15 October 2010. 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.
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. Neurology 2010 October 13. Abstract