Circulating tocopherols and risk of coronary artery disease: A systematic review and meta-analysis

Background Circulating level of tocopherols was supposed to be associated with risk of coronary artery disease. However, the results from previous studies remain controversial. Therefore, we conducted a meta-analysis based on observational studies to evaluate the association between circulating tocopherols and coronary artery disease risk for the first time. Design Meta-analysis. Methods PubMed, Embase and Cochrane databases were searched to retrieve articles published during January 1995 and May 2015. Articles were included if they provided sufficient information to calculate the weighted mean difference and its corresponding 95% confidence interval. Results Circulating level of total tocopherols was significantly lower in coronary artery disease patients than that in controls (weighted mean difference -4.33mol/l, 95% confidence interval -6.74 to -1.91, P<0.01). However, circulating -tocopherol alone was not significantly associated with coronary artery disease risk. Results from subgroup analyses showed that a lower level of circulating total tocopherols was merely associated with higher coronary artery disease risk in studies with higher sex ratio in cases (<2, weighted mean difference -0.07mol/l, 95% confidence interval -1.15 to 1.00, P=0.90;2, weighted mean difference -6.00mol/l, 95% confidence interval -9.76 to -2.22, P<0.01). Similarly, a lower level of circulating total tocopherols was associated with early onset coronary artery disease rather than late onset coronary artery disease (<60 years, weighted mean difference -5.40mol/l, 95% confidence interval -9.22 to -1.57, P<0.01;60 years, weighted mean difference -1.37mol/l, 95% confidence interval -3.48 to 0.74, P=0.20). We also found some discrepancies in circulating total tocopherols when the studies were stratified by matching status and assay methods. Conclusions Our findings suggest that a deficiency in circulating total tocopherols might be associated with higher coronary artery disease risk. Whereas circulating -tocopherol alone could not protect us from developing coronary artery disease. Further prospective studies were warranted to confirm our findings.