<P> The richest animal sources of Vitamin A (retinol) are livers like beef liver (one ounce provides around 8,000 IUs) and cod liver oil (one teaspoon provides around 4,500 IUs). </P> <P> Vitamin A deficiency is one of several hypovitaminoses implicated in follicular hyperkeratosis . </P> <P> The major cause is roughage which include few animal sources of pre-formed vitamin A . In addition to dietary problems, there are other causes of VAD . Iron deficiency can affect vitamin A uptake . Excess alcohol consumption can deplete vitamin A, and a stressed liver may be more susceptible to vitamin A toxicity . People who consume large amounts of alcohol should seek medical advice before taking vitamin A supplements . In general, people should also seek medical advice before taking vitamin A supplements if they have any condition associated with fat malabsorption such as pancreatitis, cystic fibrosis, tropical sprue and biliary obstruction . Other causes of Vitamin A deficiency are inadequate intake, fat malabsorption, or liver disorders . Deficiency impairs immunity and hematopoiesis and causes rashes and typical ocular effects (e.g., xerophthalmia, night blindness). </P> <P> Along with poor diet there is a large amount of infection and disease present in many developing communities . Infection is very draining on vitamin A reserves and this vitamin A deficit leaves the individual more susceptible to infection (Combs, 1991); increased documentation of xerophthalmia has been seen after an outbreak of measles and the varying stages of xerophthalmia become a good reference point for the extent of deficiency (with mortality increasing with severity of the eye disease). In a longitudinal study of preschool Indonesian children it was found that susceptibility to disease increased nine times when severe VAD was present (Dole 2009). </P>

Why is vitamin a deficiency common in developing countries
find me the text answering this question