That gray matter, known as the cerebral cortex, is the part of the brain that processes information.
Activities ranging from golf to gardening and swimming can help preserve that gray matter, according to a preliminary study presented in Chicago Monday at the Radiological Society of North America. Those of the 875 study participants who burned the most calories had 5-percent more gray matter.
Physical activity -- about 1/2 hour to an hour each day -- appears to improve blood flow and cell connections in the brain. Brain shrinkage is suspected of playing a role in dementia and Alzheimer's.
"With the variety of 15 different activities we looked at from dancing to calisthenics to aerobics to riding and exercise cycle there was enough variety to show these can positively affect the brain so people can customize their physical activities to what they prefer and they don't have to follow a one size fits all program," Dr. Cyrus Raji, radiologist, U of California Los Angeles, said.
While the research does show a link between activity and brain health, it does not prove exercise preserves brain size. But researchers say this is exciting work.