OBJECTIVES
To study factors determining iron balance in menstruating women by examining the relationships between total iron requirements, based on menstrual iron losses and basal iron losses, and serum ferritin concentration, transferrin saturation, blood haemoglobin concentration, bone marrow haemosiderin and absorption of iron from a test dose of ferrous sulphate (0.56 mg Fe).
SUBJECTS
The study was made in 203 women all aged 38 years, randomly selected from the census register of Göteborg. The study was originally made in 1968-69. Serum ferritin in frozen sera was first analysed in 1978. Reanalyses, calibrated to the International Standard 80/602, and studies on the effect of storage of sera, were made in 1992. This allowed a complete re-examination of the importance of different determinants of iron balance in women.
RESULTS
With increasing iron requirements there was an increase in iron absorption, and a decrease in serum ferritin concentration and transferrin saturation. Above a certain level of iron requirement there was a rather sudden decrease in haemoglobin concentration and in stainable iron in bone marrow smears, indicating the critical level of iron requirements in these women that could be balanced by an increased iron absorption from the present diet. This level represents the maximal adaptation to maintain iron balance in an iron-replete state that can be achieved with this diet and corresponds to a prevalence of iron deficiency of about 25%.
CONCLUSIONS
The continuous regulation of iron absorption from iron deficiency to iron repletion has a critical balance point determined by the properties of the diet.