Vitamin D3, or cholecalciferol, is the most bioavailable form of vitamin D. It is usually extracted from fish, cod and sardine oils. Butter and egg yolk are also good sources of vitamin D. Vegetables are generally low in vitamin D, with green leafy vegetables being the richest. Vitamin D can also be produced through the action of Ultraviolet rays on the lanolin present in sheep's wool. Vitamin D3 supplements usually also contain vitamin A in their composition and, therefore, in cases of need for vitamin A restriction, as for example in pregnancy, the intake of Vitamin D will be consequently affected. This product does not contain vitamin A. The knowledge that we must protect ourselves from sunburn and the effects of ultraviolet rays on our skin, resulted in a greater use of sunscreens, hats and clothing in order to protect ourselves from the sun, which in turn reduced the production of vitamin D by the skin. The deficiency of this vitamin has become more common in general, with the elderly standing out because they are usually less exposed to sunlight. Vitamin D is unique among the essential nutrients as it is a vitamin that has the ability to transform into a hormone. Once ingested, and already in the liver, vitamin D is converted into a metabolite called 25-hydroxycholecalciferol [25-OH-D3], which in turn will be converted into its active form in the kidneys, into 1,25 dihydroxycholecalciferol [1 ,25-(OH)2-D3]. It is in this active form that Vitamin D acts as a hormone, 10 times more powerful than its precursor, and like other hormones, it functions as a chemical messenger responsible for regulating certain functions in the body. Traditionally, vitamin D is associated with calcium balance and bone health. It favors the assimilation of calcium and phosphorus necessary for healthy bones and teeth. Since it is produced in the kidneys, the active form of Vitamin D acts in different processes: mobilization of calcium and phosphorus into the bone tissue, it is vital for the absorption of calcium and phosphorus ingested through food and the reabsorption of calcium in the kidneys, acting on the thyroid and parathyroid, as well as playing a role in nervous and immune function.
