For confirmed iron deficiency in women, ferrous sulfate is the most studied and lowest-cost oral iron form, while ferrous bisglycinate is often better tolerated. Research supports alternate-day dosing — taking iron every other day rather than daily — because it can result in similar or better total absorption with fewer GI side effects.

Common oral iron forms

• Ferrous sulfate — most studied, inexpensive, can cause GI side effects in some

• Ferrous bisglycinate (chelated iron) — often gentler on the stomach; comparable absorption at appropriate doses

• Ferrous gluconate — lower elemental iron per pill; may be tolerated by those sensitive to higher-dose sulfate

• Heme iron polypeptide — derived from animal sources; less studied

• Iron-rich whole-food blends — useful for maintenance, generally not sufficient for treating diagnosed deficiency

The alternate-day dosing finding

A landmark 2017 study in Lancet Haematology showed that alternate-day dosing can produce greater total iron absorption than daily dosing, because each iron dose temporarily raises hepcidin — a hormone that blocks further iron uptake for ~24 hours (Stoffel et al., Lancet Haematology).

For most women, this means:

• A single dose every other day can be more effective than two daily doses

• Fewer GI side effects (nausea, constipation, dark stools) per absorbed milligram

• Better adherence over the 3–6 months typically needed to rebuild stores

When IV iron is appropriate

If oral iron fails after several months of consistent use, isn't tolerated, or stores are severely depleted, IV iron is an established option. This is a hematology or PCP-led decision.

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How to get more iron from food

Heme iron — found in beef, lamb, chicken thigh, sardines, and oysters — is absorbed more efficiently than non-heme iron from plants. To improve non-heme iron absorption from sources like lentils, tofu, and leafy greens, pair them with vitamin C in the same meal and avoid coffee or tea with iron-rich meals.

Heme vs. non-heme iron

• Heme iron: ~15–35% absorption; found in animal sources

• Non-heme iron: ~2–20% absorption; found in plants and fortified foods; depends heavily on other compounds in the meal

Top iron-rich foods

Heme sources: beef, lamb, chicken thigh and liver, oysters, mussels, sardines, tuna.

Non-heme sources: lentils, chickpeas, white beans, tofu, tempeh, pumpkin seeds, cashews, fortified cereals, spinach, Swiss chard, dark chocolate, dried apricots.

Absorption boosters

• Vitamin C in the same meal — squeezing lemon on greens, citrus alongside lentils, bell pepper with tofu

•  Cooking in cast iron — small but real bumps in acidic, slow-cooked dishes

• Soaking, sprouting, and fermenting grains and legumes — reduces phytates, which limit absorption

Absorption blockers (separate from iron meals)

• Coffee and tea (polyphenols, tannins)

• Calcium supplements and dairy in large amounts

• High-phytate foods without soaking or fermenting

• Certain medications including acid suppressors (PPIs, H2 blockers)