Some studies have linked doing brainy puzzles and physical exercise with a decreased risk of developing Alzheimer's disease, or with staving off the cognitive decline associated with the disease. But now, new research suggests otherwise.
The latest study on the topic found that staying physically and mentally fit may help healthy people ward off the normal mental decline that comes with aging, but it doesn't affect the underlying causes of Alzheimer's disease.
In people with Alzheimer's, the brain contains abnormal, fuzzy, cloudlike clusters of fragments of a protein called beta-amyloid that surround nerve cells and block their signals. This leads the person's brain function — and, in particular, memory — to deteriorate.
In the new study, researchers looked at beta-amyloid and other markers of Alzheimer's, to see if the levels of these markers in people's brains responded to physical and mental exercises.
The results indicate that exercising "may possibly be separate from any protection against the markers of Alzheimer's disease in the brain," study author Dr. Keith A. Johnson, co-director of the Massachusetts Alzheimer's Disease Research Center at Harvard Medical School, said in a statement.
Johnson and his colleagues studied 186 healthy people whose average age was 74. The participants wore pedometers for seven days to measure how active they were, and also reported their lifelong levels of physical activities such walking and gardening, and mental activities such reading and doing crossword puzzles. The participants also took tests that evaluated their memory and how fast they could think.
Brain scans of the participants showed that their levels of beta-amyloid, the size of a brain region called the hippocampus and the brain's ability to metabolize glucose were not linked with their lifelong levels of physical or mental activity. (Disruptions in glucose metabolism and a smaller hippocampus are both linked with Alzheimer's.)
Although the researchers did find a slower cognitive decline among participants who read frequently and did crossword puzzles, among other mentally stimulating activities, there was no link between mental stimulation and the actual brain's markers of Alzheimer's.
Although the study is limited by patients' memories of their past activities, the findings indicate that the underlying causes of Alzheimer's cannot be altered by human activity, Johnson said. Still, further studies are needed to follow people's activities over longer periods of time.
However, Johnson said "sustaining a lifetime of intellectual engagement may help preserve cognitive function into old age." He noted that people should not feel discouraged to exercise, as many studies indicate that mental and physical exercise have ample brain benefits.