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, Reference Barnes and Yaffe2011). 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.

In this month's issue of International Psychogeriatrics, Farina and colleagues (Reference Farina, Rusted and Tabet2013) publish a systematic review with the title “The effect of exercise interventions on cognitive outcome in Alzheimer's disease: a systematic review.”. This paper will help the reader of International Psychogeriatrics to critically review the evidence for physical activity and cognition provided by RCTs in patients with AD. The authors included six RCTs published between 2004 and 2012 in their meta-analysis by including four of them in the analysis regarding cognitive function. These four studies were associated with an effect size of 1.12 (95% CI = 0.37–1.88). Following a sensitivity analysis, one further study was removed from the meta-analysis resulting in a new effect size of 0.75 (95% CI = 0.32–1.17), which still is significantly in favor of physical activity. This finding is encouraging and should be considered as another piece of evidence to encourage physical activity for older adults with AD.

But what do these three RCTs in this review have in common? Mainly that they involve patients with AD and are of good quality standards. Otherwise there were differences regarding type, intensity, and length of the interventions, choice of control group, and outcome measures. So while the overall positive result of this systematic review is promising, the limitations when interpreting this finding are plentiful, which Farina and colleagues (Reference Farina, Rusted and Tabet2013) thoroughly discuss in their paper. Most importantly, the number of studies included and the number of participants in these studies are small, which is a reminder that this area of research is still in its infancy. The editorial team of International Psychogeriatrics selected this systematic review as paper of the month, since next to reviewing the evidence it discusses in detail what further research is needed in this important area. We also want to encourage other authors who consider writing systematic reviews in the field of psychogeriatrics to consider a submission to International Psychogeriatrics.