Good heart and lung fitness can benefit older adults' brains, researchers report.

They assessed the heart/lung fitness of healthy young adults (aged 18 to 31) and older adults (aged 55 to 74), and compared their ability to learn and remember the names of strangers in photos. MRI scans recorded images of their brain activity as they learned the names.

The older adults had more difficulty with the memory test than the young adults. But older adults with high levels of heart/lung fitness did better on the test and showed more brain activity when learning new names than those of their peers with lower levels of heart/lung fitness.

The increased brain activity in those with higher levels of heart/lung fitness occurred in regions typically affected by age-related decline. The findings suggest that heart/lung fitness may also help keep the brain healthy as people get older, according to the researchers. But the study did not prove a cause-and-effect link.

"Importantly, [heart/lung fitness] is a modifiable health factor that can be improved through regular engagement in moderate to vigorous sustained physical activity such as walking, jogging, swimming or dancing," said study corresponding author Scott Hayes. He's an assistant professor of psychiatry at Boston University School of Medicine.

"Therefore, starting an exercise program, regardless of one's age, can not only contribute to the more obvious physical health factors, but may also contribute to memory performance and brain function," Hayes said in a university news release.

The researchers said high levels of fitness will not prevent brain decline, but may slow it.

The findings were published recently in the journal Cortex.