A systematic review and meta-analysis of the circulatory, erythrocellular and CSF selenium levels in Alzheimer's disease: A metal meta-analysis (AMMA study-I)

Background: Available studies in the literature on the selenium levels in Alzheimer's disease (AD) are inconsistent with some studies reporting its decrease in the circulation, while others reported an increase or no change as compared to controls. Aim The objective of this study was to perform a meta-analysis of circulatory (plasma/serum and blood), erythrocyte and cerebrospinal fluid (CSF) selenium levels in AD compared controls. We also performed a meta analysis of the correlation coefficients (r) to demonstrate the associations between selenium and glutathione peroxidase (GPx) in AD patients. Methods: All major databases were searched for eligible studies. We included 12 case-control/observational studies reporting selenium concentrations in AD and controls. Pooled-overall effect size as standardized mean difference (SMD) and pooled r-values were generated using Review Manager 5.3 and MedCalc 15.8 software. Results: Random-effects meta-analysis indicated a decrease in circulatory (SMD = -0.44), erythrocellular (SMD = -0.52) and CSF (SMD = -0.14) selenium levels in AD patients compared to controls. Stratified meta analysis demonstrated that the selenium levels were decreased in both the subgroups with (SMD = -0.55) and without (SMD = -0.37) age matching between AD and controls. Our results also demonstrated a direct association between decreased selenium levels and GPx in AD. Conclusion: This meta-analysis suggests that circulatory selenium concentration is significantly lower in AD patients compared to controls and this decrease in selenium is directly correlated with an important antioxidant enzyme, the GPx, in AD.