[What is a vitamin?].

In industrialized countries, the major vitamin deficiency syndromes have virtually disappeared. Today they are superseded by marginal deficits, characterized by insufficient vitamins reserves to maintain normal physiologic state. These states strike populations such as infants, pregnant women, alcoholics and the elderly, and may have long-term adverse effects on health. This assumption stems from the analysis of studies that show an increase in the incidence of various diseases such as cancers and cardiovascular, ocular and osteoarticular pathologies in subjects with low vitamin status. Although causal relationships are difficult to establish, a huge scope for public health appears to be open for vitamins, substituting the notion of minimal intake, indispensable to prevent signs of deficiency, to that ensuring optimal health in the medium and long-terms. However, the paradoxical character of the results obtained in several randomized trials should prompt caution in the use of vitamin supplements to prevent chronic diseases.