vitamin A deficiency


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Vitamin A Deficiency

 

Definition

Vitamin A deficiency exists when the chronic failure to eat sufficient amounts of vitamin A or beta-carotene results in levels of blood-serum vitamin A that are below a defined range. Beta-carotene is a form of pre-vitamin A, which is readily converted to vitamin A in the body. Night blindness is the first symptom of vitamin A deficiency. Prolonged and severe vitamin A deficiency can produce total and irreversible blindness.

Description

Vitamin A (called retinol in mammals) is a fat-soluble vitamin. The recommended dietary allowance (RDA) for vitamin A is 1.0 mg/day for the adult man and 0.8 mg/day for the adult woman. Since beta-carotene is converted to vitamin A in the body, the body's requirement for vitamin A can be supplied entirely by beta-carotene. Six mg of beta-carotene are considered to be the equivalent of 1 mg of vitamin A. The best sources of vitamin A are eggs, milk, butter, liver, and fish, such as herring, sardines, and tuna. Beef is a poor source of vitamin A. Plants do not contain vitamin A, but they do contain beta-carotene and other carotenoids. The best sources of beta-carotene are dark-green, orange, and yellow vegetables; spinach, carrots, oranges, and sweet potatoes are excellent examples. Cereals are poor sources of beta-carotene.
Vitamin A is used for two functions in the body. Used in the eye, it is a component of the eye's light-sensitive parts, containing rods and cones, that allow for night-vision or for seeing in dim-light circumstances. Vitamin A (retinol) occurs in the rods. Another form of Vitamin A, retinoic acid, is used in the body for regulating the development of various tissues, such as the cells of the skin, and the lining of the lungs and intestines. Vitamin A is important during embryological development, since, without vitamin A, the fertilized egg cannot develop into a fetus.

Causes and symptoms

Vitamin A deficiency occurs with the chronic consumption of diets that are deficient in both vitamin A and beta-carotene. When vitamin A deficiency exists in the developed world, it tends to happen in alcoholics or in people with diseases that affect the intestine's ability to absorb fat. Examples of such diseases are celiac disease (chronic nutritional disorder), cystic fibrosis, and cholestasis (bile-flow failure or interference). Vitamin A deficiency occurred in infants during the early 1900s in Denmark. The deficiency resulted when milk fat was made into butter for export, leaving the by-product (skimmed milk) for infant feeding. Vitamin A deficiency has taken place in infants in impoverished populations in India, where the only foods fed to the infants were low in beta-carotene. Vitamin A deficiency is also common in areas like Southeast Asia, where polished rice, which lacks the vitamin, is a major part of the diet.

Key terms

Bitot's spots — Bitot's spots are superficial, foamy gray, triangular spots on the white of the eyeball.
Carotenoids — Carotenoids are yellow to deep-red pigments.
Conjunctiva — The conjunctiva is a clear layer of cells that covers the eye and directly contacts the atmosphere. The conjunctiva is about five-cells thick.
Cornea — The cornea is a clear layer of cells that covers the eye, just under the conjunctiva. The cornea is about 50-cells thick.
Fat-soluble vitamin — Fat-soluble vitamins can be dissolved in oil or in melted fat. Water-soluble vitamins can be dissolved in water or juice.
Keratomalacia — Keratomalacia is ulceration of the cornea.
Recommended Dietary Allowance (RDA) — The Recommended Dietary Allowances are quantities of nutrients in the diet that are required to maintain good health in people. RDAs are established by the Food and Nutrition Board of the National Academy of Sciences, and may be revised every few years. A separate RDA value exists for each nutrient. The RDA values refer to the amount of nutrient expected to maintain good health in people. The actual amounts of each nutrient required to maintain good health in specific individuals differ from person to person.
Xerophthalmia — Xerophthalmia is a dry, thickened, lusterless condition of the eyeball resulting from vitamin A deficiency.
The earliest symptom of vitamin A deficiency is night blindness. Prolonged deficiency results in drying of the conjunctiva (the mucous membrane that lines the inner surface of the eyelids and extends over the forepart of the eyeball). With continued vitamin A deficiency, the drying extends to the cornea (xerophthalamia). The cornea eventually shrivels up and becomes ulcerated (keratinomalacia). Superficial, foamy gray triangular spots may appear in the white of the eye (Bitot's spots). Finally, inflammation and infection occur in the interior of the eye, resulting in total and irreversible blindness.

