Exercise may slow Alzheimers

To keep the brain sharp, hone the body
Studies show that exercise improves all sorts of brain functions

By Shari Roan

Monday, February 06, 2006
A faster mile, bigger biceps, more stamina — all are proof that exercise hones the body. Less tangible, but no less important, is the effect on the mind.

During the past decade, neuroscientists have been churning out an abundance of data pointing to changes in the brain following physical activity. Some researchers have even suggested that the type of exercise matters — as does the age at which it begins.

"I would absolutely recommend people exercise for the mental benefits — especially the elderly," says Henriette van Praag, a staff scientist at the Salk Institute for Biological Studies in San Diego. "People don't care about whether they're a size 4 or a size 6 as they get older. But they do care where their car keys are and whether they'll have the ability to play their card games and enjoy life."

Movement appears to enhance memory, learning, attention, decision-making and multitasking, among other mental functions. It also might slow or even reverse age-related decline.

The proof comes in two forms. The first is research showing that people who exercise score better on mental tests than those who don't. Most of this research has been on older people. The second is research showing that exercise prompts structural changes in the brains of mice, spurring the growth of new nerve cells and connections between those cells.

While admittedly a far cry from human studies, the finding that new neurons can be formed later in life — called neurogenesis — is a revelation. Scientists had long assumed that we have at birth all the nerve cells we will ever have, losing them as we age.

"Neurogenesis is probably a very important contributor to the effects of exercise on learning and memory," van Praag says.

A study published in September in the Journal of Neuroscience by van Praag and the Salk researchers showed that the new neurons in older mice who began exercising were twice those of young, sedentary mice. The older, exercising mice were also better able to learn new tasks.

Exercise seems to enhance brain performance in three basic ways. One, it increases the flow of oxygen to the brain and might help build tiny blood vessels that pave the way for the growth of new cells.

Two, it boosts substances called growth factors, including one called brain-derived neurotrophic factor that is critical to the survival of new nerve cells.

Finally, physical activity increases chemicals in the brain called neurotransmitters, such as dopamine, serotonin and norepinephrine, which play roles in cognition.

"The way I think about it is that fitness changes the building blocks — the structure and function — that support numerous cognitive abilities," says Dr. Arthur Kramer, director of the Biomedical Imaging Center at the University of Illinois.

Exercise might even help stall the progression of dementia. In a study published recently in the Journal of Neuroscience, Carl Cotman and his colleagues took mice that were predisposed to develop Alzheimer's disease and gave them running wheels for exercise. After several months of exercise, the mice showed improved cognitive behaviors and less amyloid-beta plaque, a substance that accumulates in the brains of Alzheimer's patients.

"What we found is that levels of the amyloid in these exercising mice went down," says Cotman, director of the Institute for Brain Aging and Dementia at the University of California, Irvine. "Instead of a drug, it was a natural behavior that translated to a reduction of Alzheimer's-like pathology developing in the brain."

The animal studies are important because they suggest reasons why humans also demonstrate enhanced mental performance after starting an exercise program.

In 2003, Kramer compiled 18 studies on exercise and cognition and determined that there was a consistent, reliable effect. Last year, using brain scans called functional MRI, his group showed in two experiments that increases in cardiovascular fitness in humans increased the level of activity in the part of the brain associated with successful task completion.

Indeed, exercise aids regions of the brains that are most involved in age-related cognitive decline, such as executive function.

"This involves short-term working memory, multitasking. These kinds of abilities get the biggest boost," Kramer says.

In contrast, practicing a specific mental exercise, such as a memory exercise, will help your memory but won't lead to improvements on other mental tasks, such as balancing your checkbook.

Fitness seems to confer a wide range of benefits on the brain's functions. Kramer says it makes the brain more adaptive, efficient and "plastic," meaning the brain's ability to reorganize neural pathways based on new experiences.

It seems likely, scientists say, that the younger you are when you begin working out, the better.

"You can still benefit if you're older, but you'll get the maximum benefit if you're younger," Cotman says.

Research also suggests that women might have more to gain than men. Kramer's work shows that women taking postmenopausal hormone therapy benefited more from exercise than those who didn't take hormones.

Both exercise and estrogen increase brain-derived neurotrophic factor.

While weight-lifting and static exercising might be good for the brain, aerobic exercise is most likely of greater value, researchers say, possibly because it increases blood flow and oxygen to the brain. Even moderate exercise in an elderly person can improve memory and attention by 15 percent, Kramer says.

What may be most effective, experts say, are physical activities that blend exercise with a mental challenge and a social component. Frequent socialization and challenging mental tasks, such as learning a new skill, help keep the brain sharper in older age, studies have shown.

Consider walking daily with a group of friends to blend the workout with socialization, says Kramer. Or take a fitness class that prompts you to learn something new, suggests Cotman. Dance classes, for instance, combine exercise with social interaction and a mental challenge.

"We don't have to wait for a wonder drug," says Kramer. "We know there are several things that are neuro-protective: diet, intellectual stimulation and exercise. There is enough evidence to act on this."