Nutritional deficiency diseases result primarily from a diet that does not have enough of the nutrients that are essential to health or development. Another cause is that an individual may not be able to utilize properly the nutrients consumed in the diet. Deficiency diseases may result from a person's abnormally high metabolic needs for a nutrient or from some imbalance in the nutrients ingested. Certain drugs or medicines may also affect nutrient use.
Deficiency diseases often result from insufficient food intake, or a poorly balanced diet, but may also be caused by ill health (diarrhea, parasitic infections, cancer, AIDS) or, especially in children, by inadequate care.
The most severe deficiency disease is starvation, where there is marked weight reduction, loss of fat and other tissues, including from the liver and intestines. Most systems are affected, including the body's immune system. The skin and hair become dry. Endocrine disturbances may occur, and in women amenorrhea is common. Diarrhea often develops, and the sufferer may die of secondary infection.
Nutritional deficiency contributes to much of the ill health in developing countries. The most important forms of malnutrition there are protein-energy malnutrition; iodine deficiency disorders; vitamin A deficiency; and nutritional anemias.
Humans obtain energy (measured in calories or joules) from carbohydrates, fat, and protein and also from alcohol. In the majority of societies the most available source of calories is carbohydrates, whereas fat and protein are less available. In general, as families or communities become more affluent, the proportion of fat and animal protein in the diet increases.
A failure to consume adequate quantities of food energy may lead to loss of weight or growth failure in children, wasting of tissues, and eventually starvation. The production of enzymes and hormones is impaired in severe protein deficiency. Young children living in poorer communities throughout the world commonly have protein-energy malnutrition (PEM). This condition is aggravated by common infections, such as diarrhea, and sometimes by the irregular intervals at which a child may have food to eat.
The two clinical forms of PEM are nutritional marasmus and kwashiorkor. Marasmus is due primarily to an energy (calorie) deficiency; in kwashiorkor, protein deficiency predominates. Mild or moderate PEM is much more common than these two severe forms and leads to a slow rate of growth, to poor development, to increased susceptibility to infections, and eventually to permanent physical stunting.
The most prevalent and important mineral deficiencies are iron deficiency, the most common cause of anemia; iodine deficiency, a cause of endemic goiter and mental retardation; low fluoride intake, which contributes to tooth decay; and zinc deficiency.
Among the major vitamin-deficiency diseases is xerophthalmia, which is due to vitamin A deficiency.
It can result in ulceration of the cornea of the eye, sometimes blindness, as well as increased mortality rates. Beriberi, a thiamine, or vitamin BN, deficiency, is commonly found among rice-eating peoples and occurs in alcoholics. Pellagra results from a deficiency in niacin and is associated with persons whose staple diet is corn or maize. A riboflavin, or vitamin BM, deficiency causes ariboflavinosis, in which there may be cracks of the lips and lesions in the genital areas. The macrocytic anemias (involving abnormally large red blood cells) result particularly from folic-acid deficiency during pregnancy and sometimes from BNM deficiency. Rickets and osteomalacia (softening of the bones) are due to vitamin D deficiency, and scurvy is due to vitamin C deficiency. Other vitamin deficiencies, such as vitamin K deficiency in the newborn and vitamin BR deficiency in those taking certain medications, areuch less important and less prevalent.
The specific treatment for each of these deficiency states is usually the medical provision of appropriate doses of the nutrient in question and also an assurance that foods rich in these nutrients are consumed in the diet. This latter approach is also the basis for prevention of these diseases. Some diseases may also be prevented by fortification of commonly eaten foods with nutrients, by various food supplement programs, by increasing local production of nutritious foods, and, in the long run, by better nutrition education.
PROBLEMS OF WORLD HEALTH
In recent years world concern has increased about hunger and malnutrition. In most parts of the world major famines have led to international action to reduce the extent of starvation. The World Health Organization (WHO), the Food and Agriculture Organization (FAO), and United Nations Children's Fund (UNICEF), all agencies of the UN, play important and different roles in trying to reduce the extent and seriousness of malnutrition, particularly in developing countries. They coordinate activities and attempt to establish international standards of classification and reporting; they also make recommendations about nutrient requirements for different population groups.
In the United States the Food and Nutrition Board of the National Academy of Sciences/National Research Council publishes Recommended Dietary Allowances (RDA) of all the important nutrients.