Depressive Symptoms in Mild Cognitive Impairment and the Risk of Dementia: A Systematic Review and Comparative Meta-Analysis of Clinical and Community-Based Studies.

Abstract

Affective symptoms are considered a risk factor or prodromal symptom for dementia. Recent reviews indicate that depressive symptoms predict progression from mild cognitive impairment (MCI) to dementia, but results need to be further explored. To investigate the effect of depressive symptoms on the development of dementia in people with MCI, and explore potential sources of between-study variability, including study setting by a systematic review and meta-analysis. Databases were searched for prospective studies defining people with MCI at baseline, investigating dementia at follow-up and giving information about depressive symptoms. Two authors independently extracted data from the studies and rated the methodological quality. Meta-analyses were conducted using random-effect models to yield pooled risk ratios (RR). Meta-regression analyses tested differences between clinical and community-based studies and other sources of heterogeneity. Thirty-five studies, representing 14,158 individuals with MCI, were included in the meta-analysis. Depressive symptoms in MCI predicted dementia in 15 community-based studies (RR = 1.69, 95% CI 1.49-1.93, I2 = 0.0%), but not in 20 clinical studies (RR = 1.02, 95% CI 0.92-1.14, I2 = 73.0%). Further investigation of this effect showed that the mean age of community-based studies was significantly higher than of clinical studies but neither this nor other study characteristics explained variability in study outcomes. Depressive symptoms are associated with an increased risk of conversion from MCI to dementia in community-based studies. In contrast, evidence in clinical populations was insufficient with high heterogeneity.