Systematic evaluation of the associations between mental disorders and dementia: An umbrella review of systematic reviews and meta-analyses

Background: Increasing evidence support the correlation between mental disorders and the likelihood of developing dementia. We aim to conduct an umbrella review to assess the risk of dementia in patients with eight mental disorders. Methods: We searched PubMed, Embase, Web of science, CNKI, VIP, and Wanfang databases from inception to October 29, 2021. For each included meta-analysis, the effect size with a 95% confidence interval was estimated using either a random effect model or a fixed effect model, and between-study heterogeneity was expressed by I-2 and Cochran's Q test. The ROBIS tool was used to assess the risk of bias. Results: A total of ten systematic reviews were included. Among these studies, we identified seven risk factors, including anxiety disorder, bipolar disorder, depression, late-life depression, post-traumatic stress disorder, schizophrenia, and sleep disorder. Light to moderate alcohol drinking was identified as a protective factor. The evaluation results of the ROBIS tool showed that nine systematic reviews had high risk of bias and one had low risk of bias. The strength of evidence supporting the associations between late-life depression and all-cause dementia, Alzheimer's disease, and vascular dementia was high; the strength of evidence supporting the association between depression and all-cause dementia was moderate. Limitations: Most associations had low strength of evidence and high risk of bias. Conclusions: This umbrella review shows that high and moderate evidence supports the associations between some mental disorders and dementia. More cohort studies are needed to support the associations between mental disorders and dementia.