After people turn 40, their brain shrinks by about 5 percent every 10 years. But new research suggests aerobic exercise could have a protective effect, slowing this age-related deterioration and keeping the mind sharp over time. To investigate the effects of exercise on the hippocampus, a brain region essential for creating and storing memories, an international team of researchers analyzed 14 previous studies, involving 737 people between ages 24 and 76. Some of the participants were healthy; others suffered from Alzheimer’s disease, depression, or schizophrenia. The researchers split the subjects into two groups—people who engaged in various fitness regimens for up to two years and those who didn’t exercise—and compared scans of their brains. They found that aerobic activity appeared to dramatically increase the size of the left region of the hippocampus. “When you exercise, you produce a chemical called brain-derived neurotrophic factor,” lead author Joseph Firth from Western Sydney University tells ScienceDaily.com. “[That] may help to prevent age-related decline by reducing the deterioration of the brain.”