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see Vitamin A under vitaminvitamin,
group of organic substances that are required in the diet of humans and animals for normal growth, maintenance of life, and normal reproduction. Vitamins act as catalysts; very often either the vitamins themselves are coenzymes, or they form integral parts of coenzymes.
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(also called axerophthol or vitamin A), an isoprenoid whose chemical formula is C20H30O. Retinol is soluble in nonpolar organic solvents, insoluble in water, and has a melting point of 63°–64°C. In animals and man, it is converted from the carotene in food and stored mainly in the liver; it is particularly abundant in the liver of whales and fish and in fish oil.

The most important biological function of retinol is its participation in the form of retinal in the visual process. A retinol deficiency results in impairment of twilight vision (night blindness, or nyctalopia) and in injury to epithelial tissue, as in xe-rophthalmia. An excess of retinol causes a variety of metabolic disturbances, an accumulation of retinol in the hydrophobic fraction of cell membranes, and destruction of these membranes. Retinol is commercially synthesized from β-ionone. Retinol is sometimes called vitamin A1; its dehydro derivative C20H28O is called vitamin A2. Retinal1 and retinal2 are distinguished accordingly.


References in periodicals archive ?
Prevalence of vitamin A deficiency was defined as low serum retinol concentrations (< 0.
20) For the prevalence of vitamin A deficiency among pregnant women, a uniform probability distribution was specified, with a minimum of 1% and a maximum of 6% (yielding a midpoint estimate of about 3.
The prevalence of vitamin A deficiency in South African children aged 0-4 years was estimated at 33.
The population-attributable fractions (PAFs) for the selected health outcomes as well as the estimated number of cause-specific deaths and DALYs attributed to vitamin A deficiency among children aged 0-4 years are shown in Table II.
8% of all healthy years of life lost (YLLs) in South Africa in 2000) were associated with vitamin A deficiency (Table III).
Vitamin A deficiency is a public health problem among preschool children in South Africa, with 33.
Vitamin A deficiency accounted for 3 069 deaths in children aged 0-4 years (3.