It is a fat-soluble vitamin and it is also well famous as Retinol .

In 1912 Hopkins reported usual and continued development when whole milk was added to purified supplies in young rats, and this study led up to the discovery of this vitamin by McCollum. In 1915 McCollum and Davis well-known the vital factors in eggs, butter and milk, i.e. 'fat soluble A' in eggs and butter, and water soluble B in milk. 'Fat soluble A' cured Xerophthalamia.

Vitamin A is made up of three kind of molecules, retinal, retinal and retinoic acid. Each of these is access from the plant precursor molecule, b- carotene.

Food sources of vitamin A

Vitamin A is extensively circulated in animal and plant foods- in animal foods as preformed vitamin A (retinol), and in plant foods as provitamins (carotenes).

* Animal foods: Foods rich in retinol are liver, eggs, butter, cheese, milk, fish and meat. Fish liver oils are the richest natural sources of retinal, but they are usually used as nutritional supplements slightly than as food sources.

* Plant foods: The cheapest source of vitamin A is green leafy vegetables such as spinach and amaranth, which are create in huge abundance in nature throughout the year. The darker the green leaves the superior the carotene content. Vitamin A mostly founds in green and yellow fruits and vegetables (e.g. papaya, mango, pumpkin) and in some roots (e.g. carrots). The most vital carotenoid is beta-carotene, which has the uppermost vitamin A. carotenes, is converted to vitamin A in small intestine. Vegetable sources of beta-carotene are free of fat and cholesterol.

Vitamin A content of some foods is given below in the table

Functions of vitamin A

Vitamin A is necessary for development. Vitamin a helps in the normal development of bones and teeth, mainly in children and young people. It is a part of rhodopsin, hence necessary for night vision. Vitamin A is the "beauty vitamin". It helps to stay the skin smooth and soft. It is also required for the mucous membranes lining the nose, throat, and bronchial tubes, as well as the whole digestive tract, the bladder, kidneys, and pelvic organs. Prevents infection. It also plays vital part in protein synthesis. It controls the action of the bone cells, so that normal development and shape of bone are maintained. It also helps in keeping the normal fertility. It prevents a situation known as urolithiasis where urinary calculus in the form of calcium phosphate is present. Vitamin A also controls the integrity of the epithelial tissues. A moist surface is maintained and this helps to prevent next to hyperplasia, metaplasia and keratinization.

It is believed that free radicals are connected with a lot of degenerative changes with aging. However, it is yet been established. For example, on study it is found that in smokers who took high doses of beta-carotene has increased threat of cancers. With vitamin A, as with a lot of other vitamins, a certain amount is required, but too much is dangerous for the health.

Synthesis: In the body it is synthesized by carotene. One molecule of beta carotene create two molecule of vitamin A. hence carotene is known as provitamin A. in man the liver is believed to be the only organ which performs this adaptation.

Daily requirement:

The daily requirement of vitamin A in adults is 5000 IU for men and 4000 IU in women

For growing children and period of puberty, lactation and pregnancy 6000-8000 IU. Foods fortified with vitamin A such as cereals, juices, dairy products can be significant sources of vitamin A.

Deficiency symptoms of vitamin A

Be short of of vitamin a cause's night blindness or inability to see in the dim light. The mother herself can notice this circumstance when her child cannot see in the late evenings or find her in a darkened room. Conjunctival xerosis is a clinical sign created by the deficiency of vitamin A. The conjunctivas become waterless and non-wettable. In its place of looking smooth and shiny, it appears muddy and wrinkled. When vitamin A is absent the skin becomes thick and rough. A virus appears in various parts of the body. Kidney and bladder stones are more ordinary in people whose diets are deficient in vitamin A. deficiency of vitamin A also outcome in the abnormal bone development in certain parts of vertebral column and skull. It is believed that effects on nervous system are partly due to abnormal type of development giving pressure effect on nerves. Deficiency also interferes with the usual procedure of ovulation although it is not proved in man. Deficiency of vitamin A also raises the threat of cancer. The deficiency also causes defective enamel creation of the teeth and pyorrhea alveolaris.

Vitamin A deficiency

They consist of night blindness, conjunctival xerosis, Bitot's spot, corneal xerosis and keratomalacia

Over dosage signs of vitamin A

Large doses of vitamin A causes drowsiness, sluggishness, severe headache, vomiting, peeling of skin, hair loss, fatigue, ulcerations in the eyes, spontaneous fracture and haemorrhages. The haemorrhagic manifestations connected with hypervitaminosis may be prevented by concurrent administration of vitamin K. The antioxidant action of tocopherols is almost certainly responsible for its sparing action on vitamin A and carotene. This protecting effect of vitamin E is improved by other antioxidants such as ascorbic acid, etc.

How to store the vitamin A

Heat and moisture may alter the vitamin. Refrigeration is advised.