This article appeared in the Summer 2008 edition of Celiac.com's Scott-Free Newsletter.

Celiac.com 06/16/2008 - Do vitamin D deficiency, gut bacteria, and timing of gluten introduction during infancy all combine to initiate the onset of celiac disease? Two recent papers raise the potential that this indeed may be the case. One paper finds that when transgenic mice expressing the human DQ8 heterodimer (a mouse model of celiac disease) are mucosally immunized with gluten co-administered with Lactobacillus casei bacteria, the mice exhibit an enhanced and increased immune response to gluten compared to the administration of gluten alone.[1] A second paper finds that vitamin D receptors expressed by intestinal epithelial cells are involved in the suppression of bacteria-induced intestinal inflammation in a study which involved use of germ-free mice and knockout mice lacking vitamin D receptors exposed to both friendly and pathogenic strains of gut bacteria.[2] Pathogenic bacteria caused increased expression of vitamin D receptors in epithelial cells. Friendly bacteria did not.

If one considers these two papers together, one notices: (1) Certain species of gut bacteria may work in conjunction with gluten to cause an increased immune response which initiates celiac disease; (2) The presence of an adequate level of vitamin D may suppress the immune response to those same gut bacteria in such a way as to reduce or eliminate the enhanced immune response to gluten caused by those gut bacteria, thus preventing the onset of celiac disease.

Vitamin D has recently been demonstrated to play a role in preserving the intestinal mucosal barrier. A Swedish study found children born in the summer, likely introduced to gluten during winter months with minimal sunlight, have a higher incidence of celiac disease strongly suggesting a relationship to vitamin D deficiency.[3] Recent studies found vitamin D supplementation in infancy and living in world regions with high ultraviolet B irradiance both result in a lower incidence of type 1 diabetes, an autoimmune disease closely linked to celiac disease.[4][5]

Gut bacteria have long been suspected as having some role in the pathogenesis of celiac disease. In 2004, a study found rod-shaped bacteria attached to the small intestinal epithelium of some untreated and treated children with celiac disease, but not to the epithelium of healthy controls.[6][7] Prior to that, a paper published on Celiac.com[8] first proposed that celiac disease might be initiated by a T cell immune response to "undigested" gluten