This study found that people who exercised three times a week or more had a reduced rate of dementia. Findings suggest that exercise does not prevent dementia but is associated with a delayed onset of Alzheimer's disease. This might be because the area of the brain most susceptible to ischaemic damage, the hippocampus, which is also one of the earliest areas of the brain to be affected by Alzheimer's disease, shows less tissue loss in older people with higher levels of physical activity. Increasing the level of physical activity through habitual exercise has also been shown to benefit people with established Alzheimer's disease.