According to the World Health Organisation, more than one billion people suffer from a mental or behavioural disorder. It has been estimated that more than 300 million people in the world, i.e., 4.4% of the global population, suffer from depression. Schizophrenia has a prevalence of 4 to 7 per 1000 people, thus affecting about 20 million people. It follows that not only does treating such a large number of people represent a significant economic effort for the entire healthcare system it also constitutes a challenge for the entire medical sector, given the impact of these illnesses on several clinical fields.
Many scientific findings have clearly shown an association between vitamin D deficiency and depression or schizophrenia. Vitamin D, which is found in the human brain, has been identified as one of the key factors in the regulation of many neurotransmission pathways, including those of dopamine, serotonin, noradrenaline and glutamine. Recent studies have shown that vitamin D deficiency is associated with dysfunction of the hippocampus, a region involved in the pathogenesis of mental disorders, whilst it has also been positively correlated with grey matter volume.
Nevertheless, the causal relationship between vitamin D and mental disorders is still unclear. Even though it has been observed [1].
The aim of this study is to summarise the main scientific findings on the association between vitamin D deficiency and mental disorders, in order to increase the level of knowledge available to clinicians in all fields of medicine as well as to stimulate scientific production and experimental observation on this subject. Indeed, the establishment of a causal relationship would make it possible to understand whether and to what extent vitamin D supplementation might prevent the onset of mental disorders or reduce their symptoms.