The association of depression and all-cause and cause-specific mortality: an umbrella review of systematic reviews and meta-analyses

Background: Depression is a prevalent and disabling mental disorder that frequently co-occurs with a wide range of chronic conditions. Evidence has suggested that depression could be associated with excess all-cause mortality across different settings and populations, although the causality of these associations remains unclear. Methods: We conducted an umbrella review of systematic reviews and meta-analyses of observational studies. PubMed, PsycINFO, and Embase electronic databases were searched through January 20, 2018. Systematic reviews and meta-analyses that investigated associations of depression and all-cause and cause-specific mortality were selected for the review. The evidence was graded as convincing, highly suggestive, suggestive, or weak based on quantitative criteria that included an assessment of heterogeneity, 95% prediction intervals, small-study effects, and excess significance bias. Results: A total of 26 references providing 2 systematic reviews and data for 17 meta-analytic estimates met inclusion criteria (19 of them on all-cause mortality); data from 246 unique studies (N = 3,825,380) were synthesized. All 17 associations had P < 0.05 per random effects summary effects, but none of them met criteria for convincing evidence. Associations of depression and all-cause mortality in patients after acute myocardial infarction, in individuals with heart failure, in cancer patients as well as in samples from mixed settings met criteria for highly suggestive evidence. However, none of the associations remained supported by highly suggestive evidence in sensitivity analyses that considered studies employing structured diagnostic interviews. In addition, associations of depression and all-cause mortality in cancer and post-acute myocardial infarction samples were supported only by suggestive evidence when studies that tried to adjust for potential confounders were considered. Conclusions: Even though associations between depression and mortality have nominally significant results in all assessed settings and populations, the evidence becomes weaker when focusing on studies that used structured interviews and those that tried to adjust for potential confounders. A causal effect of depression on all-cause and cause-specific mortality remains unproven, and thus interventions targeting depression are not expected to result in lower mortality rates at least based on current evidence from observational studies

Comparison of phenotypic diversity and DNA heterogeneity in a population of soil bacteria.

The phenotypic diversity of about 200 bacterial strains isolated from soil was compared with the genotypic diversity of the same population. The strains were phenotypically characterized by the API 20B test system. The results of these tests were subjected to cluster analysis, which revealed 41 biotypes at 80% similarity. The five dominating biotypes contained 43% of the strains. The phenotypic diversity as determined by the Shannon index, equitability, rarefaction, and cumulative differences was high, but indicated some dominant biotypes. The genetic diversity was measured by reassociation of mixtures of denatured DNA isolated from the bacterial strains (C0t plots). The observed genetic diversity was high. Reassociation of DNA from all bacterial strains together revealed that the population contained heterologous DNA equivalent to 20 totally different bacterial genomes (i.e., genomes that have no homology). This study showed that reassociation of DNA isolated from a collection of bacteria gave a good estimate of the diversity of the collection and that there was good agreement with different phenotypic diversity measures. The Shannon index in particular has features in common with the genetic diversity measure presented here