Specific deficiencies versus growth failure: type I and type II nutrients.

Abstract

A child responds to a deficiency of an essential nutrient either by continuing to grow and consuming body stores with eventual reduction in the bodily functions (Type I) or by reducing growth and avidly conserving the nutrient to maintain the concentration of the nutrient in the tissues (Type II). Examples of Type I nutrient deficiency are anemia (iron deficiency), beri-beri (thiamin deficiency), pellagra (niacin or nicotinic acid deficiency), scurvy (vitamin C or ascorbic acid deficiency), xerophthalmia (vitamin A or retinol deficiency) and iodine deficiency disorders. Diagnosis is relatively simple via clinical symptoms and measurement of the concentration of the nutrient itself. There are no characteristic symptoms to distinguish which Type II nutrient deficiency an individual has; all deficiencies result in the poor growth, stunting, and wasting generally ascribed to protein-energy malnutrition. In Type II, growth stops, the body starts to conserve the nutrient, and its excretion falls to very low levels. In severe deficiency the body may start to break down its own tissues and the reduction of appetite accompanies this condition. An animal can die from zinc deficiency even though it is has a normal concentration of zinc in its tissues, but it can respond rapidly to small amount of dietary zinc. The mechanisms by which the body stops growing in response to nutritional lack are similar to the hormonal picture seen in endocrine disease (reduction of the production of the hormonal mediators of growth, down-regulation of receptors, and reduction of protein synthesis). Growth failure is the clinical sign characteristic of a diet deficient in protein, zinc, magnesium, phosphorus, and potassium. Wasting may be also ascribed to toxins, infection, worms, or persistent diarrhea. Anorexia is another common response in nutrient deficiency. Only a supplementation diet with a balance of nutrients will promote rapid recovery.