While I run because it’s what I do, I like being in shape simply as a general proposition and am as vain about it as the next guy. I understand that exercise may not extend one’s life-span but that it can improve the quality of life in our later years. Here’s a further explanation (from LetsRun): “How Exercising Keeps Your Cells Young

A study suggests that running 50+ miles a week is good on the cellular level.

    Even more striking was what was going on beneath those deceptively youthful surfaces. When the scientists examined white blood cells from each of their subjects, they found that the cells in both the active and slothful young adults had similar-size telomeres. Telomeres are tiny caps on the end of DNA strands — the discovery of their function won several scientists the 2009 Nobel Prize in medicine. When cells divide and replicate these long strands of DNA, the telomere cap is snipped, a process that is believed to protect the rest of the DNA but leaves an increasingly abbreviated telomere. Eventually, if a cell’s telomeres become too short, the cell ‘‘either dies or enters a kind of suspended state,’’ says Stephen Roth, an associate professor of kinesiology at the University of Maryland who is studying exercise and telomeres. Most researchers now accept telomere length as a reliable marker of cell age. In general, the shorter the telomere, the functionally older and more tired the cell.

    It’s not surprising, then, that the young subjects’ telomeres were about the same length, whether they ran exhaustively or sat around all day. None of them had been on earth long enough for multiple cell divisions to have snipped away at their telomeres. The young never appreciate robust telomere length until they’ve lost it.

    When the researchers measured telomeres in the middle-aged subjects, however, the situation was quite different. The sedentary older subjects had telomeres that were on average 40 percent shorter than in the sedentary young subjects, suggesting that the older subjects’ cells were, like them, aging. The runners, on the other hand, had remarkably youthful telomeres, a bit shorter than those in the young runners, but only by about 10 percent. In general, telomere loss was reduced by approximately 75 percent in the aging runners. Or, to put it more succinctly, exercise, Dr. Werner says, ‘‘at the molecular level has an anti-aging effect.’’

Separately, a long-term study by Paul Williams at Lawrence Berkeley National Laboratory also suggests the benefits of doing more than just the minimum. There’s an article in the San Francisco Chronicle: “More exercise better in long run, study finds”

[Edited to add: I took a look at the comments to the Times piece and there were a good many I’d-rather-die-a-painful-and-horrible-death-before-I’d-go-for-a-run observations. My comment:

    I skipped over the comments in the middle, but I was saddened by those who view exercise — running i particular — as a chore. Sure it can be boring, but for some of us it is a passion, and evidence (we’ll see if it is established) of long-term health benefits is a perk.

    I’m 53, have been running for 39 years, and got in about 47 miles last week. I run because I love it, and am hardly unique in this, as a look into the blogosphere and on message boards will readily show. I train hard and race hard, and while I may not enjoy every step, I wouldn’t give any of them up for the world.

    But, as I say, I feel truly sorry for those who don’t share this, or who don’t become involved in some other sport.]