Vitamin A is a fat-soluble nutrient essential for human health.
Vitamin A is found in two different forms:
Preformed vitamin A is directly available by the body and is mainly found in animal sources. It is composed of retinol, retinal and retinoic acid.
Provitamin A is not directly available and need to be converted into the active form of vitamin A by our small intestine. It is mainly found in plants and is composed of alpha-carotene, beta-carotene and beta-cryptoxanthin.
To take into account the differences in bioavailability of these compounds, the FNB (Food and Nutrition Board of the Institute of Medicine) suggest vitamin A should be expressed in terms of Retinol Activity Equivalents (RAE).
Vitamin A contributes to many bodily functions, including:
Vitamin A is critical for vision because it is a component of a protein called rhodopsin that absorbs light in the eye.
Vitamin A is involved in the production of white blood cells that are part of your body’s natural defence against infection (1).
Vitamin A keeps your skin and the mucous in your eyes, lungs, gut, and nose healthy. This helps trap bacteria and other pathogens.
Recommended Daily Allowance for a 44-year-old male moderately active, weighting 70 kg and 175 cm tall is 900 RAE and the Tolerable Upper Intake is 3 000 RAE (2).
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Vitamin A deficiency may cause the following:
Because vitamin A is fat soluble, the body stores excess amounts, primarily in the liver, and these levels can accumulate.
Excess preformed vitamin A can be toxic or even fatal however excess of provitamin A carotenoids does not seems to cause major adverse effects (3).
Excess preformed vitamin A can cause: