Can vitamin A prevent blindness?

​What is VITAMIN A? It is a fat-soluble vitamin, which means it dissolves in fats. Vitamin A has different forms called retinoids: -preformed vitamin A retinol and retinyl esters (storage form of retinols) are found in liver, red meat, eggs, fish, milk, butter, cream. -provitamin A carotenoids (dietary precursors to retinol) are found in deep yellow, green and red plants. Cooking can destroy up to 40% of the vitamin A content of food. Once in the body, carotenoids are hydrolyzed in the small intestine and absorbed as retinol into the mucosal cells. Then, retinols are transported within chylomicrons to the blood to end up in the liver. The liver is major storage of vitamin A. Vitamin A is excreted through the faeces and urine. The body has limited capacity to dispose of vitamin A excess, so if we take too much of it, we can reach toxic levels. Vitamin A activity is expressed as microgram RE or international unit IU. The recommended daily intake of vitamin A from all sources is: -700 microgram RE or 2330 IU for women, -900 microgram RE or 3000 IU for men. Symptoms of vitamin A deficiency include night blindness, dry and thick skin, dental health problems, infertility. Prolonged dietary deprivation of vitamin A leads to blindness and mortality. If you are pregnant, or planning to become pregnant, talk to your doctor or pharmacist before taking vitamin A supplements. If taken in doses above 3000 microgram RE daily, vitamin A may cause birth defects. Early signs of toxicity include dry rough skin, cracked lips, coarse hair, sparse hair, alopecia of eyebrows, bone and joint pain, fatigue and malaise, nausea and vomiting, depression and schizophrenia. Later signs include irritability, increased intracranial pressure and headache, dizziness, liver cirrhosis, fibrosis, vomiting, hemorrhage and coma. People with chronic renal disease usually have high retinol levels in their blood and thus may be at greater risk of toxicity if they take vitamin A supplements. Betacarotene is not associated with vitamin A teratogenic effects or toxicity and is considered a safer option. Studies conducted in Africa recommended to use orange sweet potato, which is rich in betacarotene, to treat vitamin A deficiencies.

​In North Africa, children's blindness caused by fly-carried chlamydial eye infections was treated by giving yellow vegetables or vitamin A supplements to the children. In South Africa, children's death due to measles pneumonia was reduced by more than 50% with vitamin A supplementation.

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