Looking for a reason to be more active? Start by considering your brain.

A study out today shows people who burn off the most energy have healthier, younger brains compared with adults who do less.

Lead author Cyrus Raji of UCLA says researchers set out to determine how physical activity is associated with gray matter during aging. Gray matter, also called the cerebral cortex, gets the credit for processing much of the information we use. It is made up of neurons and nerve fibers, and its shrinkage is a possible cause of or contributor to dementia and Alzheimer's disease, a fatal degenerative illness that affects 5.2 million U.S. adults. The number of diagnoses is expected to triple by 2050.

In the study of 876 adults (ages from 69-95), those who burned the most calories had 5% more gray matter. The findings were presented at the annual meeting of the Radiological Society of North America in Chicago. The researchers used MRIs and 3-D pictures of the brain to measure volume.

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