DEMENTIA:

If you want to reduce your chances of Alzheimer's and dementia in your latter years, start exercising, and preferably up to three times a week. New research suggests that a good exercise regime is one of the best ways to stay mentally sharp throughout your life.
The exercise needn't be onerous, even if it does have to be frequent. It's enough to exercise for just 15 minutes a day, and it can include vigorous walking, hiking, aerobics, calisthenics, swimming, water aerobics, weight training, and stretching.
Researchers monitored the mental health of 1,740 participants who were 65 years or older. Over the following six years 158 people developed dementia. But those who exercised in some way at least three times a week were far less likely to develop dementia than those who exercised less often. Overall the risk was reduced by 38 per cent in those who exercised.