"A notable example is The Nun Study that suggests that positive changes in lifestyle might help to maintain your cognitive abilities. The Nun Study is a longitudinal study started in 1986. A group of nuns took a battery of cognitive tests on a yearly basis. They also donated their brains to science.
The Nun Study confirms the importance of being physically active as you age. Physical activity, like walking four times a week, improves blood flow to all of the body, including the brain. Being physically active has been shown to increase the blood flowing to your hippocampus, the area of the brain that is responsible for memory."