In particular, walking appears to help preserve the hippocampus - a memory-making part of the brain. In older adults who do not have dementia, the hippocampus normally shrinks about 1 to 2% per year, which gradually increases the risk of cognitive impairment.  

But in a recent study, a year of dedicated moderate-intensity walking resulted in about a 2% increase in volume, which researchers say is about the equivalent to rewinding the brain-aging clock about 1 to 2 years.

In the study, older adults who were not regular exercisers were assigned to year-long exercise programs focusing on either walking or doing a combination of stretching and toning three times a week. After a year, imaging scans of the brain showed that hippocampus volume increased in the walkers but actually decreased a bit in the stretchers and toners.

When researchers reviewed nine similarly structured studies involving nearly 35,000 adults over the age of 65, study results suggested that gait speed was a big predictor of how long people would live. To reap longevity rewards and live longer than expected, people's everyday walking speed needed to be at least 2.25 miles per hour. That's a little over 3 feet every second. People with this gait speed typically outlived the slower-striding folks in the study.

In a study, women who walked at least 2 hours a week - think 30-minute walk, four times - were 30% less likely to suffer a stroke compared with nonwalkers.

Brain-Saving Steps
With the increase in brain volume, blood levels of an important memory-supporting protein called brain-derived neurotrophic factor also increased - which probably helps explain why the walkers who had bigger-than-average brains at the outset and achieved the greatest volume increase during the study intervention also made the biggest improvements on spatial memory tests.

Researchers think that aerobic exercise helps boost brain matter because it increases blood flow to the brain.  Studies have also shown that walking can help increase the brain's ability to learn, retain, and use new information.