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Physical fitness, diet may help brain drain
10/02/2002
You can't tell all of aging's effects by looking in the mirror.
Brain shrinkage, for example, is one of the age-related changes in the
brain that researchers have recently discovered.
Now that new probes of cerebral anatomy and chemistry can catch the
brain in the act of aging, scientists can take a closer look at what's
happening in people's heads as their mental powers decline.
Others have found ways to make older brains work like younger ones when recalling information. And certain foods, dietary supplements and hormones may shield the brain from chemical processes that cause aging. Exercise seems to help, too.
Eventually, though, the brain will wear down. But by studying changes in aging brains, scientists hope to find new ways to slow the process. And by sorting out the differences between changes of normal aging and those caused by diseases such as Alzheimer's, researchers may find better ways to deal with both.
Varying rates
Some parts of the brain are hit harder by aging, and some people's brains shrink more than others'.
On average, this 3-pound organ loses 5 percent to 10 percent of its weight between the ages of 20 and 90. Volume, too, decreases. Scientists aren't sure why, but they think these changes may result from a loss of connections between nerve cells in the brain, damage to the material that insulates them or simply the death of brain cells.
In elderly people, more shrinking of a certain part of the brain has recently been linked to poorer working memory. Working memory is the kind that allows you to remember a phone number for long enough to write it down. This brain region, called the prefrontal cortex, is a section of the outer shell of the brain that sits right behind the forehead. It's one of the areas most likely to shrink as people age. Loss of working memory "is absolutely a hallmark of aging," says Jeri Janowski, a neuroscientist at Oregon Health & Science University. Dr. Janowski is a co-author of the paper that addresses that topic, published in May in the journal Cerebral Cortex.
Problems with memory in older brains may have other physical roots, too.
Some older people don't use all the parts of the brain that younger people do to recall information, reports a group of scientists led by Randy Buckner at Washington University in St. Louis.
The team looked for areas of the brain that showed increased blood flow (a sign of activation) when subjects tried to access a list of words they had memorized.
Many of the older subjects (average age 75) couldn't recruit all the areas of the brain that the younger subjects (average age 21) used. The old people also had more trouble remembering the words, the team reported in February in the journal Neuron.
When given memorization strategies, older people tended to activate the same areas of the brain as the younger people during recall and to perform better.
"The cognitive resources to handle hard tasks aren't necessarily lost," says Dr. Buckner. They're just not being accessed. "Various types of cognitive training might be able to take advantage of that."
Dr. Buckner thinks short-circuits that keep the critical areas from firing up might be caused by age-induced damage to the white matter of the brain. White matter contains a thick tangle of insulated cables that provide long-distance telephone service for the brain's neurons (nerve cells). The cables allow cells in different parts of the brain to communicate.
Physical fitness has a role in this. "There is some data coming out that shows that the healthiest individuals, the most aerobically fit individuals, show the least amount of changes in these structures," says Dr. Buckner.
Aerobic fitness seems to be good for other parts of the brain, too. Some researchers have even begun to link fitness to performance on mental tests.
One exercise psychologist recently studied the effects of cardiovascular exercise.
Charles Hillman, of the University of Illinois at Urbana-Champaign, looked at older people's ability to recognize and react to a stimulus using a brain function called executive control. This function plays a key role in the brain's ability to process and react to simultaneous stimuli – in a sense, to multitask.
With aging, executive control becomes less efficient, making it more difficult to negotiate in the world. Driving, for example, becomes harder.
Comparing the physically fit to the more sedentary, Dr. Hillman found a quicker electrical brain response among those who were fit. "You take these older, fit adults and you find that they process information at nearly the same speed as young adults," says Dr. Hillman, who presented his work at the American College of Sports Medicine last spring.
Scientists are not sure how big an effect exercise can have, or how much is necessary to see a difference in mental abilities.
"The people I've used in the past are very active, and these are runners, marathoners and what not. It would be interesting to see if that single walk after dinner is sufficient enough," says Dr. Hillman.
It's not clear how exercise helps, but one idea is that it combats the decreased efficiency of blood flow in the brain caused by aging. High blood pressure may exacerbate these blood-flow problems and over time, "could lead to the disruption of cables that allow neurons to communicate with each other," says Dr. Buckner.
Adding antioxidants
There may be other ways to keep aging neurons talking to each other. Researchers recently showed that communication between the neurons in rats' brains could be improved by supplementing their diets with foods naturally high in antioxidants. Antioxidants from food are thought to protect the brain by soaking up damaging chemicals that cells inadvertently produce during their normal activities.
A group led by Paula Bickford at the University of South Florida monitored the electrical relays in the brains of old rats, already showing signs of aging. "With a very short period of feeding, we could bring the communication between the neurons back to normal," says Dr. Bickford, whose work was published in July in The Journal of Neuroscience.
More brainpower seemed to follow the improved communication. When the old rats were fed a spinach-supplemented diet (spinach is rich in vitamin E, an antioxidant) for six weeks, they quickly learned to associate a tone with an air puff to their eyes. Older rats not fed spinach were slower to learn and often wouldn't close their eyes to avoid the air puff.
A hopeful idea
Although Dr. Bickford hopes an antioxidant-rich diet can also help humans, she's not overly optimistic. "You don't want to overinterpret these studies so that people think that if they go out and eat spinach they are going to miraculously be smart."
Many scientists, in fact, urge caution when discussing the potential of slowing or stopping brain aging and mental decline. Although there are a number of chemicals – like antioxidants and hormones – that have potential to retard brain aging, they are unlikely to be a miracle cure.
"I think that it's unlikely that you can take a human with significant cognitive decline and see a large improvement," says Dr. Bickford.
The amount of food you eat can also influence how well your brain holds up. Some evidence shows that in addition to increasing overall life span, restricting calorie intake might protect the brain and help preserve mental abilities. Intellectual activity is also emerging as an important factor in keeping the brain youthful.
Rather than prevent brain aging, substances called cognitive enhancers aim to treat the symptoms.
Several drugs in this category are approved by the Food and Drug Administration for use in Alzheimer's patients only. Other substances sold as cognitive enhancers are unproven and unregulated.
Ginkgo biloba, an extract from the ginkgo tree, is the most popular cognitive enhancer. In 1997, Americans spent $240 million on ginkgo biloba. Despite its popularity, evidence to back up its efficacy is flimsy.
"I don't think that there's any cognitive enhancer proven to have a major effect on the brain," says Dr. Jeffrey Kaye, a neurologist at Oregon Health & Science University.
Ginkgo ability
Ginkgo was shown to have some effect on the mental abilities of those suffering from Alzheimer's disease. But whether it can help those with nondiseased, or healthy, brain aging is unclear. (Though some brain changes caused by disease are similar to those seen in healthy aging, researchers are still trying to sort out the differences.)
Dr. Kaye is currently conducting a clinical trial to figure out whether ginkgo biloba can slow cognitive decline in those over 85.
So far, says Dr. Kaye, "we have not detected any adverse effects." But there have been claims in the past that ginkgo biloba causes increased bleeding complications, including gastric bleeding, because of its blood-thinning properties. These claims are not well-substantiated, he says, but there are a few reports of such problems.
People would be better off eating right, exercising, getting enough sleep and reducing stress, says Dr. Kaye, rather "than looking for a magic supplement that is going to potentially enhance their memory by less than half of a percent."
Article courtesy of The Dallas Morning News
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