Aim: To carry out a meta-analysis of population-based prospective cohort studies to investigate the risk of dementia and Alzheimer's disease (AD) according to clinically relevant depression, assessed with Geriatric Mental State (GMS) criteria.

Patients and methods: A systematic literature search of the studies published in PubMed and Web of Science up to January 2018 was performed to identify all longitudinal studies on the association between clinically relevant depression (diagnosed with GMS criteria) and risk of dementia in the elderly. We calculated pooled relative risks to examine depression as a possible risk factor for dementia in community studies, as well as to compute population attributable fraction (PAF).

Results: Six studies met inclusion criteria for the systematic review. All of them provided enough information to perform a meta-analysis. Participants with clinically relevant depression had a 54% higher risk of dementia (p = 0.026) with a PAF attributable to clinically relevant depression of 8.6%. The numbers for AD were 50% higher risk (p = 0.038) and a PAF of 10.8%.

Conclusion: Clinically relevant depression is associated with an increased risk for dementia and AD in the community, with a potential impact higher than other known/recognized risk factors. Future studies should explore the mechanisms linking depression and dementia and AD as well as whether an effective treatment of clinically significant depression could prevent dementia and AD development.