&gt; <i>this study is purely associational, so cannot show whether exercise actually causes changes in telomere length, only that people who exercise have longer telomeres.</i><p>&gt; ...<p>&gt; <i>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.</i><p>Fascinating -- the first quoted sentence is logically equivalent to saying, &quot;If you have short telomeres you&#x27;re statistically unlikely to exercise much.&quot;<p>The conclusion that exercise leads to shorter telomeres is empowering and optimistic, so it&#x27;s no surprised the American scientists and press ran with it. The conclusion that people who exercise regularly are genetically predisposed to it is <i>disempowering</i>, though, and it wasn&#x27;t mentioned at all. (It is consistent with jasode&#x27;s sibling comment that exercise can speed up the ageing process, though.)<p>I&#x27;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, &quot;show me the numbers in all of the boxes and let me draw my own conclusions.&quot;