The effect of exercise interventions on cognitive outcome in Alzheimer's disease: a systematic review

BACKGROUND: Non-pharmacological interventions may have a role in both the prevention and slowing down of disease progression in Alzheimer's disease (AD). The role of exercise in disease prevention, for example, has been extensively evaluated in large epidemiological studies. Much less is known about the potential benefit of exercise in patients already diagnosed with AD. It was therefore the aim of this systematic review to assess the effectiveness of exercise in attenuating cognitive decline within AD. METHOD: A systematic review was conducted statistically accompanied by a meta-analysis. Publications between January 1991 and October 2012 were identified by searching the electronic databases PubMed, Science Direct, Web of Knowledge, and PsychINFO. Selected studies required AD patients to take part in an exercise-based randomized controlled trial (RCT) and have a cognitive outcome measure. RESULTS: Six RCTs were identified that exclusively considered the effect of exercise in AD patients. Exercise generally had a positive effect on rate of cognitive decline in AD. A meta-analysis found that exercise interventions have a positive effect on global cognitive function, 0.75 (95% CI = 0.32-1.17). CONCLUSIONS: From the six studies reviewed, the evidence suggests that exercise can have a positive effect on rate of cognitive decline in AD. However, the variation between study designs makes conclusions regarding the optimum intervention on cognitive outcome in AD difficult. Well-designed and powered RCTs are still needed to ascertain the efficacy of exercise in slowing down cognitive impairment in AD patients. However, a positive initial indication for exercise efficacy justifies such efforts.