Exercise in middle age prevents stroke in old age         People who exercise regularly from the age of 40 are less likely to suffer brain damage and shrinkage of the vascular network at the age of 70 and older.       increasing benefits       Washington – A recent American study reported that regular exercise in middle age reduces the chances of stroke in old age.     The study was conducted by researchers at the University of North Carolina, and its results were published Sunday in the Journal of the American Heart Association.  …