Benders'dictionary of nutrition and food technology

501VITAMIN Dintakes are 10–15µg/day for adults, amounts that are unlikely tobe obtained from unsupplemented diets.The obsolete international unit of vitamin D = 25 ng calciol;1mg calciol = 40 IU.vitamin D resistant rickets See rickets.vitamin D toxicity Excessive intake of vitamin D results in disturbanceof calcium metabolism, resulting in hypercalcaemia,dangerously raised blood calcium concentrations, leading toraised blood pressure, and calcinosis, inappropriate depositionof calcium in soft tissues, leading to brain and kidney damage.Excessive exposure to sunlight does not lead to excessive formationof vitamin D because previtamin D undergoes furtherlight-catalysed reactions to inactive compounds, and there is onlylimited availability of 7-dehydrocholesterol in the skin.vitamin E (see p. 502) Two main groups of compounds havevitamin E activity: the tocopherols and the tocotrienols; there arefour isomers of each: α-, β-, γ- and δ-tocopherols and α-, β-, γ-and δ-tocotrienols, with differing potencies.Deficiency symptoms vary considerably in different animalspecies; sterility in mouse, rat, rabbit, sheep and turkey; musculardystrophy in several species; capillary permeability in chickand turkey; anaemia in monkey. Human dietary deficiency isunknown, but hereditary lack of β-lipoprotein leads to functionaldeficiency, with severe neurological damage. Premature infantsmay show haemolytic anaemia as a result of vitamin E deficiency.Functions as an antioxidant in cell membranes, protectingunsaturated fatty acids from oxidative damage. It also hasmembrane-specific functions, and a role in cell signalling andmodulation of gene expression.The vitamin E content of foods is expressed as milligrams α-tocopherol equivalent (based on the different potency of the differentvitamers). The obsolete international unit of vitamin E