A new book on memory loss - 'Can't remember what I forgot' by Sue Halpern - has highlighted the importance of exercise in helping to stave off memory loss. The book surveys the scientific progress - or lack thereof - in the hunt for a cure for Alzheimer's and concludes the 'one incontrovertible means of neurogenesis' is aerobic exercise. Exercise promotes new cell growth in old brains by increasing their blood volume and in turn cell growth improves memory. Exercise also increased the amount of brain-derived neurotrophic growth factor in the brain, again stimulating cell growth. Exercise was unable to prevent the growth of amyloid plaques, one of the main hallmarks of Alzheimer's disease, but it did allow the brain to cope with them better.
You can read the New York Review of Books review of Can't Remember What I Forgot at