A very brief summary of the leading facts regarding the normal nutritive relations of iron may well precede the discussion of the amount required.

Iron is an essential element of hemoglobin and of the chromatin substances, i.e. of the body constituents most directly concerned with the processes of oxidation, secretion, reproduction, and development. The substances thus fundamentally connected with metabolism processes contain their iron in firm organic combination, as a constituent of their characteristic proteins; and the normal materials for the production of these body constituents are the similar iron-protein compounds of the food.

The iron of the food is absorbed from the small intestine, enters the circulation by way of the lymph, and is deposited mainly in the liver, spleen, and bone marrow. Its final elimination takes place mainly through the walls of the intestines.

Both inorganic and synthetically prepared organic forms of iron are absorbed from the same part of the digestive tract, stored in the same organs, and eliminated by the same paths as the iron of the food. These medicinal forms of iron often stimulate the production of hemoglobin and red blood corpuscles.

Whether medicinal iron actually serves as material for the construction of hemoglobin is not positively known, but we have what appears to be good evidence that food iron is assimilated and used for growth and for the regeneration of hemoglobin to much better advantage than are inorganic or synthetic forms, and that when medicinal iron increases the production of hemoglobin, its effect is more beneficial in proportion as the food iron is more abundant - a strong indication that the medicinal iron acts by stimulation rather than as material for the construction of hemoglobin.

Evidently, then, we should look to the food rather than to medicines or mineral waters for the supply of iron needed in normal nutrition.

Comparatively few experiments upon the amount of food iron required for the maintenance of equilibrium in man have been made. Cetti and Breithaupt eliminated 0.0073 and 0.0077 gram per day, respectively, when fasting. Three men observed by Stockman while receiving in the food about 0.006 gram each per day eliminated 0.0063, 0.0093, and 0.0115 gram, respectively. Von Wendt found his requirements to range in a number of experiments on different diets from 0.008 to 0.016 gram per day, the largest amount being required in a case where the diet was deficient in calcium. In three experiments by Sherman in which the food contained 0.0057 to 0.0071 gram of iron there was metabolized 0.0055, 0.0087, and 0.0126 gram per day, respectively, and here also the amount of iron which sufficed for equilibrium when taken in the form of bread and milk (a diet rich in calcium) was insufficient when taken in the form of a diet (poor in calcium) consisting of bread and egg white, or bread alone. In this case, however, the difference in the economy of the metabolism of the iron may have been due not simply to the change in the calcium content of the food, but also to a superior nutritive value of the iron compounds of milk over those of bread and to the fact that the general conditions of digestion and nutrition were better when milk was included in the diet than when it was excluded. The nitrogen, phosphorus, calcium, and iron balances for two of these experiments performed upon the same man and with diets practically alike in energy value and protein content, are shown in the following table:

Comparison Of Balances Of Different Elements

Here, although the nitrogen balance was practically alike on the two diets, there was on the bread and milk diet practical equilibrium of phosphorus and iron and a storage of calcium, while on the diet of bread and egg white there were noteworthy losses of all three of these elements.

Returning to the problem of the quantitative determination of the iron requirement it will be seen that in the cases in which the intake and output of iron have been determined, the requirement appears to have varied with individuals and with the nature of the diet from 0.006 to 0.016 gram (6 to 16 milligrams) of iron per man per day.

We might conclude from these results that a daily allowance of 10 to 12 milligrams of food iron should suffice for the maintenance of iron equilibrium in an average man under favorable conditions, but until the conditions which determine a larger metabolism of iron are more clearly defined, it would seem desirable to set a higher standard, perhaps 15 milligrams of food iron per man per day.

In calculating the iron requirement for a family dietary, it is well to make the allowance for women and children more liberal than would be indicated by their total food requirement. A woman requiring eight tenths as much food as a man will probably require more than eight tenths as much iron, and a child requiring half as much food may easily require more than half as much iron; for the influence of menstruation, pregnancy, and lactation in women and of growth and development in children may reasonably be expected to affect the demand for iron to an even greater extent than they affect the requirement for total food. It is probable that pregnancy and lactation increase the iron requirement of the mother by at least 3 milligrams per day, and at other times the losses of blood in menstruation must call for a greater intake of iron than would be needed by a healthy man of equal energy and protein requirement.

Since milk is the sole food of young mammals during a considerable period of rapid growth, Bunge was surprised to find only small amounts of iron in milk ash. Comparing the composition of the ash of milk with that of the newborn animals of the same species, it was found that, while other constituents occurred in nearly the same relative proportions, the iron was six times as abundant in the ash of the young animal as in that of the milk on which it was nourished. That the suckling animal grows rapidly and increases its blood supply in spite of this apparent deficiency of iron in its food is due to the fact that the body contains a reserve supply of iron at birth. In confirmation of this statement Bunge and his pupils have published many analyses showing that the percentage of iron in the entire organism is highest at birth, and that during the suckling period the amount of iron in the body remains about constant, notwithstanding the increase in body weight.

In all cases in which the young depend entirely upon the milk of the mother during the suckling period the body constituents of the young must evidently be derived entirely from the maternal organism either before birth through the placenta or after birth through the milk glands of the mother and the digestive tract of the young. Since disordered digestion may readily lead to defective absorption of the iron of the food, nature apparently takes the precaution of conveying the necessary iron from mother to offspring mainly by the safer method, i.e. through the placenta. Hence in the case of animals which feed solely upon milk for some time after birth, a relatively large amount of iron is stored before birth for use in the formation of hemoglobin during the suckling period. This has been shown by analysis to be true of children, puppies, kittens, and rabbits. On the other hand, guinea pigs, which feed on green leaves or other food rich in iron from the first day of life, are born without this reserve store of iron (Bunge). From recent analyses it appears that the percentage of iron in the human body is about three times as high at birth as at maturity. If it be assumed, as indicated by Bunge's work, that during the milk feeding of infancy the amount of iron in the body remains about constant, it would follow that the percentage of iron in the child's body would be reduced to that in the adult when the body weight becomes about three times what it was at birth - usually when a little over one year old, - and that from this time on throughout the period of growth, care should be taken that the food is sufficiently rich in iron to provide not only for equilibrium, but also for the constantly increasing blood supply.