July 16, 2012 -- Being physically active -- whether it's aerobic activity like walking or resistance training to build muscles -- can keep your brain sharp and potentially reduce your risk of getting Alzheimer's disease, new studies show.
Exercise can even grow the brains of older adults, says researcher Kirk I. Erickson, PhD, assistant professor of psychology at the University of Pittsburgh.
In his recent study, older adults without Alzheimer's, aged 60 to 80, who walked moderately for 30 to 45 minutes three days a week for a year had a 2% increase in the volume of their hippocampus, a region of the brain important for memory.
He also found growth in another brain area important for memory, the prefrontal cortex.
"I would say this is pretty dramatic," he tells WebMD. "This is only after one year of exercise and moderate intensity at that."
He presented his findings at the Alzheimer's Association International Conference 2012 in Vancouver.
Another study found benefits for resistance training in adults who already have noticeable changes in thinking and memory. Until now, it has been little studied for its effect on memory and brain health.
About 5.4 million Americans have Alzheimer's disease, the Alzheimer's Association estimates.
Erickson assigned 120 older adults who had no dementia but had been inactive for the past six months to either a moderate-intensity walking group or a stretching-toning group for a year.
Before the study, he did brain imaging studies to measure the size of the hippocampus. He also looked at the size of the prefrontal cortex. "The prefrontal cortex is also involved in some memory functions, and it also tends to decay as we get older," he says.
He took blood samples and measured the concentrations of a substance called brain-derived neurotrophic factor (BDNF). "BDNF is critical in the development of new neurons," Erickson tells WebMD. "It also seems to be critical in learning and memory."
He gave the men and women a battery of tests to assess their thinking skills. He looked at such measures as their ability to switch between doing different tasks and their memory.