The active metabolite of vitamin D, 1,25-dihydroxy-vitamin D, is able to cross the blood-brain barrier and is found in the human brain. Vitamin D is believed to be important in the process of neurodevelopment and the causation of neuropsychiatric disorders (2). In general, the incidence of vitamin D deficiency is higher in people suffering from psychotic disorders than the population at large (3). However, the strongest links between low vitamin D status and mental illness have previously been found in those people who have been suffering depression (4).
A fresh study from South Norway of 358 patients (part of the Thematically Organised Psychosis or TOP cohort) who have suffered one or more psychotic episodes has revealed a strong association between low blood vitamin D levels (measured as plasma S-25(OH)D) and increased negative psychotic symptoms and depression (1). Roughly two thirds of the patients were diagnosed as being in the schizophrenic spectrum, while roughly one third were diagnosed as bipolar. Negative psychotic symptoms are those where there is a loss of positive interpersonal communication functions, including lack of emotions, monotonic speech, lack of interest in other people, lack of ideas and lack of spontaneity. This association has been seen in two previous smaller studies (5, 6). This finding is important, as these negative psychotic symptoms are particularly difficult to treat and are very distressing for the patient.
The association between low vitamin D serum levels and depression/negative psychotic symptoms was particularly strong when measurements were made in the winter months and among those of non-Nordic ethnic origin, where presumably the majority have relatively highly pigmented skin. The lack of sun exposure and high skin melatonin levels are both known to depress serum vitamin D levels. It has recently been shown that vitamin D is important in serotonin synthesis because the lack of it will cause depression (7).
While the findings of the Norwegian studies are important, it is now necessary to conduct an intervention trial among patients suffering psychosis with the aim of determining whether their symptoms can be reduced.