Vitamin A is a nutritional organic compound which includes retinal, retinoic acid, retinol, beta-carotene and carotenoids. Vitamin A plays a major role in growth and development along with maintenance of vision and good immune system. Retina of the eye requires vitamin A to form retinal which in combination with protein opsin forms rhodopsin which functions as the light-absorbing molecule. Vitamin A also functions as retinoic acid which is a hormone like growth factor for cells. All vitamin A forms have a beta-ionone ring which contains an isoprenoid chain attached to it which is known as the retinyl group. Vitamin activity requires both the structural features. Retinol is absorbed when animal food sources are consumed. They are yellow and fat soluble.

Vitamin A plays a big role in various body functions which includes vision, immune functioning, antioxidant activity, bone metabolism, skin and cellular health, embryonic development and reproduction and gene transcription. Deficiency of vitamin A can affect children and also prove to be detrimental. Deficiency can be either characterized as primary or secondary. Primary deficiency includes individuals who do not consume sufficient provitamin A carotenoids in their diet, whereas secondary vitamin A deficiency is due to chronic malabsorption of lipids, chronic exposure to oxidants or due to impaired production and release of bile. Vitamin A deficiency leads to impaired vision as it functions as a visual chromophore. Persistent deficiencies lead to conditions called xerophthalmia. Excessive consumption of vitamin A can cause anorexia, nausea, vomiting, hair loss, headaches, abdominal pain, weakness and altered mental status. Some of these symptoms are common when isotretinoin is used for acne treatment. The symptoms get resolved once the intake of vitamin A is stopped. Significant effects of vitamin A is shown on foetuses during organogenesis.