Background: Laboratory and some epidemiological studies suggest that antioxidants, such as vitamin C, are protective for cardiovascular disease. This protective effect may be mediated through blood pressure (BP). This is the first systematic review of epidemiological studies of vitamin C and BP.
Method: Published cross-sectional studies, prospective studies and trials in humans were identified that examined the association between vitamin C intake or plasma vitamin C levels and BP. Relevant references were located by MEDLINE search 1966-1996, EMBASE search 1980-1996, by searching personal bibliographies, books and reviews and from citations in located articles.
Results: Cross-sectional data were available from 18 populations. Ten of 14 reported an inverse association between plasma vitamin C and BP and three of four reported an inverse association with vitamin C intake. The two non-randomised and four randomised controlled trials were all small. Of the randomised trials one reported a significant decrease in BP, one a non-significant decrease and two were uninterpretable.
Conclusions: We found a consistent cross-sectional association between higher vitamin C intake or status and lower BP, though no study controlled adequately for confounding by other dietary factors. Further cross-sectional studies are required to establish whether an independent association exists. If this is shown to be the case larger and longer term trials will be needed to confirm the association is causal. Potentially the impact on cardiovascular disease of a modest change in mean population vitamin C intake is large.