Even modest amounts of daily exercise can slow the progression of Alzheimer's disease in older adults who are at risk of developing the disease, researchers say.
People are often recommended to walk 10,000 steps a day as part of a healthy routine, but scientists have found that 3,000 steps or more appears to delay the brain changes and cognitive decline experienced by Alzheimer's patients.
The results of the 14-year study showed that cognitive decline was delayed by an average of three years in people who walked 3,000 to 5,000 steps per day, and by seven years in those who walked 5,000 to 7,000 steps per day.
“We encourage older adults who are at risk for Alzheimer's disease to consider making small changes to their activity levels to develop sustainable habits that protect or benefit their brain and cognitive health,” said Dr. Wai-Ying Yau, first author of the study at Mass General Brigham Hospital in Boston.
An estimated 50 million people worldwide suffer from dementia, with Alzheimer's disease being the most common cause. More than 500,000 people in the UK have Alzheimer's disease. This condition is associated with the accumulation of two toxic forms of proteins in the brain, namely amyloid beta plaques and tau tangles.
Yau and her colleagues analyzed data from 296 people aged 50 to 90 who did not have cognitive impairment at the start of the study. Data included annual cognitive assessments, step counts measured by pedometers, and PET imaging to determine levels of amyloid and tau in the volunteers' brains.
People with little amyloid in their brains at the start of the study experienced very little cognitive decline or tau accumulation over the course of the study. The risk of Alzheimer's disease was higher in people with elevated baseline amyloid levels, and among them, higher step counts were associated with slower rates of cognitive decline and delayed tau protein accumulation. In people with a sedentary lifestyle, tau accumulation and cognitive decline occurred significantly faster, the researchers found. report in the journal Nature Medicine.
Although scientists can't rule out reverse causation, where early brain changes in Alzheimer's disease cause people to walk less as they get older, the evidence suggests that physical activity has a protective effect. “We need randomized clinical trials to prove cause and effect, but it's very encouraging that physical activity can help change someone's trajectory,” Yau said. “If they have amyloid, they may have a slower rate of decline if they are more physically active.”
It's unclear how exercise might help, but physical activity improves blood flow, reduces inflammation, and increases levels of certain hormones and growth factors, all of which may play a role. “In terms of potential mechanisms, that's the million-dollar question that we want to look at in future studies,” Yau said.
Dr Julia Dudley, from Alzheimer's Research UK, said: “The results show that even a modest amount of daily walking, around 5,000 steps, is associated with a slower build-up of tau protein in the brain, one of the key factors in Alzheimer's disease. This gives us a clearer picture of how daily activity can support brain health and influence the underlying causes of Alzheimer's disease.”
“More research, including clinical trials, is needed to see the direct impact of physical activity on preventing and slowing the progression of dementia, as well as the causes of underlying diseases. But studies like this confirm that simple changes to our lifestyle can help keep our brains healthy for longer.”
