Men and women with early-stage Alzheimer's disease who were more physically fit also had larger brains compared to their counterparts in less stellar shape.
The findings, though preliminary, may indicate that staying physically fit could slow the brain atrophy (shrinkage) associated with Alzheimer's disease. Or they may indicate that some common underlying process affects both brain atrophy and cardiorespiratory fitness.
"This is a valid, reliable comparison, [but] it's cross-sectional, it provides only a snapshot of fitness as it relates to brain volume," said Dr. Gary Kennedy, director of geriatric psychiatry at Montefiore Medical Center in New York City. "We can't say if increased fitness increases brain volume. Animal models show this is possible. This sets the stage for an interventional study."
The findings are published in the July 15 issue of Neurology.
In older adults without dementia, staying in good physical shape may help offset the changes in the brain, such as cognitive decline, associated with normal aging.
But experts have not yet clearly defined whether or not physical activity has an effect on those with Alzheimer's.
"We're interested in how exercise impacts the Alzheimer's disease process. There's a lot of data in normal older adults that exercising and fitness may have a beneficial effect on brain health, but there's not a lot on Alzheimer's in terms of studies to draw on to inform our recommendations for exercise and fitness," said study author Dr. Jeffrey Burns, director of the Alzheimer's and Memory Program at the University of Kansas School of Medicine in Kansas City. "We're interested in better defining that relationship."
For this study, 57 people with early-stage Alzheimer's and 64 people without dementia, all aged 60 and over, underwent standard fitness tests and MRI brain scans.
"We used an objective, gold-standard measure of fitness which hadn't been assessed in Alzheimer's patients yet, cardiorespiratory fitness, or VO2 peak, where we basically measure how much work someone is capable of doing," Burns explained.
Participants walked on a treadmill while their oxygen consumption was measured. "At their peak, how much oxygen they're consuming is a measure of how physically fit they are," Burns said.
MRI scans measured brain atrophy.
The VO2 peak was slightly lower in people with Alzheimer's compared to controls. And individuals with Alzheimer's who were less physically fit had quadruple the amount of brain shrinkage compared to normal older adults.
"The people with higher fitness levels had larger brains, and there was a strong correlation between the two," Burns explained. "We're limited because of the study design, but it could suggest that maintaining fitness may have a beneficial effect on the Alzheimer's disease process."
"We didn't find fitness to be associated clearly with cognitive performance, but that may be, because we need to study more people or the cognitive performance measures may not be sensitive enough," he added.
The study pointed to three possible explanations for the relationship: cardiorespiratory fitness affects brain atrophy related to Alzheimer's disease; the Alzheimer's disease process affects fitness; or some other, as-yet-unknown factor underlies both Alzheimer's-related brain atrophy and physical fitness.
"We're designing a study where we try to establish the cause and effect," Burns said. "Can we use exercise to enhance fitness in Alzheimer's disease and, by doing that, will it affect disease progression?"