However, VD does not remain in circulation for a long time as it is almost instantly stored on the adipose tissue or metabolized in the liver. Once produced, VD is translocated into the bloodstream. In the epidermis, VD is produced in the form of cholecalciferol due to the action of sunlight. VD is a precursor to its active and biologically functional metabolite, a lipophilic seco-steroid hormone known as calcitriol. Vitamin D (VD) was firstly identified as a vitamin and now is recognized as a prohormone. In this chapter, an overview on vitamin D and its metabolic activity is presented, as well as a review of nanosystems for the encapsulation of vitamin D for different applications, such as food and pharmaceutical industries. Thus, the use of nanotechnology may overcome these problems associated with vitamin D administration, allowing to decrease its toxicity in healthy tissues and increasing its bioavailability. However, its administration presents some drawbacks such as high toxicity and low bioavailability. Also nowadays, vitamin D is recognized as a potential therapeutic agent in anticancer therapy. Thus, the awareness that vitamin D insufficiency/deficiency may be associated with various diseases has grown. In addition to the traditional role of calcium homeostasis and bone mineralization, calcitriol, the active metabolite of vitamin D, also displays other metabolic activities as antiproliferative, pro-differentiating, anti-inflammatory, immunomodulatory, and antineoplastic effects.

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