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In iron-depleted women without anemia, oral iron supplements induce an increase in serum hepcidin (SHep) that persists for 24 hours, decreasing iron absorption from supplements given later on the same or next day. Consequently, iron absorption from supplements is highest if iron is given on alternate days. Whether this dosing schedule is also beneficial in women with iron-deficiency anemia (IDA) given high-dose iron supplements is uncertain. The primary objective of this study was to assess whether, in women with IDA, alternate-day administration of 100 and 200 mg iron increases iron absorption compared to consecutive-day iron administration. Secondary objectives were to correlate iron absorption with SHep and iron status parameters. We performed a cross-over iron absorption study in women with IDA (n=19; median hemoglobin 11.5 mg/dL; mean serum ferritin 10 mg/L) who received either 100 or 200 mg iron as ferrous sulfate given at 8 AM on days 2, 3 and 5 labeled with stable iron isotopes 57Fe, 58Fe and 54Fe; after a 16-day incorporation period, the other labeled dose was given at 8 AM on days 23, 24 and 26 (days 2, 3 and 5 of the second period). Iron absorption on days 2 and 3 (consecutive) and day 5 (alternate) was assessed by measuring erythrocyte isotope incorporation. For both doses, SHep was higher on day 3 than on day 2 (P<0.001) or day 5 (P<0.01) with no significant difference between days 2 and 5. Similarly, for both doses, fractional iron absorption (FIA) on days 2 and 5 was 40-50% higher than on day 3 (P<0.001), while absorption on day 2 did not differ significantly from day 5. There was no significant difference in the incidence of gastrointestinal side effects comparing the two iron doses (P=0.105). Alternate day dosing of oral iron supplements in anemic women may be preferable because it sharply increases FIA. If needed, to provide the same total amount of iron with alternate day dosing, twice the daily target dose should be given on alternate days, as total iron absorption from a single dose of 200 mg given on alternate days was approximately twice that from 100 mg given on consecutive days (P<0.001). In IDA, even if hepatic hepcidin expression is strongly suppressed by iron deficiency and erythropoietic drive, the intake of oral iron supplements leads to an acute hepcidin increase for 24 hours. The study was funded by ETH Zürich, Switzerland. This study has been registered at www.clinicaltrials.gov as #NCT03623997.
Anemia affects ~33% of the world population and accounts for 8.8% of global disability. 1 Iron deficiency (ID) is considered the most prevalent cause of anemia globally. 1 In the United States, nearly 10% of 12 to 49-year-old females have ID. 1 , 2 Oral iron supplementation with ferrous sulfate (FeSO4) is recommended to treat ID and iron deficiency anemia (IDA). 3 Because iron absorption from oral supplements tends to be low, current recommendations call for daily provision of high doses of FeSO4, in the range of 60-200 mg, preferably split into 2 or 3 daily doses. 4 – 7 With larger iron doses, 8 the proportion of the dose absorbed, termed the fractional iron absorption (FIA), decreases, and large amounts of unabsorbed iron can cause gut inflammation 9 , 10 and increase free radical production and peroxidation in the gut mucosa. 11 , 12 This may result in gastrointestinal side effects, which are common 9 and typically dose dependent. 13 Furthermore, an increase in colonic iron can reduce abundances of beneficial commensal gut bacteria and increase abundances of potential enteropathogens. 14 , 15
Hepcidin, the central systemic controller of iron homeostasis in mammals is a 25-amino acid peptide mainly produced by the liver, and is regulated by iron, hypoxia, inflammation and erythropoiesis. 16 Hepcidin binds to ferroportin, mainly expressed on enterocytes, hepatocytes and macrophages, leading to internalization and degradation of ferroportin. Thus, high serum hepcidin (SHep) reduces dietary iron absorption and recycling of iron from senescent erythrocytes. Large oral doses of iron acutely increase SHep in a dose-dependent fashion, with the increase in SHep persisting for ~24 hours (h). 8 , 17 The increase after iron administration is distinct 18 from the natural circadian increase in SHep over the day. 19 We previously showed that twice daily administration of 60 mg oral iron sharply augments the circadian SHep increase and results in higher SHep on the next day compared to once daily dosing with 120 mg iron. 17
