Walking may slow the cognitive decline in adults with Alzheimer's disease, according to a new study presented Monday at the annual meeting of the Radiological Society of North America.

The study, done by Cyrus Raji at the University of Pittsburgh, found that walking about eight kilometres per week helped to slow memory loss.

"We found that walking . . . protects the brain structure over 10 years in people with Alzheimer's and MCI, (mild cognitive impairment) especially in areas of the brain's key memory and learning centres," said Raji. "We also found that these people had a slower decline in memory loss over five years."

Alzheimer's is an incurable brain disease that destroys memory and cognitive skills. According to the Alzheimer's Society of Canada, there were about 480,000 Canadians with Alzheimer's and related dementia in 2008. The society estimates that number will reach 1,125,200 by 2038.

The society also estimates the economic burden of dementia in Canada doubles every decade, increasing from $15 billion in 2008 to $153 billion in 2038.

"Because a cure for Alzheimer's is not yet a reality, we hope to find ways of alleviating disease progression or symptoms in people who are already cognitively impaired," Raji said.

For the ongoing study, Raji and his colleagues analyzed the relationship between physical activity and brain structure in 426 people, including 299 healthy adults (average age 78), and 127 cognitively impaired adults (average age 81), including 83 adults with MCI and 44 adults with Alzheimer's dementia.

The study looked at how far patients walked in a week. After 10 years, all subjects underwent MRI exams to identify brain volume changes.

"Volume is a vital sign for the brain," Raji said. "When it decreases, that means brain cells are dying. But when it remains higher, brain health is being maintained."

Subjects were also given mental state exams to track cognitive decline over five years. Physical activity levels were correlated with the exam and MRI results.

Raji said the findings showed that greater amounts of physical activity were associated with greater brain volume.

"Cognitively impaired people needed to walk at least 58 city blocks, or approximately five miles (eight kilometres), per week, to maintain brain volume and slow cognitive decline. The healthy adults needed to walk at least 72 city blocks, or six miles, per week to maintain brain volume and significantly reduce their risk for cognitive decline," Raji said in a release Monday.

"Alzheimer's is a devastating illness, and unfortunately, walking is not a cure,"Raji said. "But walking can improve your brain's resistance to the disease and reduce memory loss over time."

The Alzheimer's Society of Canada, in its Rising Tide report, urges a national dementia strategy be adopted in Canada which would include recognizing the importance of informal caregivers and an increase in all areas of dementia research.