Iron in Nutrition

Abstract

These special articles on foods and nutrition have been prepared under the auspices of the Council on Foods and Nutrition. The opinions expressed are those of the authors and do not necessarily reflect the opinion of the Council. These articles will be published later as a Handbook of Nutrition.-Ed. In spite of evidence to the contrary, the idea is still current that when the diet is deficient in iron the red cells soon become deficient in hemoglobin (hypochromic) and smaller (microcytic) than normal. This idea is certainly not true for the healthy adult male or for healthy women after the menopause. It may sometimes be true for growing children and for women during their menstrual life or during pregnancy, or for any person who has lost or is losing considerable amounts of blood from some lesion of the body. Much remains to be learned about the metabolism and functions of iron, but of this we can be quite sure: a diet deficient in iron has not been known to produce iron deficiency except in the presence of increased needs for iron such as growth, pregnancy or blood loss.One basic fact is essential in any adequate consideration of iron deficiency: iron is an element and, unlike certain organic substances of the food which are necessary to the bod}-, such as the vitamins, it is not destroyed or used up in the body but is conserved and, if not excreted, can be utilized again and again. Another important fact concerning iron is that it is not excreted by either kidney or intestinal tract in appreciable quantities. It has been called a "one way substance;'' that is. it may be absorbed, or if not absorbed it will be eliminated in the stools, but, in any ordinary sense it is not excreted. The iron content of the normal human urine is very small. Lintzell regarded it as negligible, less than 0.02 mg. per liter. Marlow and Taylor found values for urinary iron ranging from 0.03 to 0.8 mg. in twenty-four hours. Lanyar, Lieb and Verdino 3 found less than 0.01 mg. of iron per liter of urine. The iron of the urine is not increased significantly even after destruction of the red blood cells by phenylhydrazine.4 It may be increased immediately after the administration of inorganic compounds parenterally.3 Hahn and his associates,5 in a study of dogs which were given radioactive iron as ferrous gluconate by vein, found an extra output of iron in the urine and feces for a few days after its injection (2 to 8 per cent of the total amount injected). Following this the urinary iron dropped to traces, but the stools contained from 0.05 to 0.4 mg. of radioactive iron daily. The bile contained insignificant amounts of iron, which confirms the findings of others. The authors considered the evidence conclusive that the dog excretes iron only with difficulty and in small amounts. Maddock and Heath6 decided from microscopic study of the gastrointestinal tract and of colonie explants on the abdominal walls of dogs before and after the administration of iron that iron cannot be observed to be excreted by these organs.Studies of the balanc...

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