chronic inflammatory disease: a low 25-D and a high 1,25-D.

[Jean]

A number of studies have suggested that patients with chronic inflammatory diseases are deficient in 25-hydroxyvitamin-D (25-D) and that consuming greater quantities of vitamin D, which further elevates 25-D levels, alleviates symptoms of disease. Some years ago, molecular biology identified 25-D as a secosteroid. Secosteroids would typically be expected to depress inflammation, which is in line with the reports of symptomatic improvement. The simplistic first-order mass-action model used to guide the early vitamin studies has given way to a more complex description of action. When active, the Vitamin D nuclear receptor (VDR) affects transcription of at least 913 genes and impacts processes ranging from calcium metabolism to expression of key antimicrobial peptides.

Located in the nucleus of a variety of cells including immune cells, the VDR is a control system of sorts. When exposed to infection and damage, especially that which is caused by pathogens, the body begins to convert the inactive form 25-D into the active form, 1,25-D. As cellular concentrations of 1,25-D increase, 1,25-D activates the VDR, turning on any number of tens of thousands of genes the receptor transcribes. The activation of certain genes leads to the synthesis of antimicrobial peptides. The antimicrobial peptides are the body’s “natural antibiotics” and have a potent anti-bacterial effect.

However, bacteria create ligands, which like 25-D, inactivate the VDR and, in turn, the innate immune response. This allows the microbes to proliferate. In response, the body increases production of 1,25-D from 25-D, leading to one of the hallmarks of chronic inflammatory disease: a low 25-D and a high 1,25-D.

This pattern is a result of the disease process rather than a cause. For a variety of reasons, neither increased consumption of vitamin D nor the body’s synthesis of additional 1,25-D is ultimately effective at combatting infection.

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