IJCS | Volume 31, Nº4, July / August 2018

423 Jorge et al. Vitamin D and cardiovascular disease Int J Cardiovasc Sci. 2018;31(4)422-432 Review Article Table 1 - Some food sources of vitamin D. Adapted from the Brazilian Society of Endocrinology and Metabolism 11 Food Portion Amount of vitamin D per portion Wild salmon 100 g 600 – 1,000 IU of vitamin D 3 Farmed-raised salmon 100 g 100 – 250 IU of vitamin D 3 Canned sardines 100 g 300 IU of vitamin D 3 Canned mackerel 100 g 250 IU of vitamin D 3 Canned tuna 100 g 230 IU of vitamin D 3 Cod liver oil 5 mL 400 – 1,000 IU of vitamin D 3 Egg yolk 1 unit 20 IU of vitamin D 3 Fresh mushrooms 100 g 100 IU of vitamin D 2 Sun-dried mushrooms 100 g 1,600 IU of vitamin D 2 methyl group on carbon 24, as shown in Figure 2. Both vitamins are synthesized from energy derived by photolysis (solar radiation) on their precursors: ergosterol (vitamin D2) and 7-DHC (vitamin D3). Following ingestion by humans, both vitamins follow the same metabolization pathway in the liver and are converted into 25-hydroxyvitamin D. 11 Synthesis of endogenous vitamin D starts in the deep layers of the epidermis, where the precursor 7-DHC is stored in the double lipid layer of the cell membrane. Ultraviolet B (UVB) radiation promotes 7-DHC photolysis, leading to the formation of a secosteroid molecule: previtamin D3. This molecule is thermally unstable and undergoes an isomerization reaction induced by heat, converting it into vitamin D3. Skin melanin competes for the radiation photon, decreasing the availability of photons for 7-DHC photolysis, hence the observation of lower vitamin D levels in blacks. 11 When reaching the liver, vitamins D2 and D3 undergo hydroxylation by cytochrome P450 and originate 25-hydroxyvitamin D, which is the form of the vitamin that predominates in the circulation. In the blood, about 85 to 90%of the 25-hydroxyvitaminD is bound to vitamin The molecular structure of vitamins D2 and D3 is very similar. Ergocalciferol differs from cholecalciferol by a double bond between carbons 22 and 23 and a Figure 1 - Global prevalence of vitamin D deficiency in adults. Adapted from: Palacios C, Gonzalez L. Is vitamin D deficiency a major global public health problem? J Steroid Biochem Mol Biol. 2014 October; 144PA: 138–145. doi:10.1016/j.jsbmb.2013.11.003. USA CHILE SPAIN SWITZERLAND FINLAND GERMANY AFRICA AUSTRALIA INDIA Vitamin D levels < 12 ng/mL < 20 ng/mL BRAZIL