My pet theory is that high performance athletes who train intensively
tend to live shorter lives than the average life expectancy.  Any
support for this?

There is some support for your hypothesis, however, it looks as if the
studies done to date are insufficient to make a definitive
determination.

For example, Dr. Kim Chong-in of Wongwang University conducted a life
span survey using newspaper obituaries of for some 2,100 people
between 1963 and 2000.

He discovered that athletes ranked 9 out of 11 for life span.

http://home.donga.ac.kr/~daudh/magazine/118/bitter.htm

Then there's the theory that high protein diets required by intensive
training contribute to shorter life spans. This article, not quite on
point, spells out the issue.
http://www.nytimes.com/books/01/02/11/reviews/010211.11brubact.html

''Nutritionists agree that even average Americans consume twice as
much protein as they need; bodybuilders take in 20 to 30 times too
much, and high-protein intake can drastically shorten life span,'' she
alleges, evidently oblivious of the extreme demands that hypertrophy,
the process of increasing muscle mass, makes on the body. In fact, the
elevated protein requirements of athletes engaged in intensive
strength training have been well established by sports medicine
research, and standard formulas exist."

If athletes do not follow the standard formulas, they could be harming
their bodies. There's also the issue of steroid use, which would also
decrease life-span (on the average).

Finally, consider this article in life extension magazine. It says
there are not enough scientific studies to state a correlation between
exercise and an extended lifespan. However, the author also notes,

"I believe many athletes may actually shorten their lifespans due to
the high intensity with which they train. Intense training is a
necessity in competitive sports but the frequency of training
sessions, and the lack of recuperation time between sessions, is not
adequate enough to repair damage from overly heavy training."

Can Exercise Extend Lifespan? By John Abdo Fitness Trainer
http://www.lef.org/magazine/mag96/feb96-fitness.html

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