The effect of co-administration of vitamin E and C supplements on plasma oxidative stress biomarkers and antioxidant capacity: a GRADE-assessed systematic review and meta-analysis of randomized controlled trials with meta-regression

Abstract

<bold>Background:</bold> There is no conclusion on the effect of vitamins E and C on plasma biomarkers of oxidative stress and antioxidant status. We conducted this meta-analysis to gain a clearer view of this area. <bold>Methods:</bold> We performed a systematic search in online databases using the relevant keyword combination. Randomized controlled trials that investigated the effect of vitamins E and C simultaneously, compared with control, on oxidative stress and antioxidant status biomarkers were included in the analyses. <bold>Results:</bold> A total of 17 trials were included in the meta-analysis, building a total sample size of 965. The dosage of vitamin E and C supplements varied from 54 to 536 and 250 to 1000 mg/d, respectively, across included studies. We found significant results for MDA WMD: -0.38, 95% CI: -0.48, -0.28 mu g/L, P <0.001, LP WMD: -1.01, 95% CI: -1.49, -0.54 <mu>g/L, P <0.001, TAC WMD: 0.09, 95% CI: 0.05, 0.13 mmol/L, P <0.001, and GPx WMD: 1251.74, 95% CI: 258.92, 2244.56 U/L, P = 0.013, but not for SOD WMD: 16.69, 95% CI: -29.40, 62.78 U/L, P = 0.278. Regarding subgroup analysis, only studies on unhealthy participants showed a significant effect on MDA WMD: -1.62, 95% CI: -2.08, -1.15 mu g/L, P <0.001 and TAC WMD: 0.08, 95% CI: 0.03, 0.14 mmol/L, P <0.001, unlike LP, where significance was only observed in healthy adults WMD: -0.41, 95% CI: -0.45, -0.37 mu g/L, P <0.001. Moreover, only studies in which a placebo was administered, supplementation of vitamins showed significant effects on MDA WMD: -0.47, 95% CI: -0.58, -0.35 <mu>g/L, P <0.001, LP WMD: -1.28, 95% CI: -1.85, -0.72 <mu>g/L, P <0.001, and TAC WMD: 0.10, 95% CI: 0.05, 0.15 mmol/L, P <0.001. <bold>Conclusion:</bold> Our review and analyses revealed that a combination of vitamin C and E has a beneficial effect on oxidative stress biomarkers and antioxidant status.