I would take this as an indicator that simple, ongoing maintenance of fitness and avoidance of a sedentary lifestyle pays off: "Simple tests such as walking speed and hand grip strength may help doctors determine how likely it is a middle-aged person will develop dementia or stroke. ... More than 2,400 men and women with an average age of 62 underwent tests for walking speed, hand grip strength and cognitive function. Brain scans were also performed. During the follow-up period of up to 11 years, 34 people developed dementia and 70 people had a stroke. The study found people with a slower walking speed in middle age were one-and-a-half times more likely to develop dementia compared to people with faster walking speed. Stronger hand grip strength was associated with a 42 percent lower risk of stroke or transient ischemic attack (TIA) in people over age 65 compared to those with weaker hand grip strength. This was not the case, however, for people in the study under age 65. ... Researchers also found that slower walking speed was associated with lower total cerebral brain volume and poorer performance on memory, language and decision-making tests. Stronger hand grip strength was associated with larger total cerebral brain volume as well as better performance on cognitive tests asking people to identify similarities among objects." We might theorize that this is related to exercise and blood flow in the brain, and related effects on the heath of blood vessels in the brain.