Observational studies have demonstrated that exercise delays (prevents) dementia to at least some degree. We will all run more confidently on the road to dementia free old age when there are randomized clinical trials that show what the observational data suggest. ( In the interest of complete disclosure I am a marathon runner and only a recalcitrant biceps tendonitis ( the biceps in the leg) kept me from running my 29 Houston marathon in a row in January.
A recent issue of the Annals of Internal Medicine has the latest data . A discussion of this and similar articles must include comments about the concept of "reverse causation". We observed those old folks ( now known as seniors) who exercised regularly had a lower attack rate of dementia. There have been similar studies showing that those folks who are more socially engaged, or more active in mental activities (cards, games,cross word puzzles etc) seem less likely to develop dementias.One explanation could be that something about the early phases of dementia may cloud their judgment or confidence or some combination of cognitive impairment may appear so that they withdraw from of all manner of activities including regular exercise.
Still, those of us who are obsessed exercisers like to think our plodding along generates or releases some sort of hormones or cytokines or something that is neuroprotective.