The role of glucose in cognition, risk of dementia, and related biomarkers in individuals without type 2 diabetes mellitus or the metabolic syndrome: A systematic review of observational studies.

BACKGROUND: Excessive blood glucose promotes neuropathological cognitive decline in individuals with type 2 diabetes mellitus and the metabolic syndrome, but no systematic synthesis of the evidence for the same association exists in individuals without these conditions. OBJECTIVES: To systematically review studies exploring the role of glucose on cognition, dementia risk, and related biomarkers in adults without diabetes or metabolic syndrome. DATA SOURCES: We searched databases from inception until July 2021 and manually searched the reference lists of included studies. Risk of bias was assessed using the Joanna Briggs Institute tool. RESULTS: We found 46 observational studies including approximately 98,216 participants. Substantial heterogeneity in study results precluded drawing definitive conclusion whether blood glucose levels are associated with cognition or dementia risk. Higher blood glucose, however, was associated with greater amyloid burden, brain atrophy, and reduced cortical thickness. CONCLUSIONS AND IMPLICATIONS: High glucose concentrations in blood may exacerbate dementia-related neuropathology but whether this translates into pathological cognitive decline or elevate dementia risk later in life remains unclear.

Association of mental disorders with firearm suicides: A systematic review with meta-analyses of observational studies in the United States.

BACKGROUND: In the United States (US), 61% of all suicide cases may involve firearms, and some evidence suggests that mental disorders may play a role in suicide by firearm. We performed the first systematic review and meta-analyses to investigate: (i) whether mental disorders are associated with suicide by firearm, and (ii) whether the risk of using a firearm compared with alternative means is associated with higher levels of suicide in individuals with a mental disorder METHODS AND FINDINGS: We searched twelve databases from inception to the 24th of May 2020. We retrieved 22 observational studies conducted in the US. Random-effects meta-analyses showed individuals who had a diagnosis of a mental disorder had lower odds (odds ratios (OR)= 0.50, 95% CI: 0.36 to 0.69; I2=100 (95% CI: 87 to 100%), of dying by suicide with a firearm than those who did not have a diagnosis of a mental disorder. Secondary analysis showed that decedents who had a mental health diagnosis resulted in lower odds of dying by suicide by using firearms than using other means LIMITATIONS: Risk of bias revealed a heterogeneous and poor definition of mental disorders as well as lack of control for potential demographic confounding factors. In the meta-analyses, studies were combined in the same analytic sample as 77% of these studies did not specify the type of mental disorder CONCLUSION: While our results seem to suggest that having a mental disorder may not be consistently associated with the odds of dying by suicide using a firearm, the presence of substantial heterogeneity and high risk of bias precludes any firm conclusions.