The best doctors can do for people who are worried about developing dementia as they age is to tell them to keep their minds and bodies active.

“I think a lot of this is common sense that clinicians and researchers have come up with, but there’s some epidemiological data out there that the folks who exercise tend to be healthier later on and tend to live longer,” Dr. Michael Wasserman, a member of the board of the Health in Aging Foundation, told Healthline.

New research provides a stronger rationale for the advice that to strengthen your heart is to improve your mind as you age.

The study, published today in the online issue of the journal Neurology, suggests that exercising in middle age has measurable influence on how quickly the brain ages.

Using data from the large, long-term Framingham Heart Study, researchers, led by Nicole Spartano, Ph.D., at Boston University School of Medicine, concluded that the brains of middle-aged couch potatoes literally withered away faster than those of their more active peers.

How well participants performed on a treadmill test was directly associated to their brain volume 20 years later, the researchers found.

“We found a direct correlation in our study between poor fitness and brain volume decades later, which indicates accelerated brain aging,” Spartano said in a statement.

Read More: End-of-Life Care for Dementia More Expensive Than Cancer of Heart Disease »

Long-Term Study Provides Answers

This kind of long-term benefit of exercise is something that only a study like the Framingham Heart Study could provide, Wasserman said.

Spartano and her colleagues looked at how long the participants could remain on a treadmill as the speed and incline increased and before their heart rates reached 85 percent of their estimated maximum or they were simply exhausted. Participants did the treadmill test twice about a decade apart.

The results showed that people whose blood pressure and heart rate increased more during exercise also were more likely to have smaller brain volumes two decades later.

“A person’s fitness level is really a marker for how efficient the body is at performing exercise. So if you can perform exercise without much of an increase in heart rate or blood pressure, than you are probably in very good shape,” Spartano explained.

Read More: New Antibody May Treat Brain Injury and Prevent Alzheimer’s Disease »

Test Exposes Brain Health Risks

The researchers concluded that the exercise stress test uncovered poor vascular function, which is a risk factor for brain health. That suggests that uncontrolled high blood pressure is a risk factor for dementia.

Because exercise counteracts high blood pressure, it may be especially important for those with the condition to be active.

The Framingham study didn’t have any way to measure the 1,500 participants’ cognitive performance directly, but MRI scans revealed the size of their brains. Atrophy of the brain has been linked to diminished mental sharpness.

“This research is still somewhat new,” Spartano told Healthline. “But we do know that our brains shrink as we age, and this atrophy is related to cognitive decline and increased risk for dementia.”

There are still a lot of questions about how brain diseases such as Alzheimer’s develop. While this study doesn’t answer them, it does provide evidence to support doctors’ advice for patients to get active. 

“We do know that as people get older their brains can get smaller, but they don’t all get Alzheimer’s,” Wasserman said. “But even if we don’t have the proof that maintaining brain volume through exercise is going to make you have less cognitive decline, the reality is it can’t be bad.

There’s different reasons to exercise at different ages and this could be a very powerful piece of information to encourage people in middle age.”

Read More: PTSD Linked to Faster Aging, Earlier Death »