In the U.S. some five million people have Alzheimer’s disease and 10 million boomers will be at risk for memory problems over their lifetime. Worldwide, more than 100 million people may have Alzheimer’s by the year 2050. As clinicians, we have learned to recognize that jokes about “old-timer’s disease” and “Teflon brain” are often calls for help from seniors worried about their memory lapses. Living longer is obviously no fun if you cannot remember your home address or drive a car. Although we have made tremendous progress in understanding brain changes that accompany aging and dementia, no medications have proven effective for preventing Alzheimer’s to date. In recent years, however, more evidence is pointing to a non-medical way to bolster brain health as we age: exercise.
The Benefits of Exercise
Scientists are excited about the prospects of physical activity and exercise as anti-Alzheimer strategies for many reasons. Exercise training has been shown to reduce risk factors for dementia such as blood pressure, cholesterol, diabetes and depression. Studies in animal models of aging show that exercise can increase blood flow, stimulate nerve cell growth in regions associated with memory and reduce the pathologic changes characteristic of Alzheimer’s. Studies of exercise and memory in humans have been promising but not yet definitive. For example, some, but not all, observational studies of older adults time found that those who were more physically active (for example, in such activities as swimming, walking, ballroom dancing) or who exercised at least three times a week had a lower risk for dementia. Likewise some short-term clinical trials found that aerobic exercise improved certain cognitive abilities. The inconsistency across studies has hampered firm conclusions about the relevance of these findings, however. What was needed to move the field forward was a clinical trial testing whether regular exercise could produce sustained long-term improvements in older adults with memory problems.
In a study published in September 2008, Nicola Lautenschlager and colleagues at the University of Western Australia attempted to do just that. They studied 170 older people with memory complaints of whom 60 percent had objective memory deficits severe enough to be diagnosed with mild cognitive impairment, a condition thought to be a precursor for Alzheimer’s.
Over the next six months, half of the study participants were assigned to a home-based exercise program. They were encouraged to do at least three 50-minute sessions of exercise (mostly walking) each week. Those who were already doing this level of exercise at study entry (about 25 percent) were asked to up their activity level by an additional 50 minutes. The other half were assigned to receive basic health education as a control group. At the end of six months, exercisers improved modestly (scoring about 20 percent higher than controls) on an overall measure of cognitive abilities. The subgroup of people with mild cognitive impairment also improved. One year after the trial ended, the exercisers still sustained a 10 percent edge on overall cognitive score compared with controls and also had significantly less decline on a memory measure. A host of other cognitive subtests did not differ between the groups, however. This study is important because it is the first to demonstrate that exercise benefits cognition in older adults with subjective and objective memory problems over 18 months.
But this study was not a clean win and raises additional questions. The effect size was too small for an average person to be able to notice a benefit (although any effect is better than nothing in a field with no alternatives). Compliance with exercise decreases over time: Can we motivate people to sustain exercise habits over long periods? Are memory benefits seen only with aerobic exercise or can any type of physical activity help? This study did not follow people long enough to address the billion dollar question: Can regular exercise postpone the development of Alzheimer’s disease? The study by Lautenschlager and colleagues provides an important proof of principle and will help us design future trials to test these issues further. The availability of newer brain scans will also help us directly track whether exercise can affect the progression of Alzheimer brain pathology in people at risk. It has been said that “a man’s health can be measured by which he takes two at a time—pills or stairs.” As our society grows increasingly reliant on medications, lifestyle strategies such as exercise seem like, well, a no brainer.
Are you a scientist? Have you recently read a peer-reviewed paper that you want to write about? Then contact Mind Matters editor Jonah Lehrer, the science writer behind the blog The Frontal Cortex and the book Proust Was a Neuroscientist.