Vitamin C intake, circulating vitamin C and risk of stroke: a meta-analysis of prospective studies.

Though vitamin C supplementation has shown no observed effects on stroke prevention in several clinical trials, uncertainty remains as to whether long-term, low-dose intake influences the development of stroke among general populations. Furthermore, the association between circulating vitamin C and the risk of stroke is also unclear. For further clarification of these issues, we conducted a meta-analysis of prospective studies. PubMed and EMBASE databases were searched, and the bibliographies of the retrieved articles were also reviewed to identify eligible studies. Summary relative risk (RRs) with corresponding 95% confidence intervals (CIs) were computed with a random-effects model. The summary RR for the high-versus-low categories was 0.81 (95% CI: 0.74 to 0.90) for dietary vitamin C intake (11 studies), and 0.62 (95% CI: 0.49 to 0.79) for circulating vitamin C (6 studies). The summary RR for each 100 mg/day increment in dietary vitamin C was 0.83 (95% CI: 0.75 to 0.93) (10 studies), and for each 20 μmol/L increment in circulating vitamin C was 0.81 (95% CI: 0.75 to 0.88) (5 studies). Few studies reported results for vitamin C supplements (RR for high-versus-low intake=0.83, 95% CI: 0.62 to 1.10, 3 studies). This meta-analysis suggests significant inverse relationships between dietary vitamin C intake, circulating vitamin C, and risk of stroke.