OP40 Selenium Supplementation for the Primary Prevention of Cardiovascular Disease (CVD) – A Cochrane Systematic Review

Abstract

Background: Selenium is a key component of a number of selenoproteins with anti-oxidant properties, and may help to prevent chronic diseases including cardiovascular disease (CVD). However, observational studies have shown inconsistent associations between selenium status and CVD risk; in addition, there is concern about a potential diabetogenic effect of selenium supplementation in people of adequate or high selenium status. Objectives: To determine the effectiveness of selenium only supplementation for the primary prevention of CVD and examine potential adverse effects on type 2 diabetes. Methods: The following electronic databases were searched with no language restrictions from their inception to October 2011: MEDLINE, EMBASE, CINAHL, Web of Science, the Cochrane Library and trial registers. Studies were included if they fulfilled the following criteria: study design - randomized controlled trials (RCTs), participants - free of CVD (includes those at high risk), intervention - selenium only supplementation, comparator - no intervention or placebo, outcomes - diagnosis of CVD or change in the risk factor profile for CVD (blood pressure, lipids) or adverse effects (type 2 diabetes). Results: Database searching resulted in 1310 hits of which 43 went forward for formal inclusion/exclusion; 9 RCTs with 14 trial arms met the inclusion criteria with 19655 participants randomised. Included trials were heterogeneous in the participants recruited, dose of selenium, intervention and follow-up periods, outcomes reported, country of recruitment and baseline selenium status. Meta-analysis was possible for 2 trials reporting clinical events, but the analysis was dominated by the SELECT trial which carried over 80% of the weight. There were no statistically significant effects of selenium supplementation on all-cause mortality (RR 0.97, 95% CI 0.88, 1.08), CVD mortality (RR 0.97, 95% CI 0.79, 1.2), non-fatal CVD events (RR 0.96, 95% CI 0.89, 1.04) or all CVD events (fatal and non-fatal, RR 1.03, 95% CI 0.95, 1.11). There was a small increased risk of type 2 diabetes with selenium supplementation but this did not reach statistical significance (RR 1.06, 95% CI 0.97, 1.15). Selenium supplementation reduced total cholesterol but this did not reach statistical significance (WMD -0.11 mmol/L, 95% CI -0.3, 0.07). Mean HDL levels were unchanged. There was a statistically significant reduction in non-HDL cholesterol (WMD -0.2 mmol/L, 95% CI -0.41, 0.00) in one trial of varying selenium dosage. None of the trials examined effects on blood pressure. Conclusions: There is still limited trial evidence supporting the effect of selenium supplementation on CVD events, lipid levels and type 2 diabetes in the primary prevention of CVD. Additional evidence is needed especially to clarify the potential adverse effect of selenium supplementation on type 2 diabetes.