Nov. 29, 2010 (Chicago) -- Walking a little over three-fourths of a mile a day may reduce the risk of Alzheimer's disease, researchers report.
Among people who already have mild cognitive impairment (MCI), walking a similar amount may slow the brain degeneration and memory loss associated with the condition, says Cyrus Raji, PhD, a radiologist at the University of Pittsburgh.
"In cognitively normal adults, walking 6 miles a week instead of being sedentary was associated with a 50% reduction in Alzheimer's risk over 13 years," he tells WebMD.
"In people with MCI, walking just 5 miles a week reduced brain atrophy and cognitive decline -- by more than 50%," Raji says.
Any type of exercise that's equivalent to walking 5 or 6 miles a week will probably offer the same brain protection, says Robert Zimmerman, MD, a neuroradiologist at New York-Presbyterian Hospital in New York City.
Zimmerman moderated a news briefing to discuss the findings at the annual meeting of the Radiological Society of North America.
Between 2.4 million and 5.1 million American have Alzheimer's disease, according to the National Institute on Aging. Alzheimer’s is an irreversible, progressive brain disease that slowly destroys memory and cognitive skills.
People with MCI have greater memory loss than would be expected with normal aging. Research has shown that people with mild cognitive impairment are at increased risk of developing Alzheimer's disease within a few years. But not everyone who gets a diagnosis of mild cognitive impairment goes on to develop Alzheimer's.
For the ongoing study, Raji and colleagues analyzed the relationship between walking and brain structure in 426 people: 299 cognitively healthy adults, 83 people with MCI, and 44 people with Alzheimer's dementia.
When they entered the study in 1989-1990, participants were asked how many city blocks they walked in an average week, whether for exercise, chores, or any other reason. Follow-up questionnaires every three years showed that the number of blocks walked remained steady over time, Raji says.
All participants also underwent MRI exams in 1992-1994 and 1998-1999, so researchers could measure changes in brain volume.
"Brain volume is a good, reliable way" of studying brain health, Zimmerman tells WebMD. As brain cells die, brain volume drops.
In addition, participants were given the Mini-Mental State Exam (MMSE), a brief test of cognitive skills, including attention span and memory, at various times throughout the study, with the final one five years after the second MRI scan. The MMSE is used to help doctors make a diagnosis of MCI or Alzheimer's dementia.
Walking Associated With Slower Mental Decline
As shown by MRI, brain volume was preserved in healthy adults who walked at least 72 city blocks, or 6 miles, per week.
Cognitive exam and MMSE scores showed walking six miles a week was associated with a 50% decline in Alzheimer's risk over 13 years, Raji says.
Walking more than 72 blocks a week offered no additional benefit, he says.
Cognitively impaired people needed to walk at least 58 city blocks, or approximately 5 miles, per week to maintain brain volume and slow cognitive decline.
Over 10 years, scores on the 30-point MMSE dropped by an average of five points in cognitively impaired patients who were sedentary, compared with one point in those who walked 5 miles per week.
"Going down five points is a lot," Raji says. It's the difference between being cognitively normal and cognitively impaired, he says.
The association between walking and MRI and MMSE results persisted even after the analysis was adjusted to take into account other risk factors for dementia including age, gender, and high blood pressure.