Les supplémentations vitaminiques systématiques : ont-elles une place dans la prévention des maladies chroniques ?

Besides treatments of well documented vitamin deficiencies, specific or multivitamin supplementations were hypothesized to help to prevent chronic cardiovascular diseases and some cancers, or even to cure such clinical disorders. This hypothesis was mainly based on data generally provided by poorly designed observational and epidemiologic studies. Unfortunately, the purported benefits of vitamin supplementations were further never confirmed during controlled randomized interventional trials. Several studies have even suggested that supplementations with such vitamins as A and E may play a consistent role in precipitating the occurrence of deleterious clinical outcomes. Consequently, it seems reasonable to avoid any utilization of vitamin supplements when there is no incontrovertible evidence for insufficiency, and when circulating plasma levels of vitamins remain within the normal range. However, it should be noted that, for many vitamins, plasma assays are neither routinely available nor reliable. For instance, since many years there is an endless debate to know as how to assess the vitamin D status in the general population and to define the levels at which plasma 25-hydroxy (OH)-vitamin D concentration, the usual marker of this status, should be set. Bringing all these observations together, it appears that systematic supplementations with vitamins should be only limited to persons who are at risk of vitamin deficiencies, such as the individuals (younger or older) who are not sufficiently exposed to sunlight, the subjects who have undergone a bariatric surgery, the pregnant women considered to be 'vulnerable', and the patients submitted to either a chronic artificial parenteral or enteral feeding. Once again, we must outline that treatments with vitamins should be prescribed with caution because unwarranted supplementation with amounts of vitamins largely above their usual Recommended Dietary Allowances (RDAs) can be a causative factor for harmful effects. This is particularly true for vitamin A and D, and at a lesser degree for vitamin E.