British researchers from Bristol University say following a regular exercise programme can significantly reduce the risk of Alzheimer's disease by as much as a third.
They suspect exercise produces such a great effect because of its benefits to the vascular system as well as releasing chemicals in the brain.
They also say there is evidence that physical activity is important for psychological well-being, mood and self-esteem and helps avoid depression.
According to the Bristol team, a study they carried out which was based on 17 trials, found that physical activity was associated with a 30-40 per cent reduced risk of developing Alzheimer’s.
Health experts say only 35 per cent of men and 24 per cent of women reach the recommended 30 minutes of moderate intensity physical activity at least five times a week.
Their research was presented at a British Nutrition Foundation (BNF) conference along with other research which linked a lack of exercise to depression and dementia.
Judy Buttriss, the director general of the BNF, says given that people are living longer, the implications of such studies were "enormous".