If you want to keep your brain healthy as you age, make sure you get plenty of exercise.

A new study, from the University of Illinois at Urbana-Champaign, says three areas of the brain that are adversely affected by aging stay in better shape when a person keeps their body physically fit. The study appears in the February issue of the Journal of Gerontology.

This is the first study to show anatomical differences in white and gray brain matter between older people who are physically fit and those who are less fit.

The study included 55 people over the age of 55. The researchers used high-resolution magnetic resonance imaging to assess the brains of the study participants.

The researchers focused on three areas -- the frontal, temporal and parietal cortexes. The study found distinct differences between the physically fit people and the less fit people. Those differences were especially apparent in two types of brain tissue -- white and gray matter.

The gray matter in your brain consists of thin layers of cell bodies such as neurons. Gray matter also includes support cells that are important in learning and memory. White brain matter is the myelin sheath that contains nerve fibers that transmit signals throughout the brain.

As you age, these white and gray matter tissues shrink in a pattern that closely matches declines in cognitive performance.