Vitamin D: The Introduction

Introduction to Vitamin D - Part I

When I was in medical school, not so very long ago, the understanding of vitamin D was basically that it played a role in regulating calcium metabolism and hence bone health and that was about it. However, we have come to realize very recently that vitamin D is a pleiotrophic regulator, involving itself in the proper function of many bodily systems involved in health. Vitamin D's relation to the immune system, as we now understand it, would have read more like something from a science fiction book than a medical textbook just a few short years ago.

A significant component of the immune system was, until recently, not merely not well understood, it was entirely undiscovered. About ten years ago or so researchers began to become aware of a variety of endogenous small molecules that came to be known as antimicrobial peptides (AMPs). As the name implies, these molecules were found to attack invading bacteria although some of them are now known to attack viruses as well. They attack the invading pathogens through a variety of different mechanisms such as punching a hole in the cell membrane or binding to and interfering with molecules inside the invading bacteria. There are now whole different classes of AMPs that have been described, each class in turn has many individual AMP molecules, there are now over 1200 unique AMPs which have been identified. For those interested in reading further on AMPs, a March 2009 article from the journal Trends in Immunology (see ref 1 below gives an excellent overview of the current state of knowledge.

Our understanding of AMPs is very far from complete and it remains an area of intense research. In addition to fighting off invading pathogens it also appears that AMPs have a role in modulating the broader immune response itself. One of the more fascinating aspects to all this is that it has also only recently became apparent that vitamin D is an important regulator of AMP expression. So, far from simply preventing rickets and regulating calcium metabolism, it is the consensus medical research opinion, supported by a large number of studies that vitamin D plays an important role in immune regulation.

However, even this is not the end of the story for what we are now learning about this fascinating molecule. A recent article (see ref 2 below) from Bioessays summarizes the multiple potential effects of vitamin D,

"Molecular genetic techniques including genomics have helped reveal that 1alpha,25-dihydroxyvitamin D3 can control more than calcium homeostasis. It has widespread effects on cellular differentiation and proliferation, and can modulate immune responsiveness, and central nervous system function. Moreover, accumulating epidemiological and molecular evidence suggests that 1alpha,25-dihydroxyvitamin D3 acts as a chemopreventive agent against several malignancies including cancers of the prostate and colon."

By Paul D Maher