A study looking at 1,094 participants from the Framingham Heart Study shows that people who are more physically active in middle age tend to have larger brain volumes in later life.
The study participants were an average age of 40, with no signs of dementia or heart disease. They took a treadmill fitness test and underwent MRIs. Twenty years later, they underwent another treadmill test, along with MRI brain scans.
The estimates of brain volume were calculated based on measurements of oxygen used during treadmill tests, together with blood pressure and heart rate tests. Based on these estimates, people who were more active in their 40s tended to have larger brain volumes twenty years later.
Links to articles about the study and the study itself have been posted in Health > Physical Exercise:
People who exercise at middle age might have bigger brains later on
Exercise at middle age may keep brain bigger later in life
Better Fitness In Middle Age May Stop This Organ From Shrinking