Vitamin D Basics

Hormone Functions

The vitamin D hormones have essential roles in human health. Vitamin D hormones act by binding to and activating the vitamin D receptor (VDR) to regulate the expression of genes in a tissue-specific manner.  Vitamin D hormones regulate blood calcium levels by controlling intestinal absorption of dietary calcium and reabsorption of calcium by the kidneys. Concomitantly, vitamin D hormones suppress the production of the calcium regulating hormone, parathyroid hormone (PTH), by the parathyroid glands.

The vitamin D hormones also participate in the regulation of cellular differentiation and growth, as well as bone formation and metabolism. Additionally, vitamin D hormones are required for the normal functioning of the musculoskeletal, immune and renin-angiotensin systems. There is a growing body of evidence linking vitamin D insufficiency with cognitive and neural dysfunction. The widespread beneficial effects of vitamin D hormones are continually being elucidated through studies directed to the intracellular VDR and the corresponding networks of VDR-responsive genes in nearly every human tissue. It is becoming evident that vitamin D insufficiency has a widespread and significant impact on a number of key physiological systems.