Enviromental endotoxin is downregulating the vitamin D receptor and (probably) also vitamin sensitivity in Zhao et al.
The suppressive function of vitamin D on oral lichen planus (OLP) have been documented previously. Vitamin D receptor (VDR) expression is down-regulated in OLP, but the molecular mechanism of its decrease and the related anti-in ammatory contributor of epithelial VDR signaling is unclear. Herein, we demonstrated that lipopolysaccharide (LPS) remarkedly down-regulated VDR expression of keratinocytes, and the reduced regulation was dependent on tumor necrosis factor alpha (TNFα)- miR-346 pathway.
This is a good but never tested explanation of the lower allergy rate in Alpine farmers where high endotoxin prevents from sensitizing effects of vitamin D supplementation of newborns. The only in vivo study so far is a retrospective analysis of vitamin D serum levels in adults, where the combination of high endotoxin and low vitamin D was associated with current asthma. Maybe supplementation of newborns and serum levels in adults is a completely different thing at least I think it is worthwhile to examine VDR in tissue homogenates, cell lysates or other biological fluids derived from active farmers.