Taking iron supplements every day? Your body may actually absorb less

'I never missed a single day — and my body was absorbing less iron?'

Taking iron supplements every day is widely seen as the responsible approach. But research suggests that daily dosing may actually work against you.

When you take an iron supplement, the body releases a hormone called hepcidin to prevent too much iron from entering the bloodstream at once. Hepcidin acts as a gatekeeper, shutting the door on iron absorption in the intestine.

The problem is that once hepcidin begins blocking iron absorption, it can take nearly a full day before the body is ready to absorb iron again. That means the next day's supplement may not be properly absorbed before hepcidin loses its effect.

That is what gave rise to the idea of taking iron supplements every other day. But recent research has produced conflicting results on whether the approach actually works better.

The case for alternate-day iron dosing traces back to a 2017 study from ETH Zurich in Switzerland. Researchers gave iron-deficient women the same total of 14 iron supplement tablets — one group took them daily, the other every other day — and found that the alternate-day group absorbed 34 percent more iron.

Clinical trials in actual anemia patients followed. In a trial published in 2024 in the Indian Journal of Hematology and Blood Transfusion, a research team in India found that among 68 women with anemia, those who took 120 mg of iron every other day showed greater hemoglobin gains after four weeks than those who took 60 mg daily.

A pilot clinical trial published this year in the international journal Clinical Nutrition, however, found the opposite: young women with iron deficiency who took supplements daily showed better blood markers than those on an alternate-day schedule.

A study by a Mexican research team published in July in Frontiers in Nutrition tracked 171 women with iron-deficiency anemia. After three months, the share of patients whose hemoglobin returned to normal was similar — 75.2 percent in the daily group and 71.7 percent in the alternate-day group.

The alternate-day group was in fact nearly twice as likely to switch to iron injections — a more intensive treatment — with 26.8 percent making the switch compared with 13.9 percent in the daily group.

While the optimal dosing schedule remains contested, the evidence that iron supplements work for those who need them is fairly robust.

A research team at the University of Illinois Chicago published findings in June in Sports Medicine, synthesizing results from 42 trials involving women of reproductive age who exercise.

Active women lose iron not only through menstruation but also through sweat and exercise-related tissue damage, and an estimated 15 to 35 percent of female athletes are believed to experience iron deficiency.

When the team analyzed clinical trials specifically using ferrous sulfate — the most commonly used iron supplement — women who took iron supplements saw hemoglobin rise by 0.42 g/dL and ferritin increase by 12.61.

Ferritin is a protein that stores iron in the body, and ferritin levels measured through a blood test indicate how much stored iron remains. By the University of Illinois team's criteria, a ferritin level below 35 signals stage-one iron deficiency, while a level below 20 indicates stage two — stored iron is depleted, even without anemia.

The benefits were greater in those with more severe iron deficiency. Women at stage two saw their ferritin rise by an average of 14.16.

The research team also said timing is worth considering. Hepcidin, which regulates iron absorption, is at its lowest in the morning and can rise up to 2.5 times its baseline level in the three to six hours after exercise.

For people who exercise, the team said taking iron supplements in the morning or within 30 minutes of a morning workout may therefore improve absorption.

Research has also challenged the common assumption that iron supplements are only necessary for those with anemia.

A research team at the University of Lausanne in Switzerland published results in the Canadian Medical Association Journal in 2012 from a clinical trial in which 198 women aged 18 to 53 who experienced unexplained fatigue were given iron supplements. None of the participants met the clinical threshold for anemia, but all had ferritin levels below 50, indicating their iron stores were not adequate.

Women who took 80 mg of iron daily for 12 weeks reported a 47.7 percent reduction in fatigue scores. Those who took a placebo also reported less fatigue — down 28.8 percent — but the improvement was significantly greater in the iron supplement group.

The research team concluded that "women experiencing unexplained fatigue with ferritin levels below 50 should consider iron supplementation."

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