Vitamin A refers to a group of chemicals that are all able to provide the same function in humans. Retinal, retinol, retinaldehyde, retinoic acid and β-carotene (and certain other carotenoids) can all provide the activity of vitamin A. Vitamin A is essential to growth and development and a deficiency of vitamin A causes metabolic dysfunction and death. However, vitamin A is a teratogenic chemical in that high intakes of retinal, retinol, retinaldehyde and retinoic acid can cause abnormalities in foetal growth. However, β-carotene does not have this effect. Therefore women who are pregnant or are likely to get pregnant are advised to limit vitamin A intake to no more than the recommended intake. If supplements are required it is recommended that β-carotene is used for this purpose. Generally foods that are very high in vitamin A are the livers of animals and fish, and this includes cod liver oil. Multivitamins have been formulated for pregnant women that contain no vitamin A, but instead provide β-carotene.
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