Gender-Specific Design and Effectiveness of Non-Pharmacological Interventions against Cognitive Decline - Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: The number of people living with dementia worldwide is increasing rapidly. Preventive approaches constitute a promising strategy to counter the dementia epidemic, and growing numbers of lifestyle interventions are conducted around the globe. Gender differences with respect to modifiable risk factors for dementia have been reported, however, little is known about gender-specific effectiveness of lifestyle trials against cognitive decline and dementia. A systematic review and meta-analysis was conducted to assess evidence on gender-specific design and effectiveness of randomized controlled trials against cognitive decline.

Methods: Systematic literature searches were conducted in MEDLINE, PsycINFO, Web of Science, Cochrane Central and ALOIS. Studies assessing global and/or domain-specific cognitive function in older adults free from dementia were eligible for the systematic review. We assessed between-group effect sizes using random-effects meta-analysis. Methodological quality of included studies was assessed using the Scottish Intercollegiate Guidelines Network (SIGN)-checklist.

Results: The systematic review and meta-analysis included 34 and 31 studies, respectively. Effects of lifestyle-interventions on global cognition were non-significant overall (g = .27; 95% CI: -.01; .56) and in male subsamples (g = -.05; 95% CI: -.55; .45), and small for female subsamples (g = .38; 95% CI: .05; .72). Small beneficial effects were found for memory (overall: g = .38; 95% CI = .17; .59). Stratified by gender, significant effects were observed only in women (g = .39; 95% CI = .13; .65; men: g = .37; 95% CI: .00; .73). Aspects of gender in study design and conduct were discussed in a small minority of studies. Comparable results were observed for executive function and verbal fluency. Methodological quality was deemed high in 17.6% of studies, acceptable and low quality in 52.9% and 29.4%, respectively.

Discussion: We found evidence for small differences in the effectiveness of lifestyle interventions on global cognition and memory in favor of women. However, small numbers of trials 1) targeting men and 2) reporting gender-specific results for older adults with mild cognitive impairment warrant further attention. Assessing differences in modifiable risk factors for dementia in men and women and systematically addressing aspects of gender in trial conduction and recruitment in future studies might increase knowledge on gender-specific effectiveness of lifestyle trials against cognitive decline.