Recommendations generally advise dividing an oral iron dose into twice daily doses to maximize fractional and total iron absorption. However, there is little direct evidence to support this. In short-term studies, the prolonged plasma hepcidin increase after oral iron blunts absorption on the following day; this suggests alternate day dosing may be preferred.We compared iron absorption from: study 1) over three days, consecutive morning doses of 120 mg versus two doses of 60 mg given morning and afternoon; and study 2) doses of 60 mg given every day for 14 days or every other day for 28 days.
60 or 120 mg labeled Fe [54Fe]-, [57Fe]- or [58Fe]-FeSO4 was given as above to fasting iron-depleted women (study 1 and 2: n=20, n=40, respectively). Iron absorption was measured as erythrocyte incorporation of iron stable isotopes.
In study 1, there was no difference in total iron absorption over three days between single and twice daily dosing: geometric mean (-SD, +SD) 40.7 (40.9, 40.6) versus 44.7 (44.8, 44.5) mg, respectively. Fractional iron absorption was not affected by the dosing regimen, but by the day: fractional iron absorption on day 1 was 36-41% higher than on days 2 and 3 (p<0.001). Results from study 2 are being analyzed and will be presented at the conference.
Dividing daily oral iron doses does not significantly increase absorption and often decreases compliance, so it should not be recommended. These studies provide new evidence to optimize oral iron supplementation regimens.