Known as anti-opathalmic, vitamin A is essential for growth and vitality. It builds up resistance to respiratory and other infections and works mainly on the eyes, lungs, stomach and intestines. It prevents eye diseases and plays a vital role in nourishing the skin and hair. It helps to prevent premature ageing and senillity, increases life expectancy and extends youthfulness. The main sources of this vitamin are fish liver oil, liver, whole milk, curds, pure ghee, butter, cheese, cream and egg yolk, green leafy and certain yellow root vegetables such as spinach, lettuce, turnip, beets, carrot, cabbage and tomato and ripe fruits such as prunes, mangoes,pappaya, apricots, peaches, almonds and other dry fruits. A prolonged deficinecy of vitamin A may result in inflammation of the eyes, poor vision frequent colds, night blindness and increased susceptibility to infections, lack of appetite and vigour, defective teeth and gums and skin disorders.

The recommended daily allowance of vitamin A is 5,000 international units for adults and 2,600 to 4,000 international units for children. When taken in large therapeutic doses, which are usually 25,000 to 50,000 units a day, it is highly beneficial in the treatment of head and chest colds, sinus trouble, influenza and other infectious diseases . It is also valuable in curing night blindness and other eye diseases as well as many stubborn skin disorders. This vitamin can be given upto 1,00,000 units a day for a limited period of four weeks under doctor's supervision.

Vitamin A and carotene can be obtained from either animal or vegetable sources. The animal form is divided between retinol and dehydroretinol whereas the vegetable carotene can be split into four very potent groups - alpha-carotene, beta-carotene, gamma-carotene and crypto-carotene. With enough beta-carotene available in the body, the body can manufacture its own vitamin A.

Vitamin A is required for

Vitamin A is required for night vision, and for a healthy skin. It assists the immune system, and because of its antioxidant properties is great to protect against pollution and cancer formation and other diseases. It also assists your sense of taste as well as helping the digestive and urinary tract and many believe that it helps slow aging.
It is required for development and maintenance of the epithelial cells, in the mucus membranes, and your skin, and is important in the formation of bone and teeth, storage of fat and the synthesis of protein and glycogen.

Deficiency of vitamin A

A deficiency of vitamin A may lead to eye problems with dryness of the conjunctiva and cornea, dry skin and hair, night blindness as well as poor growth. Dry itchy eyes that tire easily are normally a warning of too little vitamin A. If the deficiency become severe, the cornea can ulcerate and permanent blindness can follow.
Abscesses forming in the ear, sinusitis, frequent cold and respiratory infections as well as skin disorders, such as acne, boils and a bumpy skin, as well as weight loss might be indicative of the vitamin being in short supply. Insomnia, fatigue and reproductive difficulties may also be indicative of the vitamin in short supply. Your hair and scalp can also become dry with a deficiency, especially if protein is also lacking.

Dosage

The dosage underneath is the Recommended Dietary Allowance (RDA), but be aware that this dosage is the minimum that you require per day, to ward off serious deficiency of this particular nutrient. In the therapeutic use of this nutrient, the dosage is usually increased considerably, but the toxicity level must be kept in mind.
Male 5,000 IU per day (1,000 µg equivalent), female 4,000 IU per day (800 µg retinol equivalent), although 10,000 IU per day is normally used in supplementation.

Toxicity and symptoms of high intake

Dosages exceeding 15,000 IU per day must be taken under medical supervision. Toxicity can appear in some individuals at relatively low dosages and the symptoms may include nausea, dizziness, menstrual problems, skin changes and dryness, itchiness, irritability, vomiting, headaches and long term use can cause hair loss, bone and muscle pain, headache, liver damage, and an increase in blood lipid concentrations. Pregnant women must be careful as a high intake of this vitamin can cause birth defects.

Pro-vitamin A - beta-carotene does not cause toxicity. Be careful if you in the unlikely event run across polar bear on a menu - 500 gram (about ½ a pound) of polar bear liver will deliver about 9,000,000 IU to your diet - a very lethal dose. Headaches, blurred vision, loss of hair, drowsiness and diarrhea, enlargement of the spleen and liver can all be indications when your intake is too high.

Best used with

Take vitamin A with B group vitamins, vitamins C, D and E, choline, essential fatty acids together with calcium, phosphorus and zinc for the best results.

When more may be required

More of this vitamin is required when you consume alcohol, on a low-fat diet, or a diet high in polyunsaturated fatty acids, if you smoke or live in a polluted area. It may also be indicated if you suffer from diabetes or have an under-active thyroid gland. Be careful of vitamin A in pregnancy.

Enemy of vitamin A

Retinol is destroyed by light, high temperatures as well as when using copper or iron cooking utensils. Beta-carotene rich vegetables and fruit must not be soaked in water for long periods, since the nutrients can be lost like that.

Other interesting points

There seems to be no toxicity when ingesting large amounts of beta-carotene - you might however have a slightly orange colored skin, as the carotene gets stored in your skin.

Food sources of vitamin A

Liver, milk, egg-yolk, carrots, dark green leafy vegetables and yellow fruits are high in vitamin A or beta-carotene.