(USA TODAY) -- Cardiac index -- the measure of how well the heart is pumping blood to the brain and the rest of the body -- may be an indicator of a person's risk for developing dementia in the future.

A study in this week's Circulation suggests cardiac index is linked to brain size, even in people without heart disease, a known risk factor for dementia.

"The primary finding is that cardiac index is associated with brain volume. Participants with low cardiac index and low normal values had smaller brains, equivalent to about two years of brain aging compared to those with high cardiac index," says study author Angela Jefferson, associate professor of neurology at the Alzheimer's Disease Center at Boston University School of Medicine.

The study evaluated data from 1,504 participants in the Framingham Offspring Cohort, an arm of the larger Framingham Heart Study. Information was collected from neuropsychological tests, brain and cardiac MRI and lab reports.

Doctors have long known that the heart and brain are intertwined and that heart disease is a risk factor for dementia and Alzheimer's, says Richard Lipton, an attending neurologist at Montefiore Medical Center and professor of neurology at the Einstein College of Medicine in New York. But he says these results take into account non-heart patients, too.

"These are not people with heart disease, so that's what makes it interesting," Lipton says.

Will the results translate into public-health recommendations? "I'm not entirely sure yet. But I think sometimes we give drugs that reduce high blood pressure, that (also) reduce cardiac index, and maybe people will begin to think twice about that," he says.

William Borden, assistant professor of medicine in public health at the Perelman Heart Institute at New York-Presbyterian Hospital/Weill Cornell Medical Center, says the study "helps give us a better understanding of what potentially could lead to dementia in older people, and the role that cardiac dysfunction, or weak hearts, play in brain function or dysfunction."

"But we don't want to overstate the article," he says. "It is important, certainly suggestive, but it is observational data and can't prove anything just yet."

Author Jefferson, who says she plans to continue studying the relationship of cardiac index to cognitive health, concurs: "It's premature to say you can take this medication or engage in this particular activity to improve your cardiac output to protect brain health."

But, she says, it's still fair to encourage people to engage in healthy living choices: "Eat well, exercise regularly, and take medicines prescribed by your doctor if you have cardiovascular risk factors."

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