Vitamin D and Atopy.

Theoharis C. Theoharides, MS, MPhil, PhD, MD, FAAAAI Vitamin D is primarily found in vertebrates and it is mostly responsible for calcium homeostasis and maintenance of healthy bones. Natural vitamin D is obtained from intake of fish oils and other animal sources. Interestingly, microalgae contain both pre vitamin D and active vitamin D3. In humans, vitamin D synthesis is initiated in the skin by a photochemical conversion of pre vitamin D3 by ultraviolet B rays, followed by isomerization to vitamin D3 (cholecalciferol). Vitamin D then undergoes the first hydroxylation in the liver to 25-hydroxyvitamin D3 [25(OH)D3], the circulating metabolite, which is what is meant when the term vitamin D is used in this Editorial. The active form of vitamin D is 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] (calcitriol) and is synthesized primarily in the kidneys. 1