"There is a critical vitamin D receptor (VDR) in the intestinal lining. The second issue regarding Vitamin D beyond our typical deficiency involves VDR. If the intestinal lining is injured (vit D receptors are in the microvilla) the loss of Vit D receptors affects the entire body. The study below shows the relationship between intestinal bacteria and the VDR receptor."
Vitamin D and Gut Flora | Dr Thomas's Blog