Iron absorption and iron status related to diet : an experimental and epidemiological study

Sammanfattning: The absorption of iron from the diet is a major determinant of the iron status of an individual. Accurate measures of iron absorption are thus essential in the determination of the effects of diet composition on iron absorption and status.The aim of these studies have firstly been to investigate different methods to measure iron absorption and effects of diet in both rats and humans. Secondly to describe variations in iron status in a general population and to relate the variations to diet.Experimental studies in rats: The most important factors determining the availability of iron from the diet to growing rats appears to be the concentration of iron in the diet and the iron status of the rats. The type of cereal |rain in the diet and the diet phytate and fiber concentrations were of far less importance. The absorption of Fe from test meals, the iron balance over a period of a few days and the blood hemoglobin and serum and liver iron concentrations were in good general agreement on the effects of diet and iron status on the bioavailability of iron from grain diets. The extent of coprophagy in rats is not affected by diet or iron status and did not affect iron absorption appreciably.Effect of dairy products on iron absorption in man: The effect of milk and fermented milk on iron absorption was studied in nine ileostomy subjects. We found no decrease in iron absorption during two three-week periods on a high calcium (milk) diet. The results of the present study differ from those studies in which the absorption of radioiron from test meals was measured, which have shown a pronounced effect of high calcium levels. We believe that these differences in results were caused by differences in experimental design and choice of measurement method. Our results support earlier findings that the iron status of the subject rather than the bioavailability of dietary iron is the major factor determining absorption of dietary non-heme iron.Measurement of iron absorption from single meals and daily diets in humans using radioiron: Ten ileostomy subjects were given the same composite diet for all three meals each day for five consecutive days (meal proportion ratio 1:2:4 for breakfast, lunch and dinner respectively). The iron absorption from a low-fiber diet measured from the morning meals (55Fe) was almost 80% higher than the average iron absorption measured from all meals (59Fe) during the last two days on this diet. The iron absorption from a high fiber diet eaten at breakfast was almost 50% higher than the daily average absorption. This suggests that all meals of the day should be labeled with radioiron and not just the morning meal.Population studies of diet and iron status: In a randomly selected population in Northern Sweden lower iron status was associated with a high intake of dairy products in women (25-44 yr.). The striking result was however that iron status was not related to other major variations in dietary intake, particularly intake of energy and iron. No correlation could be demonstrated between iron status measured as ferritin, serum iron or TIBC and the estimated intakes of calcium, fiber, ascorbic acid, meat, tea or coffee, all of which are known to be factors which influence the bioavailability of iron. On the population level, factors other than diet, e.g. menstruation and metabolic factors, were more important than diet as determinants of iron status.