Vitamin A (retinol) is necessary for the function of light-sensitive nerve cells (photoreceptors) in the eye’s retina and thus helps maintain night vision. It also helps keep the skin and the lining of the lungs, intestine, and urinary tract healthy and protects against infections. Good sources of vitamin A include fish liver oils, liver, egg yolks, butter, cream, and fortified milk. (See also Overview of Vitamins.)
Carotenoids, such as beta-carotene, are pigments in fruits and vegetables that give them their yellow, orange, or red color. Once consumed, carotenoids are slowly converted to vitamin A in the body. Carotenoids are best absorbed from cooked or homogenized vegetables served with some fat or oil. Good sources of carotenoids are dark green, yellow, and orange vegetables and yellow and orange fruits.
Vitamin A deficiency is usually caused by
This deficiency is common in areas of the world where people do not eat enough of foods that are good sources of vitamin A, such as
For example, vitamin A deficiency occurs in southern and eastern Asia, where regular rice, which contains no vitamin A, is the main food. Golden rice has higher amounts of beta carotene, and may decrease vitamin A deficiency.
Disorders that impair the intestine’s absorption of fats can reduce the absorption of the fat-soluble vitamin A and increase the risk of vitamin A deficiency. These disorders include chronic diarrhea, celiac disease, cystic fibrosis, certain pancreatic disorders, and blockage of the bile ducts. Surgery on the intestine or pancreas can have the same effect.
Liver disorders can interfere with the storage of vitamin A. (Most of the body's vitamin A is stored in the liver.)
Vitamin A deficiency is common among people who have had a severe deficiency of protein and calories (protein-energy undernutrition) for a long time. People with this disorder do not consume enough vitamin A, and storage and use of vitamin A is impaired.
An early symptom of vitamin A deficiency is night blindness, which is caused by a disorder of the retina. Soon thereafter, the whites (conjunctiva) and corneas of the eyes may become dry and thick—a condition called xerophthalmia. Xerophthalmia is particularly common among children who have a severe deficiency of calories and protein, which includes inadequate intake of vitamin A. Foamy deposits (Bitot spots) may appear in the whites of the eyes. The dry cornea may soften and deteriorate, and blindness may result. Vitamin A deficiency is a common cause of blindness in developing countries.
The skin becomes dry and scaly, and the lining of the lungs, intestine, and urinary tract thicken and stiffen.
The immune system does not function normally, making infections more likely, particularly in infants and children.
Children’s growth and development may be slowed. More than half of children with severe vitamin A deficiency may die.
Doctors suspect vitamin A deficiency based on symptoms, such as night blindness.
Doctors measure the level of vitamin A in the blood. However, levels do not decrease until the deficiency is severe because the body stores large amounts of vitamin A.
If people have problems seeing in the dark, eye tests, such as electroretinography, may be done to determine whether vitamin A deficiency is the cause.
To help confirm vitamin A deficiency, doctors may give people vitamin A supplements to see whether they relieve symptoms.
To help prevent vitamin A deficiency, people should eat dark green leafy vegetables, yellow and orange fruits (such as papayas and oranges), carrots, and yellow vegetables (such as squash and pumpkin). Other food sources include milk and cereals that are fortified with vitamin A, liver, egg yolks, and fish liver oils. The carotenoids that give fruits and vegetables their yellow, orange, or red color and that are converted to vitamin A in the body, are best absorbed from cooked or homogenized vegetables served with some fat or oil.
Children who live in developing countries and are at risk of vitamin A deficiency should take vitamin A supplements.