The biological plausibility of vitamin D deficiency as a risk factor for schizophrenia is supported by the expression of the vitamin D receptor (VDR) and 25-hydroxyvitamin D-1α-hydroxylase (an enzyme required for 1,25-dihydroxyvitamin D (1,25(OH)2D) production) in the human brain15. This evidence concerns the gene VDR and vitamin D deficiency.