Alzheimer’s, a neurodegenerative disorder commonly associated with memory loss and confusion, is the fifth leading cause of death among United States citizens over the age of 65 years . Currently, there are no scientifically-validated treatments to prevent or delay the onset of Alzheimer’s, although it is thought that lifelong exercise may help prevent and/or lessen symptoms of this disease. Here, we review the evidence backing this claim.
In animal models, exercise is associated with less β-amyloid plaque accumulation in the brain . These plaques are found in brains of Alzheimer’s patients and are thought to be a potential causative agent , although this is not conclusive. Further, exercise increases blood flow to the brain, which is related to growth and development of nervous tissue ; this is expected to be related to improved cognition.
Several prospective cohort studies have compared groups of adults with varying levels of physical activity at a singular time-point or at multiple time-points within a short duration of time (a few years) to examine potential associations with the onset of dementia. A meta-analysis of these  observed that individuals who exercised in midlife had a significantly reduced risk of later life mild cognitive impairment and onset of dementia-related disorders, such as Alzheimer’s. Specifically, the reduction of dementia risk associated with midlife exercise was 28% .
A recent intervention study in individuals aged 60 – 88 with and without mild cognitive impairment observed that walking for 30 minutes, 4 times per week for 3 months was related to improved memory . The group with mild cognitive impairment at the beginning of the study also had improved physiology in a brain region associated with memory loss and β-amyloid accumulation . This is in line with randomly controlled trials which, when analyzed in a meta-analysis, showed aerobic exercise in healthy adults was related to improved cognitive scores .
However, a recent longitudinal study which tracked 646 participants for 30 years reported that exercise in mid-life was not related to cognitive health in later life . The population of this study – medical students registered at a specific medical school between 1948 and 1964 – was rather homogenous and predominantly male, meaning any differences in cognition observed could be more confidently attributed to differences in exercise rather than other potentially confounding factors (i.e., socioeconomic status). This study did confirm findings of the previously mentioned prospective cohort studies, that exercise assessed closer in time to cognitive testing was associated with improved cognitive health. This finding potentially reflects reverse causality, or the possibility that individuals with early, preclinical neurodegenerative disorders may stop exercising as a direct result of the disorder itself . Consequently, these findings must be interpreted with caution.
Don’t quit your exercise regime! Although the jury is still out on exercise as a long-term preventative and treatment for neurodegenerative disorders, conclusive evidence shows that exercise is essential for cardiovascular health, optimal body composition, and maintenance of bone and lean mass.
The United States Department of Health and Human Services recommends that adults should participate in at least 2.5 hours of moderate-intensity aerobic physical activity per week in episodes of at least 10 minutes . This is a minimal recommendation and, for more extensive health benefits, further aerobic training is encouraged. Muscle-strengthening activities are also included in the guidelines, at a rate of at least twice per week.
Merritt Drewery is a native of Baytown, Texas. She holds a Bachelors of Science and Masters of Science in Animal Science, with a focus in Ruminant Nutrition, from Texas A&M University. Merritt recently received her PhD in Molecular and Clinical Nutrition from Louisiana State University. Her research interests include the role of perinatal nutrition in optimizing fetal and infant development, especially in infants born to women with adverse metabolic conditions. In her free time, she is probably playing with her very scruffy, disobedient dog or showing pictures of her nephews to anybody who will feign interest.
 CDC. US death rates from Alzheimer’s disease increased 55 percent from 1999 to 2014. https://www.cdc.gov/media/releases/2017/p0525-alzheimer-deaths.html. Accessed 9/10/2017.
 Adlard PA, Perreau VM, Pop V, Cotman CW. Voluntary exercise decreases amyloid load in a transgenic model of Alzheimer’s disease. J Neurosci 2005;25:4217-4221.
 Shankar GM, Li S, Mehta TH, et al. Amyloid-beta protein dimers isolated directly from Alzheimer’s brains impair synaptic plasticity and memory. Nature Med 2008;14:837-842.
 Pereira AC, Huddleston DE, Brickman AM, et al. An in vivo correlate of exercise-induced neurogenesis in the adult dentate gyrus. Proc Natl Acad Sci USA 2007;104:5638-5643.
 Hamer M, Chida Y. Physical activity and risk of neurodegenerative disease: a systematic review of prospective evidence. Psychol Med 2009;39:3-11.
 Chirles TJ, Reiter K, Weiss, LR, et al. Exercise training and functional connectivity changes in milk cognitive empairment and healthy elders. J Alzheimer’s Dis 2017;57:845-856.
 Smith PJ, Blumenthal JA, Hoffman BM, et al. Psychosom Med 2010;72:239-252.
 Gross AL, Lu H, Meoni L, Gallo JJ, Schrack JA, Sharrett AR. Physical activity in midlife is not associated with cognitive health in later life among cognitively normal older adults. J Alzheimer’s Dis 2017;59:1349-1358.
 Ahlskog JE, Geda YE, Graff-Radford NR, Petersen RC. Physical exercise as a preventative or disease-modifying treatment of dementia and brain aging. Mayo Clin Proc 2011;86:876-884.
 United States Department of Health and Human Services. 2008 Physical Activity Guidelines for Americans. https://health.gov/paguidelines/guidelines/summary.aspx. Accessed 9/10/2017.