The Iron Metabolism of Normal Young Women during Consecutive Menstrual Cycles

Abstract

The total iron exchanges of four normal young women on an adequate diet during consecutive menstrual cycles were determined over a period of 3 to 5 months by means of a continuous balance experiment. The total time of the experiment was divided arbitrarily into consecutive 5-day periods and a single foundation dietary was used for every subject during every period. Certain low-mineral foods were permitted ad libitum to meet the differing energy requirements of the subjects. Food composites which represented one-tenth the amount of all food eaten by each subject were made and analyzed for each period. Feces and urine collections were combined for each 5-day period and analyzed for iron. The menstrual flow was collected on cellulose pads for analysis. Records were kept of any additional blood losses and the results considered in the actual iron balance of the subjects. The average daily intakes of iron for the entire time for the four subjects were 13.61, 11.87, 10.03 and 11.71 mg. with corresponding balances between food and excreta of +0.72, +1.48, +0.71 and -0.20 mg. The average coefficient of variation was 11.9 for the iron in the food and 25.8 for that in the excreta. Although there were periods of negative and of positive balance for the subjects during the study, a negative balance never occurred when the intake of iron from food was 0.225 mg. or more per kilogram per day. No relation between time of iron storage and its loss during the menstrual period could be demonstrated. A supplement of 5 mg. of iron in the form of ferric ammonium citrate was given to one subject during her fourth and fifth menstrual cycles. This resulted in an increased excretion and a decreased retention of iron as compared with the cycles when she was not receiving the supplement. The average menstrual losses for the four subjects were 14.26, 22.84, 11.13 and 13.80 mg. of iron, respectively. The losses were relatively constant from period to period for the same subject. In nine of the sixteen menstrual cycles the subjects were in iron equilibrium or slight positive balance after the menstrual loss had been subtracted from the balance between the iron intake and iron excretion for each cycle. Only two subjects were able to compensate also for the iron loss in the venous blood samples which were taken in connection with another study. The other two subjects were in negative iron balance when this additional loss was included in calculating their actual iron balance for the entire study. All the subjects increased the hemoglobin content of their blood at least 1 gm. per 100 cc. during the experimental regime; the red cell content remained remarkably constant. The findings are discussed in relation to the iron requirement of these subjects and of other normal women. These subjects on a diet which contained 10 to 14 mg. of iron daily and fortified in other dietary essentials were receiving only their minimal requirement of this element. Calculations for the optimal daily allowance of iron for a 56 kilo. woman give results of 16 to 17 mg. which is somewhat higher than the 15 mg. recommended by Sherman. The results of this study together with the fact that the average dietary seldom contains even 15 mg. of iron indicate that the low hemoglobin values which are accepted as normal for women because of the drain due to menstruation may be a direct reflection of the use of diets habitually low in iron rather than due to the small periodic loss in the menses.