Research Brief: To Preserve Your Gray Matter, Take a Hike

Hard on the heels of a recent debate about the value of preventive measures for Alzheimer disease (AD) come some new data on physical activity. As reported in the October 13 Neurology online, walking spares gray matter loss in older adults. By extrapolation, this preservation should reduce the risk for cognitive impairment, according to the authors. It is unclear if this finding might change any minds on the NIH expert panel that recently pronounced available evidence insufficient to allow specific recommendations for AD prevention (see ARF related news story). However, the length of follow-up and number of subjects are strengths of the study. “Also, for the first time we’ve been able to put a number on the quantity of physical activity you should aim for,” said senior author Kirk Erickson, University of Pittsburgh, Pennsylvania. Previous work suggested that “more is better,” which is too vague when it comes to prescribing an activity, said Erickson. His findings indicate that walking six to nine miles per week prevents gray matter loss, but walking more than that brought no additional benefit.

Age-related loss of gray matter is cause for concern, especially since it correlates with cognitive impairment (see ARF related news story). Several small, cross-sectional studies of short duration suggest that exercise can help preserve gray matter (see Colcombe et al., 2003) and can protect against AD (e.g., see ARF related news story on Burns et al., 2008), but longitudinal evidence on exercise and gray matter loss has been lacking.

The Cardiovascular Health Study-Cognition Study began in 1989. At study onset, physical activity measures were taken for all 1,479 participants. Nine years later, 516 of them received a high-resolution MRI. Erickson and colleagues examined 299 of these scans using voxel-based morphometry, which measures brain volume in a point-by-point fashion throughout the brain. They correlated brain volume with exercise, splitting the study population into quartiles based on how far people walked per week.

The researchers found that those who walked at least 72 city blocks per week (about six to nine miles) had statistically larger gray matter (GM) volume in a variety of brain areas, including the precuneus and hippocampus, regions associated with AD pathology. Furthermore, greater volume in the inferior frontal gyrus, hippocampus, and supplementary motor regions halved the risk of becoming cognitively impaired. “In short, walking greater distances was associated with greater GM volume in specific regions, and greater GM volume was associated with a lower risk for experiencing cognitive impairment in later years,” write the authors.

It is unclear how the NIH expert panel would weigh this one study. Part of the problem, Erickson noted, is that it is difficult to compare exercise across studies. “There are a lot of different ways to go about measuring it,” he said. Some studies might count raking leaves or bowling as exercise, for example, while others do not. He anticipates that the availability of sophisticated measuring devices, such as pedometers and accelerometers, should help researchers better quantitate physical activity. That will be important going forward with controlled trials. “There is a lot of evidence that exercise seems to be doing something good and that it is effective at enhancing memory and cognition, but we need more randomized trials to examine this from a purely scientific perspective,” he said.—Tom Fagan

Comments

  1. I am very delighted to further understand that exercise can help preserve gray matter and thus may help prevent Alzheimer's disease in older people. This is particularly critical to populations at greatest lifetime risk for development of AD. Everywhere we turn, we hear information about the benefits of exercise. From building stronger bones and muscles to reducing the risk of heart and muscular diseases and diabetes mellitus. The effects of physical exercise on general health are certainly far ranging. In fact, a growing body of research is demonstrating that physical exercise is good for our brains. Recent research has found a link between physical exercise and the central nervous system: Exercise has shown positive effects on a wide range of brain health markers (White, 2005). In general, exercise improves the heart's ability to pump blood and increases the natural ability of blood to carry oxygen to cells throughout the body. With exercise, blood circulation to the brain is thus increased and the brain receives more oxygen and glucose, both of which are crucial to brain function. The brain is the body's most active organ, and it consumes the most energy (i.e., between 20 and 30 percent of the body's total) (Bloor, 2005). Exercise also appears to have profound effects on specific molecular levels involved in the regulation of neuroplasticity. Hence, there is the added benefit of keeping your brain healthy, that is, to lead to an increase in cognition and memory.

    Despite such declines in cognitive and motor processes during the course of aging in people with HD, recent findings suggest that physical exercise can minimize some, but not all, kinds of cognitive decline. A recent study showed that older adults who exercised throughout life had less brain tissue loss and performed significantly better on cognitive tests than adults who exercised infrequently (Stanford’s Huntington's Disease Project, 2006). It is important to note that this research and many other recent studies on exercise and cognitive function only show correlation, but not necessarily prove causation. I agree very much that longitudinal evidence on exercise and gray matter is critical to understanding the effect of exercise on gray matter and white matter in the brain, particularly in the frontal lobe, temporal lobe, and parietal lobe. In addition, stress leads to the release of various neurochemicals and hormones (Leserman et al., 2000). Prolonged exposure to stress hormones is detrimental to the health and survival of nerve cells, and thus cognitive function will be affected. Therefore, exercise, stress, and other physical or environmental factors can be some important factors to be researched for improvement of cognitive and memory functions, as well as for prevention of AD.

    References: See also Stanford’s Huntington Disease Project (2006). Advanced Stages of Huntington's Disease Caregivers Handbook: Exercise and Fitness. See website.

    References:

    Bloor CM. Angiogenesis during exercise and training. Angiogenesis. 2005;8(3):263-71. PubMed.

    Leserman J, Petitto JM, Golden RN, Gaynes BN, Gu H, Perkins DO, Silva SG, Folds JD, Evans DL. Impact of stressful life events, depression, social support, coping, and cortisol on progression to AIDS. Am J Psychiatry. 2000 Aug;157(8):1221-8. PubMed.

    Petrovitch H, White L. Exercise and cognitive function. Lancet Neurol. 2005 Nov;4(11):690-1. PubMed.

    View all comments by Wai-Tong Chien

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References

News Citations

  1. NIH Calls for More (and Different) Research on Preventive Measures
  2. I Told You I Was Sick: Brain Atrophy Associated with Subclinical Memory Loss
  3. Is Ventricle Size a Good Measure of AD?

Paper Citations

  1. Colcombe SJ, Erickson KI, Raz N, Webb AG, Cohen NJ, McAuley E, Kramer AF. Aerobic fitness reduces brain tissue loss in aging humans. J Gerontol A Biol Sci Med Sci. 2003 Feb;58(2):176-80. PubMed.
  2. 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. PubMed.

Further Reading

Primary Papers

  1. Erickson KI, Raji CA, Lopez OL, Becker JT, Rosano C, Newman AB, Gach HM, Thompson PM, Ho AJ, Kuller LH. Physical activity predicts gray matter volume in late adulthood: the Cardiovascular Health Study. Neurology. 2010 Oct 19;75(16):1415-22. PubMed.

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