Sex Differences in Depression as a Risk Factor for Alzheimer’s Disease: A Systematic Review

BACKGROUND AND OBJECTIVES: Depression is an important risk factor for Alzheimer’s disease (AD) but little is known about the mechanisms of this association. Given sex differences in both AD and depression, we sought to conduct a systematic review and meta-analysis to examine whether there are sex differences in their association, as this may improve understanding of underlying mechanisms. RESEARCH DESIGN AND METHODS: MEDLINE, PsycINFO, and Cochrane Reviews were searched for observational studies including both sexes and examining the association between history of depression and AD. RESULTS: Forty studies, including 62,729 women and 47,342 men, were identified. Meta-analysis was not possible because only 3 studies provided sufficient data. Seven studies provided information about the influence of sex for a qualitative synthesis. Two found an association in men only, 2 in women only, and 3 reported no sex differences. The 2 studies finding an association in women only were unique in that they had the shortest follow-up periods, and were the only clinic-based studies. DISCUSSION AND IMPLICATIONS: The findings of our systematic review show that there are important methodological differences among the few studies providing data on the influence of sex on depression as a risk factor for AD. Had all 40 studies provided sex-segregated data, these methodological differences and their impact on sex effects could have been examined quantitatively. We encourage researchers to report these data, as well as potential moderating factors, so that the role of sex differences can be better understood.