When the people with heart disease or those taking beta-blockers were excluded, the less fit people had reductions of brain volume equal to one year of accelerated brain aging.

Spartano added the results suggest “low fitness may be particularly harmful to the brain in people with heart disease.’’

The study, part of a large body of research devoted to physical fitness and brain health, shows an association between fitness and brain health. It does not prove that poor physical fitness causes a loss of brain volume.

“From other studies, we know that exercise training programs that improve fitness may increase blood flow and oxygen delivery to the brain over the short term,” Spartano said. “Over the course of a lifetime, improved blood flow may have an impact on brain aging and prevent cognitive decline in older age.” —Janice Lloyd