The researchers said brain scans showed older adults who did not exercise had more unpredictable cerebral blood flow than those who did exercise.

"The active adults had more small blood vessels and improved cerebral blood flow," study senior author Dr. J. Keith Smith said in a statement. "These findings further point out the importance of regular exercise to healthy aging."

Using a method developed in their lab, the researchers were able to construct 3-D models of the blood vessels of 12 healthy adults -- ages 60 to 76. Six of the adults had participated in aerobic exercise for three or more hours per week over the last 10 years, and six exercised less than one hour per week.

The findings were presented by Feraz Rahman at the annual meeting of the Radiological Society of North America held in Chicago.

"Our results show that exercise may reduce age-related changes in brain vasculature and blood flow," Rahman, now a medical student at Jefferson Medical College in Philadelphia, said in a statement. "Other studies have shown that exercise prevents cognitive decline in the elderly. The blood vessel and flow differences may be one reason."