AARP: Here’s yet another reason to follow a smart diet and get plenty of exercise: Keeping your heart healthy just might slow down the aging of your brain.

A study released Monday found that people whose hearts pumped less blood had smaller brains—a symptom of aging—than those with the strongest blood flow. This was true even in people with no obvious signs of heart disease.

As the brain ages, it begins to shrink and lose some volume. More severe brain shrinkage occurs in those with dementia, including Alzheimer’s.

The results, published in Circulation, a journal of the American Heart Association, came from a survey of 1,504 people ages 34 to 84—54 percent of them women—in the decades-long Framingham Heart Study, a multi-generational research project.

Angela L. Jefferson, the study’s lead author and an associate professor of neurology at Boston University School of Medicine, led a team that recorded each study participant’s cardiac index, a measure of heart output. The team then used MRIs (magnetic resonance imaging) to measure each person’s brain volume.

In the study group, 30 percent met the criteria for low cardiac index, and their brain volume on average was significantly lower than people whose cardiac index was the healthiest.

“Lower cardiac output means there is less blood leaving the heart and circulating through the body, including the brain,” Jefferson says. “With less blood flow to the brain, the brain may be compromised.”

Because brain volume slowly declines with normal aging, Jefferson and her colleagues could estimate that the brains of people with poor cardiac output were more aged—by about two years—than those with the healthiest blood-pumping capacity.

Surprisingly, people in the middle group—who had low but still normal levels of blood pumping from the heart—also showed almost two years more brain aging than those with the healthiest cardiac index. “That’s a little concerning,” says Jefferson.

While abnormal brain shrinkage is associated with mild cognitive impairment and dementia, Jefferson says, more studies are needed to determine “whether or not cardiac output is a risk factor for dementia and whether or not this is something we should be modifying or assessing.”

That caution is echoed by William Borden, M.D., a cardiologist with the Perelman Heart Institute at the Weill Cornell Medical Center in New York, who pointed out that cardiac output is only one measure of heart fitness.

“The take-away from this is there’s a suggestion that poor heart function can potentially lead to poor brain function,” Borden says. “It gives more motivation to patients to pay attention to their diet and exercise and work with their physicians to control the risk for cardiovascular disease.”

Michael Haederle is a freelance writer whose work has appeared in People, the New York Times and the Los Angeles Times.