"Of all the lifestyle changes that have been studied, taking regular physical exercise appears to be one of the best things that you can do to reduce your risk of getting dementia.
Prospective studies follow the health and behaviour of a group of people over time. Several prospective studies have looked at middle-aged people and the effects of physical exercise on their thinking and memory in later life. Combining the results of 11 studies shows that regular exercise can significantly reduce the risk of developing dementia by about 30 per cent. For Alzheimer's disease specifically, the risk was reduced by 45 per cent."
https://www.alzheimers.org.uk/about-...sical-exercise