Interactions of nutrition and infection.

Interactions between malnutrition and infection contribute directly to the health of individuals and communities. The relevance of this concept to the practice of clinical medicine, dentistry, and public health is supported by an imposing collection of evidence from the clinic, laboratory, and field. Malnutrition can interfere with any body mechanism that acts as a barrier to the multiplication or progress of infectious agents. This includes formation of specific antibodies, number and activity of phagocytes, integrity of skin, mucous membranes, and other tissues. Some of the less definite, nonspecific protective substances in body fluids are also affected by malnutrition. Infectious disease adversely influences the nutritional state in several indirect ways. Loss of appetite and intolerance for food result in metabolic changes. Cultural factors lead to substitution of less nutritious diets as a presumed therapeutic measure and to administration of purgatives, antibiotics, and other medicines that reduce digestion or absorption of specific nutrients. All of these may help to precipitate kwashiorkor in children subsisting on protein-deficient diets. Classical nutritional deficiencies precipitated by infection in individuals with borderline nutrient depletion include: keratomalacia due t avitaminosis-A; scurvey from lack of ascorbic acid; beriberi as a consequence of inadequate thiamin; pellagra resulting from insufficient niacin; macrocytic anemia due to folic acid or vitamin B12 deficiency; and microcytic anemia resulting from a shortage of iron. In well nourished individuals, body reserves and normal dietary intake assure that malnutrition will not result unless infection is prolonged.