The effects of vitamin D have been known since before the twentieth century. Vitamin D3, also known as cholecalciferol, shows antirachitic activity (1, 2). Rickets is a childhood disease that is a result of vitamin D deficiency (1). In 1925, it was established that natural oils contain vitamin D3 (3, 4). Vitamin D3 differs from the typical definition of a vitamin. It is classified as a prohormone because it must be activated before it can be used by the body (4). Also it is one of the few substances that is classified as both exogenous and endogenous because it can be ingested in the diet or made entirely in the body (5).
Vitamin D3 (C27H44O)
There are two basic methods for the synthesis of vitamin D3. One method requires UV radiation and another does not. It was discovered in the 1920s that vitamin D3 is converted to its active form upon UV radiation (2). The starting material is a cholesterol derivative, whose structure was first synthesized in the 1950s (Scheme 1). The initial compound is easily converted to 7-dehydrocholesterol (Scheme 1). Woodward (2, 6) developed a system in 1952 to synthesize the cholesterol derivative. His 20-step reaction synthesis starts with a molecule to produce the cholesterol derivative shown in Scheme 1. Robinson and colleagues (2, 6) developed a different synthesis of the starting material in 1953. His synthesis began with a different molecule and also yields the cholesterol derivative. Lythgoe (2) accomplished the first pure chemical synthesis of 7-dehydrocholesterol in 1967. The development of the cholesterol derivative without photochemical radiation is still being investigated in order to study the metabolism of the vitamin (2).
Upon exposure to the sun, 7-decholesterol is activated. After about a week, 7-decholesterol is removed from the skin by the protein that binds vitamin D (binding protein) (2). The binding protein binds 7-decholesterol easily. It functions to transport the lipophilic steroid through the hydrophilic blood plasma (2, 3). The carrier is free in the blood, but its function in the blood stream is unclear (3). Vitamin D3 undergoes a reaction in the liver. Parathyroid hormone is released when blood calcium levels are low to stimulate an enzyme in the kidneys, which increases production of the product that is excreted in the urine (2).
Future of Vitamin D3
The demand for fat-free food is increasing every day. With this demand comes a decrease in vitamin D intake since it is found mainly in fat substances. The vitamin needs a fat-free delivery system. Li et al. (4) experimented with an amphiphilic molecule as a biological delivery system. This molecule forms a micelle with a lipophilic core to transport vitamin D through the body. This is still being studied because the amphiphilic molecule is synthesized using toxic methods and is therefore not biologically safe (4).
(1) Wagner, A. F; Folkers, K. The Vitamin D Group. Vitamins and Coenzymes, Interscience Publishers: New York, 1964; pp 330-331.
(2) Collins, E.D.; Norman, A. W. Vitamin D. In Handbook of Vitamins, 2nd ed; Machlin L. J, Ed.; Marcel Dekker: New York, 1990; pp 60-61,67-73.
(3) Camille, E.P.; Ricciardi, C.; Berg, A. B.; Erdensanna, D.; Collerone, G.; Ankers, E.; Wenger, J.; Karumanchi, S. A.; Thadhani, R.; Bhan, I. Vitamin D-Binding Protein Modifies the Vitamin D-Bone Mineral Density Relationship. J. Bone Miner. Res. 2011, 26, 1609-1616. <http://onlinelibrary.wiley.com/doi/10.1002/jbmr.387/abstract;jsessionid=6197E6DFDCE1566508E0F761469B1A04.d02t02>
(4) Li, Q.; Lui, C.; Huang, Z.; Xue, F. Preparation and Characterization of Nanoparticles Based on Hydrophopic Alginate Derivative as Carriers for Sustained Release of Vitamin D3. J. Agric. Food Chem. 2011, 59, 1962-1967. <http://pubs.acs.org/doi/abs/10.1021/jf1020347>
(5) Williams, R. J. The Functioning of Vitamins and Hormones. J. Chem. Educ. 1959, 36, 538-540. <http://pubs.acs.org/doi/abs/10.1021/ed036p538>
(6) Norman, A. W. Metabolism of Vitamin D. Vitamin D: The Calcium Homeostatic Steroid Hormone, Academic Press: New York, New York, 1979, pp 59-60,186-189.