard endurance exercise late into life and are fine. I cannot explain it except to say that genes obviously play a role in ways we dont yet understand and they are somehow able to deal with the heart adaptations which occur (or are resistant to them). However, for the general population hard endurance exercise late into life has led to bad outcomes in several studies. Cant find them off the top of my head, if and when I do I will post them. I dont think we know enough to say exactly who it has led to bad outcomes for, which is why I still occasionally do 150 mile events with my father who is >65yrs old.
Although I hate getting scientific data from the new york times they actually sum it up relatively well in a small series of articles which I will link to below. I will also include some links to a couple of scientific studies.
NY times articleshttp://well.blogs.nytimes.com/2009/09/30/phys-ed-how-do-marathons-affect-your-heart/http://well.blogs.nytimes.com/2011/03/09/when-exercise-is-too-much-of-a-good-thing/