Taking oral iron in the morning with vitamin C and without coffee or other food maximised iron absorption.

Although iron deficiency is a common haematological disorder, our understanding of factors affecting absorption of oral iron supplements is incomplete. Researchers studied the fractional absorption of iron from oral iron supplements administered under six different conditions in 34 healthy, nonanaemic, iron-deficient females (median age, 28 years), each of whom served as her own control. The conditions were separated by at least several days, and in each, the oral supplements contained 100mg of radiolabelled ferrous fumarate.

Compared with the control condition – overnight fasting followed by a morning iron dose taken with water three hours before coffee or breakfast – a morning dose taken with either 80 mg or 500 mg of ascorbic acid significantly improved iron absorption by about 30%. The higher dose did not yield significantly higher absorption. All other strategies reduced iron absorption: afternoon dosing by 37%; co-administration with coffee in the morning by 54%; administration in the morning with coffee, 90 mg of ascorbic acid and food by 66%.

Comment: Taking iron in the morning with an 80 mg-serving of ascorbic acid (the amount in 8 ounces [237 mL] of orange juice) optimised iron absorption in this study. Delaying coffee and breakfast as long as possible after iron ingestion should be recommended, although the three-hour delay studied here may not be feasible for many people. Finally, these researchers have also shown that taking iron every other day results in overall greater absorption than daily dosing (NEJM JW Gen Med Dec 1 2017 and Lancet Haematol 2017; 4: e524-e533).

Marie Claire O’Dwyer, MB BCh BAO, MPH, Clinical Assistant Professor in Family Medicine, University of Michigan Medical School, Ann Arbor, USA.

von Siebenthal HK, et al. Effect of dietary factors and time of day on iron absorption from oral iron supplements in iron deficient women. Am J Hematol 2023; 98: 1356-1363.

Powers JM, Auerbach M. When taking iron, a glass of orange juice a day keeps anemia away. Am J Hematol 2023; 98: 1354-1355.

This summary is taken from the following Journal Watch titles: General Medicine, Oncology and Hematology, Ambulatory Medicine, Hospital Medicine.