New knowledge of the biological and clinical importance of the steroid hormone 1alpha, 25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and its receptor, the vitamin D receptor (VDR), has resulted in significant contributions to good bone health.
[Note: To view an illustration of the complex vitamin D receptor, visit Professor Norman’s website http://www.biochemistry.ucr.edu/faculty/norman.html]
However, worldwide reports have highlighted a variety of vitamin D insufficiency and deficiency diseases. Despite many publications and scientific meetings reporting advances in vitamin D science, a disturbing realization is growing that the newer scientific and clinical knowledge is not being translated into better human health.
Over the past several decades, the biological sphere of influence of vitamin D3, as defined by the tissue distribution of the VDR, has broadened at least 9-fold from the target organs required for calcium homeostasis (intestine, bone, kidney, and parathyroid). Now, research has shown that the pluripotent steroid hormone 1alpha,25(OH)2D3 initiates the physiologic responses of 36 or more cell types that possess the VDR.
In addition to the kidney's endocrine production of circulating 1alpha,25(OH)2D3, researchers have found a paracrine production of this steroid hormone in 10 or more extrarenal organs.
This article identifies the fundamentals of the vitamin D endocrine system, including its potential for contributions to good health in 5 physiologic arenas in which investigators have clearly documented new biological actions of 1alpha,25(OH)2D3 through the VDR.
As a consequence, the nutritional guidelines for vitamin D3 intake (defined by serum hydroxyvitamin D3 concentrations) should be reevaluated, taking into account the contributions to good health that all 36 VDR target organs can provide.
Source: American Journal of Clinical Nutrition, Aug 2008. 88(2), 491S-499S. PMID: 18689389, by Norman, AW. Department of Biochemistry and Division of Biomedical Sciences, University of California, Riverside, California, USA. [E-mail: email@example.com]