Geographical distribution and recent changes in world supply of vitamin A.

Deficiency of vitamin A mainly affects infants and children up to the age of five years, and is often associated with protein-energy deficiency. The earliest symptom is night blindness. The most serious clinical manifestation is xerophthalmia which, depending upon the severity of the deficiency, may lead to partial or total blindness. Hypovitaminosis A is in fact a major cause of preventable blindness and must therefore be considered a serious public health problem. Hypovitaminosis A occurs in many developing countries and is particularly prevalent in South and East Asia. While the incidence and degree of severity varies from country to country, the population groups most affected are those of low socioeconomic status, usually with defective diets and living in poor sanitary environments. Poor dietary intake, however, appears to be the principal factor. The analysis that follows assesses the dynamics of the potential per caput supply situation as revealed by aggregate data at national level.