Taken from the office of dietary supplements website. The office of dietary supplements is a part of the American national institute of health. In the website you can find various health information, including data sheets for most dietary supplements. This part is taken from the vitamin a dietary fact sheet-
Vitamin A deficiency is common in developing countries but rarely seen in the United States. Approximately 250,000 to 500,000 malnourished children in the developing world become blind each year from a deficiency of vitamin A . In the United States, vitamin A deficiency is most often associated with strict dietary restrictions and excess alcohol intake . Severe zinc deficiency, which is also associated with strict dietary limitations, often accompanies vitamin A deficiency. Zinc is required to make retinol binding protein (RBP) which transports vitamin A. Therefore, a deficiency in zinc limits the body’s ability to move vitamin A stores from the liver to body tissues.
Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt, it was known that night blindness could be cured by eating liver, which was later found to be a rich source of the vitamin . Vitamin A deficiency contributes to blindness by making the cornea very dry and damaging the retina and cornea .
Vitamin A deficiency diminishes the ability to fight infections. In countries where such deficiency is common and immunization programs are limited, millions of children die each year from complications of infectious diseases such as measles . In vitamin A-deficient individuals, cells lining the lungs lose their ability to remove disease-causing microorganisms. This may contribute to the pneumonia associated with vitamin A deficiency .
There is increased interest in early forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause obvious deficiency symptoms. This mild degree of vitamin A deficiency may increase children’s risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness. Children in the United States who are considered to be at increased risk for subclinical vitamin A deficiency include:
- toddlers and preschool age children;
- children living at or below the poverty level;
- children with inadequate health care or immunizations;
- children living in areas with known nutritional deficiencies;
- recent immigrants or refugees from developing countries with high incidence of vitamin A deficiency or measles; and
children with diseases of the pancreas, liver, or intestines, or with inadequate fat digestion or absorption.
A deficiency can occur when vitamin A is lost through chronic diarrhea and through an overall inadequate intake, as is often seen with protein-energy malnutrition. Low blood retinol concentrations indicate depleted levels of vitamin A. This occurs with vitamin A deficiency but also can result from an inadequate intake of protein, calories, and zinc, since these nutrients are needed to make RBP . Iron deficiency can also affect vitamin A metabolism, and iron supplements provided to iron-deficient individuals may improve body stores of vitamin A and iron .
Excess alcohol intake depletes vitamin A stores. Also, diets high in alcohol often do not provide recommended amounts of vitamin A . It is very important for people who consume excessive amounts of alcohol to include good sources of vitamin A in their diets. Vitamin A supplements may not be recommended for individuals who abuse alcohol, however, because their livers may be more susceptible to potential toxicity from high doses of vitamin A . A medical doctor will need to evaluate this situation and determine the need for vitamin A supplements.