Burns JM, Cronk BB, Anderson HS, Donnelly JE, Thomas GP, Harsha A, Brooks WM, Swerdlow RH.
Cardiorespiratory fitness and brain atrophy in early Alzheimer disease.
Neurology. 2008 Jul 15;71(3):210-6.
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This study by Burns and colleagues adds optimistically to the growing body of evidence supporting that aerobic-based physical activities, which improve cardiorespiratory fitness, are beneficial for cognitive function. There are certainly numerous possible reasons why exercise training improves cognitive function.
The results showed that participants who were more physically fit had less brain shrinkage than less-fit participants. However, they did not do significantly better on tests of mental performance. Although the authors were surprised by the small effect of exercise on cognitive performance, this should not be taken as unusual. There are several reasons why there was no significant effect between fitness and cognitive performance. For example: 1) the tests used were not sensitive enough to capture the subtle changes of exercise on cognitive function; 2) the study results were based on participants who were evaluated only once rather than repeatedly over time; and 3) the study sample was too small to show a statistically significant effect.
Even though the study presents several limitations, these results are of clinical and public health relevance since the brain shrinks with normal aging, and that rate is doubled in people with Alzheimer's. A recent review by the Cochrane Library concluded that the same aerobic exercise that is good for your heart may also have a positive effect on cognitive function—specifically, motor function, auditory attention, and memory—in healthy older adults (Angevaren et al., 2008).
Hosts of mechanisms are thought to be responsible for this activity-induced cognitive change. Animal data suggest that running can lead to an increase in new brain cells in the hippocampus, an area that plays a large role in learning and memory. Also, "cardiorespiratory trained" transgenic mice that model Alzheimer's showed decreased amyloid protein buildup in the rodents' brain (Adlard, 2005). Although researchers cannot count brain cells in studies of live humans, a study by Colcombe and colleagues (2003) showed that aerobically fit adults had reduced white and grey matter tissue loss as compared to a match sedentary group. Many important neurochemicals are influenced by exercise, including neurotransmitters and growth factors, which are being investigated for their role in cognition, and brain function. Even runner's high, that elusive euphoria that some people experience after prolonged or intensive running, is becoming clearer—literally. A study done in Germany (Boecker et al., 2008) used PET scans to look at the brains of 10 athletes following a two-hour run. The scans confirmed that during the run, endorphins were released in certain parts of the brain known to be involved with the processing of information and emotions.
The study by Burns and colleagues adds to the literature and stresses the need to further these results into the design of rigorous randomized trials to explore whether exercise and physical fitness can slow the progression of Alzheimer’s. In addition, we should start to investigate different exercise training paradigms, specifically the dose-response association between exercise and cognition since the question that needs to be answered is, How much exercise is needed to get these wonderful benefits?
Though experts do not arrive at a consensus about the right exercise protocol, recommendations, and guidelines for exercise training practices for brain health, considering overall health, any physical activity is better than nothing. When I reviewed several clinical trials dedicated to test the effects of exercise on older adults with cognitive impairments (Heyn et al., 2004), the majority of the protocols included 30 to 60 minutes of exercise sessions performed three to five times per week. The exercise protocols were based on performing movements requiring a large range of motions that use large muscle groups (such as walking, running, and stationary bicycle). Some studies support that some mental health benefits can be observed after 20 minutes of physical activity, though the more exercise and higher intensity, the better the effects. This means that following the Center of Disease Control/American College of Sports Medicine recommendations of 30 minutes of aerobic activity per day will have a positive effect on your brain as well as your heart.
Adlard PA, Perreau VM, Pop V, Cotman CW.
Voluntary exercise decreases amyloid load in a transgenic model of Alzheimer's disease.
J Neurosci. 2005 Apr 27;25(17):4217-21.
Boecker H, Sprenger T, Spilker ME, Henriksen G, Koppenhoefer M, Wagner KJ, Valet M, Berthele A, Tolle TR.
The runner's high: opioidergic mechanisms in the human brain.
Cereb Cortex. 2008 Nov;18(11):2523-31.
Heyn P, Abreu BC, Ottenbacher KJ.
The effects of exercise training on elderly persons with cognitive impairment and dementia: a meta-analysis.
Arch Phys Med Rehabil. 2004 Oct;85(10):1694-704.
Angevaren M, Aufdemkampe G, Verhaar HJ, Aleman A, Vanhees L.
Physical activity and enhanced fitness to improve cognitive function in older people without known cognitive impairment.
Cochrane Database Syst Rev. 2008;(3):CD005381.