In iron-depleted young women given doses ≥60 mg of oral iron in the morning, SHep increases and is followed by a decrease in iron absorption on the following day. 8 Consequently, alternate day dosing results in a higher FIA compared to daily dosing. 8 In a study comparing iron absorption from 60 mg doses during 28 days of alternate day versus 14 days of consecutive day supplementation, FIA was significantly higher (+33%) with alternate day dosing. 17 In addition, due to the acute SHep increase after an oral iron dose, splitting a dose into two daily divided doses did not increase iron absorption. 17 However, these studies were conducted in iron-depleted women without anemia. Whether oral iron supplements, given at higher doses in women with IDA also induce an acute SHep increase and inhibit absorption of daily doses of iron is uncertain. 20
Besides the iron-induced increase in SHep, a putative ‘mucosal block’ may decrease iron absorption from daily iron doses. According to the ‘mucosal block’ theory, enterocytes exposed to a large dose of iron will not absorb subsequent iron doses until they are replaced by new enterocytes after five to six days; therefore, provision of iron doses at weekly intervals might increase absorption. 21 If the increase in SHep subsides after 48 h, any residual inhibition on absorption would be consistent with this view of the ‘mucosal block’. The World Health Organisation recommends weekly intermittent iron doses in women who experience significant side effects taking oral iron doses. 22 Therefore, the aim of our study was to measure the magnitude and duration of the acute SHep increase after high-dose oral iron supplementation and the effect on iron absorption in women with IDA. Our hypotheses regarding women with IDA were: a) single oral iron doses of 100 and 200 mg acutely increase SHep and this increase persists for 24 h, but not 48 h; b) FIA from both doses would be lower on the following day, but not differ from baseline 48 h post administration (alternate day dosing), suggesting there is no ‘mucosal block’; and c) FIA would be lower from the 200 mg dose than the 100 mg dose.
We recruited healthy women participating in the blood donation drive at the University of Zürich, and we conducted this study at the Human Nutrition Laboratory of the ETH Zürich, Switzerland. Detailed inclusion criteria are described in the Online Supplementary Materials and Methods. In this cross-over study, we compared iron absorption from consecutive and alternate day dosing in women with IDA, using 100 and 200 mg doses of iron as ferrous sulfate (FeSO4). This study was approved by the Cantonal Ethics Committee in Zürich, Switzerland. All participants gave informed written consent.
Participants went through two study cycles of 6 days each, with 16 days in between ( Figure 1 ). To all subjects, we administered oral doses of FeSO4 in the morning on two consecutive days (days 2 and 3) and a third dose 48 h later (day 5), each dose was labeled with 57 Fe, 58Fe or 54 Fe. Subjects were randomly assigned to first receive either three doses of 100 mg or three doses of 200 mg. They were given the iron dose under standardized conditions. Detailed supplement administration is described in the Online Supplementary Material and Methods. On day 1, before iron supplementation, baseline venipuncture blood samples were taken at 8:00 AM and at 4:00 PM. Iron was administered at 8:00 AM on days 2, 3 and 5. Blood samples were taken at 8:00 AM (before dosing) and at 4:00 PM on days 2, 3 and 5. Additional blood samples were taken on day 4 and day 6 at 8:00 AM. Using a questionnaire, subjects were asked whether they had gastrointestinal side effects during the visits. We assessed iron absorption by measuring isotopic enrichment in red blood cells 16 days after administration of the third dose in both supplementation periods. 23 – 25 Hemoglobin (Hb), SHep, iron- and inflammatory biomarkers were measured as described in the Online Supplementary Materials and Methods.