Diagnosis

Vitamin A status is measured by tests for retinol. Blood-serum retinol concentrations of 30-60 mg/dl are considered in the normal range. Levels that fall below this range indicate vitamin A deficiency. Night blindness is measured by a technique called electroretinography. Xerophthalamia, keratinomalacia, and Bitot's spots are diagnosed visually by trained medical personnel.

Treatment

Vitamin A deficiency can be prevented or treated by taking vitamin supplements or by getting injections of the vitamin. The specific doses given are oral retinyl palmitate (110 mg), retinyl acetate (66 mg), or injected retinyl palmitate (55 mg) administered on each of two successive days, and once a few weeks later if symptoms are not relieved.

Prognosis

The prognosis for correcting night blindness is excellent. Xerophthalamia can be corrected with vitamin A therapy. Ulcerations, tissue death, and total blindness, caused by severe vitamin A deficiency, cannot be treated with vitamin A.

Prevention

Vitamin A deficiency can be prevented by including foods rich in vitamin A or beta-carotene as a regular component of the diet; liver, meat, eggs, milk, and dairy products are examples. Foods rich in beta-carotene include red peppers, carrots, pumpkins, as well as those just mentioned. Margarine is rich in beta-carotene, because this chemical is used as a coloring agent in margarine production. In Africa, Indonesia, and the Philippines, vitamin A deficiency is prevented by public health programs that supply children with injections of the vitamin.

Resources

Books

Brody, T. Nutritional Biochemistry. San Diego: Academic Press, Inc., 1998.

vitamin A deficiency

A condition characterised by night blindness, keratomalacia, increased urogenital and nasopharyngeal infections, and dry eyes.

vitamin A deficiency

A condition characterized by night blindness, keratomalacia, ↑ urogenital and nasopharyngeal infections, dry eyes; VAD is rare, as many foods contain or are supplemented with vitamin A. toxicity

vitamin A deficiency 

A deficiency of vitamin A (also called retinol) leads to interference with growth, atrophy of epithelial tissues resulting in keratomalacia, corneal ulcerations, xerophthalmia with Bitot's spots, reduced resistance to infection of mucous membranes, and abnormal production and regeneration of rhodopsin resulting in night blindness. Management includes a balanced diet and may require large vitamin A supplement with a topical antibiotic to prevent secondary infections. See carotene; hemeralopia.

Patient discussion about vitamin A deficiency

Q. Recently I came to know after a test that I am vitamin D deficient so how much vitamin D should I take? I am 26 yrs old and I have fibromyalgia. Recently I came to know after a test that I am vitamin D deficient so how much vitamin D should I take?

A. what is a normal level of vitamin d for a 65 yr old woman?

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References in periodicals archive ?
8% of all healthy years of life lost (YLLs) in South Africa in 2000) were associated with vitamin A deficiency (Table III).
Vitamin A deficiency is a public health problem among preschool children in South Africa, with 33.
Vitamin A deficiency accounted for 3 069 deaths in children aged 0-4 years (3.
This is also lower than the estimated 20% of maternal deaths worldwide, and is a result of the relatively low prevalence of vitamin A deficiency among pregnant women in South Africa.
8% of all DALYs in South Africa in 2000, are attributable to vitamin A deficiency.
Given the high prevalence of HIV in South Africa, it is important to consider the possible role of vitamin A deficiency in HIV-related morbidity and mortality.
Our estimate is likely to be an underestimation of the attributable burden due to vitamin A deficiency, since we have not quantified this impact.
The burden of disease attributable to vitamin A deficiency estimated in the present study was based on data from the SAVACG study, which were collected in 1994.
A national survey on the micronutrient status of preschool children and women is currently underway, and when these data become available it is suggested that the risk attributed to vitamin A deficiency be recalculated and the situation reevaluated.
Dr Robert Black, a member of the Global and Regional Comparative Quantification of Health Risks Assessment Vitamin A Deficiency Team, was extremely helpful in providing advice and guidance and in obtaining relative risks and drafts of the global review chapters.
Extent of vitamin A deficiency among preschool children and women of reproductive age.