Is vitamin C supplementation beneficial? Lessons learned from randomised controlled trials

In contrast to the promised ‘antioxidant miracle’ of the 1980s, several randomised controlled trials have shown no effect of antioxidant supplements on hard endpoints such as morbidity and mortality. The former over-optimistic attitude has clearly called for a more realistic assessment of the benefit:harm ratio of antioxidant supplements. We have examined the literature on vitamin C intervention with the intention of drawing a conclusion on its possible beneficial or deleterious effect on health and the result is discouraging. One of several important issues is that vitamin C uptake is tightly controlled, resulting in a wide-ranging bioavailability depending on the current vitamin C status. Lack of proper selection criteria dominates the currently available literature. Thus, while supplementation with vitamin C is likely to be without effect for the majority of the Western population due to saturation through their normal diet, there could be a large subpopulation with a potential health problem that remains uninvestigated. The present review discusses the relevance of the available literature on vitamin C supplementation and proposes guidelines for future randomised intervention trials.