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Endothelial dysfunction is caused by excessive free radical production and nitric oxide (NO) inadequacy. Endothelial dysfunction is the primary cause of vascular disorders and is related to the progression of clinical complications. Human trials examining the effects of antioxidant vitamins on endothelial function (EF) showed inconclusive results. We undertook as systematic review and meta-analysis of the evidence from randomised controlled trials (RCTs) for effects of supplementation with vitamins C and E on EF. We searched the Medline, Embase, Scopus and the Cochrane Library databases for studies that met the following criteria: 1) RCTs with adult participants, 2) vitamin C or E administered alone or in combination, 3) studies that quantified EF using forearm blood flow or flow mediated dilation. EF responses across studies were pooled as standardised mean differences and analysed using a random-effects model using STATA 12 (StataCorp. 2011. College Station, TX, USA). Meta-analysis showed a significant improvement in EF in trials supplementing with vitamins C (SMD: 0·25, 95% CI: 0·02, 0·49, P= 0·043) and E (SMD: 0·48, 95% CI: 0·23, 0·72, P= 0·0001) alone whereas the co-administration of both vitamins was ineffective (SMD: 0·12, 95% CI: −0·18, 0·42, P= 0·428). The effect of vitamin C on EF increased with participant age (β: 0·023, CI: 0·001, 0·05, P= 0·042). There was as significant negative correlation between baseline plasma vitamin E concentration and the EF response to vitamin E (β: −0·03, CI: -0·06, −0·001, P= 0·029). Separate supplementation with vitamins C and E improves EF. Furthermore, subgroup analysis emphasises the importance of careful selection of the population group which may benefit from such supplementation.

Ourobjective was to conduct a systematic review and meta-analysis investigating the effect of antioxidant vitamins on arterial stiffness.The second objective was to determine whether the effects on arterial stiffness vary according to dose of antioxidant vitamins, durationof intervention, and health or nutritional status of the included participants.We searched 3 databases (Medline, Embase and Scopus) for articles with the following criteria: 1) randomized controlled trialscomparing antioxidant vitamins (vitamins C, E, A, beta-carotene) with either placebo or no active control; 2) adult participants⩾18 years; 3) antioxidant vitamins administered alone or in combination; 4) changes in arterial stiffness or arterial compliance.Data were pooled as standardized mean difference (SMD) and analysed using a fixed effects model.Pooled analysis (20 studies, 1,909 participants) showed that antioxidant vitamins supplementation reduced arterial stiffness sign-ificantly (SMD: −0·17, 95% CI: −0·26, −0·08, P=0·0001). This effect was significant in both experimental and primary preventionstudies but not in studies including participants with diseases (SMD: −0·19, 95% CI: −0·40, −0·02, P=0·081). Vitamins supplemen-tation improved arterial stiffness irrespective of age group and duration of intervention. Antioxidant vitamins were more effective inparticipants with low baseline plasma concentrations of vitamin C and E.In conclusion, supplementation with antioxidant vitamins has a small, protective effect on arterial stiffness. The effect may be aug-mented in those with lower baseline plasma vitamin E and C concentrations.