SubscribeVitamin D is a commonly used collective term for a family of closely related seco-steroids. Vitamin D is metabolised by a hepatic 25-hydroxylase into 25-hydroxyvitamin D (25(OH)D; calcidiol), and by a renal 1α-hydroxylase into 1,25-dihydroxyvitamin D (1,25(OH)2D; calcitriol).
1,25(OH)2D receptors are present in many different tissues, and apart from the kidney, a wide variety of both normal and cancer tissues and cells also possess the enzyme 1-hydroxylase, which is able to use circulating 25(OH)D as a substrate.
The serum concentration of 25(OH)D is considered to be the most reliable measure of overall vitamin D status and can be used to determine whether a patient is vitamin D sufficient.
The present article provides an overview of vitamin D structure, metabolism and function. It also outlines the causes of vitamin D deficiency, and the definition of vitamin D status, and provides evidence for the involvement of low vitamin D levels in the pathogenesis of chronic diseases.