单项选择题

TEXT E
WHO, working closely with its Member States, other United Nations agencies and non-governmental organizations, is focusing on major crippling forms of malnutrition: protein-energy malnutrition, iodine deficiency disorders, vitamin A deficiency, and iron deficiency anaemia.
In some regions, such as sub-Saharan Africa and south Asia, stagnation of nutritional improvement combined with a rapid rise in population has resulted in an actual increase in the total number of malnourished children. Currently, over two-thirds of the world’s malnourished children live in Asia, followed by Africa and Latin America.
Various types of micronutrient malnutrition are important causes of disability in themselves and often underlie other types of morbidity. Their prevalence is even more widespread than that of protein-energy malnutrition.
In sheer numbers, iron is the most prevalent micronutrient deficiency, with nearly 1,990 million people being anemic and 3,600 million iron-deficient. Iron deficiency is present when body iron stores are depleted.
Mainly women of reproductive age and children under five are affected by iron deficiency, with prevalences hovering around 50% in developing countries. Among various regions of the world, it is south Asia which is hit hardest with prevalences reaching 80% in some countries. In infants and young children even mild anaemia is associated with impaired intellectual as well as physical development. In older children and adults iron deficiency reduces work capacity and output. It also leads to increased absenteeism and accidents at work. During pregnancy, maternal anaemia aggravates the effects of hemorrhage at childbirth and is a major contributing factor to maternal mortality.
While there is no single remedy, a combination of several preventive approaches is believed to work best. Dietary improvement includes consumption of iron and vitamin C-rich foods and foods of animal origin, and avoiding drinking tea or coffee with or soon after meals. Iron fortification of foods, particularly of staple cereals, is practiced in a growing number of countries. Iron supplementation is the most common approach, particularly for pregnant women.
Another major problem is iodine deficiency disorders (IDD). Iodine deficiency remains the single greatest cause of preventable brain damage and mental retardation worldwide. WHO estimated in 1990 that 1,570 million people, or about 30% of the world’s population, were at risk of IDD.
Insufficient intakes of iodine in pregnancy and early childhood result in impaired mental development of young children. Even marginal deficiency may reduce a child’s mental development by as much as 10 IQ points.
The third major micronutrient deficiency is vitamin A deficiency which is officially recognized in 76 countries as a major public health problem. The number of children under five affected clinically is estimated at 2.8 million, with 258 million being diagnosed as having a biochemical deficiency. The highest prevalence and numbers are in Southeast Asia.
Depletion occurs when the diet contains too little vitamin A to replace the amount used by tissues. The consequences include night blindness and the destruction of the cornea, Vitamin A deficiency is the most common cause of blindness in young children. Where clinical vitamin A deficiency is a public health problem, young child mortality rates are raised by 20% to 30%.
There are several tried and tested ways of preventing and treating vitamin A deficiency, including improved production and consumption of foods rich in vitamin A or carotene, especially dark-green leafy vegetables and fruits, and liver, eggs and milk products if available. Fortification of fats has been successfully introduced in industrialized countries while the same technique using sugar proved to be equally successful in Central America. Another useful strategy is supplementation with large doses of vitamin A every 4 to 6 months for children of pre-school age and lactating women.
Mental development of young children is impaired mainly by ______.