What is Vitamin A?

Vitamin A is a fat soluble vitamin that is required for a number of bodily functions. This vitamin is needed to maintain good vision and a healthy immune system, as well as being essential for growth and development.

Vitamin A describes a group of compounds that include retinol, retinoic acid, retinal, and a number of provitamin A carotenoids such as beta-carotene. All types of vitamin A contain a beta-ionone ring with an isoprenoid chain attached which is referred to as the retinyl group. Both structures are required for vitamin activity.

Functions of Vitamin A

In the eyes, retinal is combined with a protein called opsin to give rhodopsin, an essential light absorbing molecule needed for color vision and seeing in dim light.

Another form of Vitamin A, retinoic acid, is a key hormone-like growth factor for epithelial cells and other cell types in the body.

Sources of Vitamin A

Vitamin A is found in both plant and animal food sources. The form of vitamin A absorbed when animal sources are consumed is retinyl palmitate, which gets converted into an alcohol called retinol. Retinol acts as a storage form of vitamin A, which can be converted to and from retinal, the active aldehyde form of the molecule. One of the richest animal sources of Vitamin A is liver.

Plant sources of Vitamin A include orange and yellow fruits and vegetables such as carrots, pumpkin, sweet potato, apricots and mangoes. The orange/yellow pigment occurs due to the presence of provitamin A carotenoids such as beta-carotene. These compounds need to be converted into vitamin A or retinol in the body before they can be used.

The daily amount of vitamin A required by adults is 0.7 mg for men and 0.6 mg for women. Any vitamin A that is not required immediately is stored for future use in bodily functions.

Sources

  1. http://www.nhs.uk/Conditions/vitamins-minerals/Pages/Vitamin-A.aspx
  2. http://www2.moh.gov.my/images/gallery/rni/11_chat.pdf
  3. http://ocw.jhsph.edu/courses/InternationalNutrition/PDFs/Lecture3.pdf
  4. http://www.who.int/publications/cra/chapters/volume1/0211-0256.pdf
  5. http://www.unicef.org/publications/files/Vitamin_A_Supplementation.pdf

Further Reading

Last Updated: Aug 23, 2018

Ananya Mandal

Written by

Ananya Mandal

Ananya is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.

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