A new study from Harvard University says walking about 5,000 steps each day can slow down problems with thinking and memory in older people.
The researchers watched 296 adults who were 50 to 90 years old.
All the people had normal thinking at the start.
For up to 14 years, the team checked their walking with small devices and tested their brain health.
People who walked 3,000 to 5,000 steps a day slowed memory loss by about three years.
People who walked 5,000 to 7,000 steps slowed it by about seven years.
Walking more than 7,500 steps did not give much extra help.
The team says 5,000 steps is a realistic goal for many older people who do little exercise now.
They suggest adding small walks to daily life, like taking the stairs or walking to the shop.