Quite recently, a growing number of studies have shown the extra-skeletal effects of vitamin D, especially in maintaining immunological homeostasis and preserving the intestinal barrier. As a result, the hypothesis of the involvement of vitamin D in the pathogenesis of many immune-mediated conditions seems now plausible. Among these, coeliac disease is a chronic inflammatory condition targeting the small intestine, that is triggered and sustained by the ingestion of gluten contained in some cereals by genetically susceptible individuals. Coeliac disease is the world’s most frequent noncommunicable illness, whose prevalence ranges between 0.5 and 1.0%. However, in spite of the high – if not absolute – reliability of diagnostic tests, its real prevalence is much lower (roughly 1‰) due to the variability of clinical features, including pauci-symptomatic cases, that is coupled with the limited knowledge of this condition among general practitioners. This generates the so-called “iceberg” phenomenon, in which diagnosed cases represent only the upper visible fraction of the total. In any case, our current understanding strongly recommends evaluation of serum vitamin D levels in both young and adult patients with coeliac disease, given that both the enteropathy and the possible bacterial overgrowth of the small intestine can lead to malabsorption of vitamin D, with obvious consequences on bone health. In addition, recent studies have proven its immunomodulatory role on all cell populations involved in immune response, while protecting the intestinal barrier and regulating the enterokinesis. Vitamin D deficiency may, therefore, represents an environmental factor that, together with gluten and genetic predisposition, is necessary for triggering and maintaining intestinal lesions in this pathological condition.
