Physical activity is known to prevent a number of different health problems including cardiovascular disease, high blood-pressure, type 2 diabetes and certain cancers. However, the links between physical exercise and neurodegenerative diseases - dementia, Alzheimer's and Parkinson's - are less well-established. Researchers from University College London reviewed 16 long-term studies into the links between exercise and neurodegenerative diseases. They found that, compared to people who did least exercise the people who did the most exercise had only seven-tenths the risk of developing dementia, just over half the risk of developing Alzheimer's and four-fifths the risk of Parkinson's.
Hamer, M. and Chida, Y. - Physical activity and risk of neurodegenerative disease: a systematic review of prospective evidence Psychological Medicine January 2009, 39(1), 3-11