Exercise: Prescription for multiple sclerosis?
MS is an autoimmune disease that causes the body's own defenses to attack the nervous system, resulting in weakened muscles, fatigue, spastic muscle contractions and disability. Because MS patients are sensitive to warmth, they are often warned against exercise, but now we hear that in many studies, exercise reduces the symptoms of MS and may actually slow the damage.
In 2004 (see #1 in the bibliography), Lesley White, an associate professor of kinesiology at the University of Georgia, analyzed existing studies and reported that exercises tailored to MS patients often reduced fatigue and improved mood, while increasing strength, flexibility and walking speed.
This year (see #2 in the bibliography), White and a colleague suggested that two chemicals involved in forming and protecting nerve cells could explain these benefits:
Brain-derived neurotrophic factor (BDNF): Various animal studies have shown that exercise raises BDNF levels in the brain and in the muscles, where MS attacks the neurons that control movement.
Insulin-like growth factor-1 (IGF-1): Animal experiments have shown that exercise increases the level of IGF-1, and that blocking IGF-1 eliminates the neural benefits of exercise. Intriguingly, IGF-1 is also involved in the development of myelin, the insulating sheath on neurons that is a particular target of destruction in MS.
Exercise may be most effective soon after an MS diagnosis, before the neurons face extensive damage, White wrote. "Based on a growing body of evidence, we propose that there is a promising link between exercise, initiated with appropriate timing, and promotion of brain health in MS and other diseases."
Exercise and the aging brain
Aging may make us wiser, but it may also muddy memory, language skills, and other intellectual abilities - which psychologists lump together, grab-bag style, as "cognition." Can exercise slow or reverse the cognitive declines of aging? The question can't be answered by simply comparing runners to couch potatoes: Such a comparison could just show that smart people decide to run, and less-smart people decide to potat-ate -- if we may coin a verb...
Instead, scientists have approached the question by randomly assigning inactive people to different activities and then giving them cognitive tests. In 2003, to distill a clear message about the effects of exercise in older people, Arthur Kramer, a professor of neuroscience and psychology at the University of Illinois at Urbana-Champaign, combed through 18 existing studies. In each study, adults aged 55 or older were randomly assigned to a program of aerobics -- running, walking, biking or swimming, or to a non-aerobic program of stretching and strengthening. Then the subjects took various cognitive tests, measuring, for example, their ability to remember or do mental math (see #3 in the bibliography).
Animal research shows unquestionable benefits from aerobic exercise, Kramer says. "There are more studies almost every month," showing that rodents learn and remember more, for example, when they get to use a running wheel.
Although the results of human trials did vary, Kramer and colleague Stanley Colcombe wrote that their analysis showed in "unequivocal" terms that aerobic exercise improves cognition in older people. Translated into years, Kramer says the question becomes, "How far we can turn back the clock? Across the studies, we get two or three years."
Anaerobic exercise, in contrast, was rather ineffective in their analysis, and we must mention that at present, no drugs on the legal market produce substantial cognitive benefits in older adults (although two drugs are on the market to slow dementia in Alzheimer's disease).
Furthermore, the broad mental benefits of exercise compare well with the computer-based training packages that aim to improve the language or memory of older people, Kramer says. In lab studies, he points out, these programs offer specific benefits. "If you are training to remember information, like a shopping list, you will not get a benefit on decision making or linguistic processing." With fitness, he adds, "there was a broad effect across the board."
Kramer's analysis found that while aerobic exercise benefits specific cognitive tasks, like memory or reaction speed, the biggest boost came in "executive controls," which deals with matters like scheduling, handling ambiguity, working memory and multitasking. "That result is quite interesting," Kramer says. "I think of this as training cognition without cognitive training. People are selling [computer-based training] products for older people that have very specific effects, but maybe taking a walk would be a good idea."
Animal studies suggest the next direction for studies of cognition and exercise, Kramer says. It's been known for about a decade that exercise causes neurons to grow in critical brain regions. More recently, scientists have found that rodents get a similar benefit from living in groups rather than alone -- and that this is compounded if the rodents also get to "run to nowhere" on an exercise wheel.
So instead of comparing exercise to sloth, Kramer says, it makes more sense to look at huffing and puffing in combination with other factors that influence mental capacity, including social interaction, genetics and diet. These studies will be more complicated, Kramer admits, but the need is rising: A wave of cognitive decline faces the aging baby boomers, and it would be sweet to find a cheap, effective way to slow the menacing mental mushiness.
Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive