Vitamin C Intake, Circulating Vitamin C and Risk of Stroke: A Meta-Analysis of Prospective Studies

Background-—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. Methods and Results-—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 lmol/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). Conclusions-—This meta-analysis suggests significant inverse relationships between dietary vitamin C intake, circulating vitamin C