VDR and vitamin D deficiency: Of the 14 articles selected, 4 studies examined serum levels of vitamin D in affected individuals (17,18,21,22), 2 studies studied the effect of vitamin D supplementation on OLP symptoms (23,24), in 2 studies, the association of VDR gene polymorphisms and OLP risk have been investigated (25,26) and 6 studies have investigated the mechanisms of OLP formation due to vitamin D deficiency (27–32) (Table 1).