Physical Activity Linked to Lower Risk of Vascular Dementia But Not AD

Susan Jeffrey
December 21, 2007 — Results of a new prospective study have found an association between increasing levels of physical activity and a lower risk for vascular dementia, but not for Alzheimer's disease (AD). "Our findings show moderate physical activity such as walking and all physical activities combined lowered the risk of vascular dementia in the elderly, independent of several sociodemographic, genetic, and medical factors," first author Giovanni Ravaglia, MD, from University Hospital S. Orsola-Malpighi, in Bologna, Italy, said in a statement from the American Academy of Neurology. "It's important to note that an easy-to-perform moderate activity like walking provided the same cognitive benefits as other more demanding activities."
Unlike some previous reports, they did not find a relationship between increased activity and reduced Alzheimer's disease risk. However, the researchers note they cannot rule out that they may have missed such an association because of a lack of statistical power.
Their findings are published online December 19 in Neurology.
Walking Away from Dementia?
Observational and intervention studies have consistently shown an association between physical exercise and better cognitive performance in selected samples of older adults, although not all studies have confirmed this finding, the authors write.
Longitudinal studies of this link in the elderly are fewer and have had inconsistent results, they note. "A lower risk of all-cause dementia and AD among subjects regularly practicing low- to medium-intensity physical activities was found in some population-based studies but not in others," they write. "Moreover, only a few investigations examined the effect of physical activity on vascular dementia (VaD) risk, and none reported an association."
To look at the effect of physical activity on the risk for AD and VaD, Dr. Ravaglia and colleagues used data from the Conselice Study of Brain Aging (CSBA), a prospective, population-based cohort of 749 Italian subjects aged 65 years and older who were cognitively normal in 1999–2000 after an extensive assessment for clinically overt and preclinical dementia. Baseline physical activity was measured as energy expenditure on activities of different intensities, including walking, stair climbing, moderate activities, vigorous activities, and total physical activity.
During 2003–2004, subjects underwent a follow-up examination looking for overt dementia. Over nearly 4 years of follow-up, there were 86 incident cases of dementia, including 54 cases of AD and 27 of VaD.
The researchers found that, after adjustment for sociodemographic and genetic confounders, the risk for VaD was significantly lower for the upper vs lower tertiles for walking, moderate activity, and total physical activity, associations that persisted after vascular risk factors and overall health status were accounted for.
After similar adjustment for sociodemographic and genetic confounders, the risk for AD was not associated with measures of physical activity, they write. These results did not change after further adjustment for vascular risk factors and overall health and functional status.
"However, because of the width of the CIs for AD found in the CSBA study, it cannot be excluded that significant results for this dementia subtype may have been missed by lack of statistical power," Dr. Ravaglia and colleagues write. "Therefore, we caution the reader against concluding that this study provides definite evidence that AD is not preventable through exercise."
More research on the biologic mechanisms linking physical activity and cognition is needed, they note, but they float a variety of "not mutually exclusive" hypotheses on how cognition may benefit from physical activity. For example, physical activity may improve cerebral blood flow and lower the risk for cerebrovascular disease. Alternatively, activity may stimulate synaptic plasticity, secretion of trophic factors, neurotransmitter synthesis, and neurogenesis to increase cognitive reserve or decrease the secretion of stress hormones such as cortisol that may be toxic.
"Finally, more than from exercise itself, the beneficial effects of physical activity on cognition might result, all or in part, from the mental and social stimulation related to an active lifestyle."
The study was supported by grants from the Italian Ministry of University and Scientific Research (basic-oriented research funds). The authors report no conflicts of interest.
Neurology. Published online December 19, 2007.