Physical activity in Alzheimer's disease: research in its infancy or why we need more randomized controlled trials

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With the global aging of our societies and predicted increase of cognitive impairment and dementia, it is no surprise that there is an increasing interest in the research community, but also among clinicians and the general population to learn more about how to focus on modifiable protective factors and how to avoid modifiable risk factors. A recent review of systematic reviews and meta-analyses on significant risk factors for Alzheimer's disease (AD) highlighted the importance of diabetes, hypertension, obesity, smoking, depression, cognitive inactivity, and physical inactivity (Barnes and Yaffe, 2011). For physical inactivity, for example, the authors reported that up to one million cases of AD could be prevented globally if a physical inactivity could be reduced by 25%. However, we should not forget about the various stages of prevention, and especially in the field of psychogeriatrics should also ask what preventative measures might be effective for older adults who have already experienced cognitive impairment. So we could focus on a secondary prevention approach for individuals with mild cognitive impairment (MCI) or on a tertiary preventative approach for patients with dementia. The number of randomized controlled trials (RCT) investigating the effectiveness of physical activity on cognition is limited for healthy participants and those with MCI, but is even more sparse for those with dementia. Even with the limited number of studies it often is difficult to compare RCTs due to the huge variation in inclusion and exclusion criteria, methodology, instruments used and outcomes, intervention and duration of interventions, and observations.