> this study is purely associational, so cannot show whether exercise actually causes changes in telomere length, only that people who exercise have longer telo

> this study is purely associational, so cannot show whether exercise actually causes changes in telomere length, only that people who exercise have longer telomeres. > ... > So the message seems clear, he says. “Exercise is good” for your cells, and “more exercise in greater variety” is likely to be even better. Fascinating -- the first quoted sentence is logically equivalent to saying, "If you have short telomeres you're statistically unlikely to exercise much." The conclusion that exercise leads to shorter telomeres is empowering and optimistic, so it's no surprised the American scientists and press ran with it. The conclusion that people who exercise regularly are genetically predisposed to it is disempowering, though, and it wasn't mentioned at all. (It is consistent with jasode's sibling comment that exercise can speed up the ageing process, though.) I'd also be interested in the inverse correlation -- are sedentary lifestyles associated with shorter telomeres? What proportion of people in the study actually did exercise, and what proportion had shorter telomeres? Essentially, "show me the numbers in all of the boxes and let me draw my own conclusions."