A small randomized trial published October 25, 2026 in the European Journal of Nutrition gave women with low iron stores less iron, taken every other day. Over six weeks, ferritin, a blood marker of stored iron, rose in both groups, with no significant difference.
That sounds like a win for every-other-day iron. It isn't that simple. The lower-dose group also got a different form of iron and a daily gut supplement, so the trial cannot say whether the schedule made the difference.
What the study did
The single-center study, from the University of Bologna, randomized 66 women aged 18 to 50 with serum ferritin below 30 ng/mL plus symptoms such as fatigue. All were healthy and of Caucasian ethnicity, and none reported heavy menstrual bleeding (full text).
For 42 days, one group took 21 mg of elemental iron every 48 hours, as micronized, dispersible ferric pyrophosphate, plus a daily "gut microbiota modulator" (BIOintestil, with palmrose oil and ginger rhizome powder). The other group took 30 mg of elemental iron every day as sucrosomial ferric pyrophosphate. The first group got approximately one third of the cumulative iron dose. Both products also contained vitamins and other ingredients, whose effects were not analyzed separately.
What it found
Serum ferritin, the primary outcome, increased significantly in both groups (p < 0.001), with no significant difference between treatments (p = 0.537). Other iron markers moved similarly in both arms.
Hemoglobin didn't change significantly in either group, but the women weren't markedly anemic at the start. Ferritin rose more slowly at first on alternate days: by day 14 the rise only approached significance (p = 0.051).
Side effects were mild and all digestive. Six women on alternate days and five on daily iron reported them; one in each group stopped. No serious adverse events were reported.
What it can't tell you
The design worries me most. The groups differed in schedule, dose, iron form and the gut supplement at once, so the trial can't say which of them explains the result, or show that every-other-day dosing alone works as well as daily dosing.
It's also small and short, and the paper doesn't describe it as blinded. Sixty-four women completed six weeks, with no follow-up. At this size, "no significant difference" does not prove the two work equally well, and the paper does not describe an equivalence or non-inferiority design.
Hepcidin (a liver hormone that limits iron passing from the gut into the blood), gut bacteria and diet were not measured, so the authors cannot show the gut supplement changed gut bacteria or explains the response.
Then there's the money. Diadema Farmaceutici supplied the study products and part of the funding, and one author sits on its board. The first and corresponding authors founded and hold shares in TGD Srl, owner of the BIOintestil patent, though they no longer have active roles.
The authors also say people with iron deficiency anemia may respond differently.
Why every other day?
The idea comes from hepcidin. In a 2015 study of 54 non-anemic young women with low iron, hepcidin was still raised 24 hours after doses of 60 mg or more, and fractional absorption was 35% to 45% lower. In a 2017 open-label trial in 40 iron-depleted women, 60 mg on alternate days for 28 days gave higher cumulative fractional absorption than 60 mg daily for 14 days (21.8% versus 16.3%). A 2020 crossover study in 19 women with iron deficiency anemia found fractional absorption 40–50% higher on the first day and on an alternate day than on a second day in a row.
Better absorption hasn't clearly meant better results. A 2023 double-blind trial in 150 Swiss women found similar ferritin at equal total doses (median 43.8 versus 44.8 μg/L), but fewer digestive side effects with alternate days. A pilot trial in India of 60 women found 60 mg daily for 14 days improved some red blood cell measures more than 120 mg on alternate days.
These studies used 60 mg or more per dose, and the absorption studies used ferrous sulfate, so they say little directly about the new trial's 21 mg and 30 mg products. The new trial did not measure hepcidin.
Pills and drinks that interact with iron
- Levothyroxine. The Synthroid label says patients should not take the tablets within 4 hours of iron and calcium supplements and antacids (levothyroxine and iron).
- Doxycycline. The doxycycline label says iron-containing preparations impair absorption of tetracyclines. Ask your pharmacist about spacing (doxycycline and iron).
- Calcium, coffee and tea. Studies of meals, not pills, found 165 mg of calcium cut iron absorption by 50–60% (1991), a cup of coffee by 39% (1983) and black tea by 79–94% (1999).
Pilora's reminders can put iron and another medicine at separate times.
The bottom line
This small, six-week, industry-linked trial found that one lower-dose, every-other-day iron product, taken with a daily gut supplement, raised ferritin with no significant difference from a different daily product in women with low iron who were not markedly anemic. It doesn't show that taking iron every other day is better or even as good, or that changing your own schedule would help. If you take iron, especially if it was prescribed, you're pregnant or you have anemia, talk to your doctor or pharmacist before changing how much or how often you take it.