Chicago ? Exercise is known to help prevent cognitive decline and maintain the brain as people age, and now researchers think they know one reason why.

People who engaged in long-term, regular exercise had substantially more small blood vessels in their brains and more blood flow than people who performed little exercise over the years, according to a study presented Monday.

“Exercise increases the number of blood vessels in other parts of the body,” said lead researcher Feraz Rahman of Jefferson Medical College in Philadelphia. “What we didn’t know is that it also affects the brain.”

The researchers used magnetic resonance imaging and a new three-dimensional computer reconstruction to make models of small blood vessels and blood flow in the brains of 12 healthy adults ages 59 to 75. None was considered to be cognitively impaired.

The study was presented at the Radiological Society of North America’s annual meeting and is expected to be published in the next few months. It was conducted at the University of North Carolina-Chapel Hill.