Carbonyl Iron vs. Ferrous Iron

Carbonyl Iron Less Toxic and Better Tolerated than Ferrous Iron

Slower to Absorb

With ferrous iron, generally all iron is available for absorption. However, with carbonyl iron, only a small percentage is available for absorption.^1,2 The rate at which your body absorbs carbonyl iron depends on the production of gastric acid (which is required to make carbonyl iron soluble), and the balance between the iron being dissolved and absorbed by your intestines. This means that carbonyl iron enters your system much more gradually than other types of iron that can dissolve rapidly.²

Less Toxic than Ferrous Iron

Researchers believe that this slow rate of solubilization minimizes the toxicity of carbonyl iron.¹ In fact, studies have shown that carbonyl iron is far less toxic than other forms of iron, even at high doses. Patients taking carbonyl iron can tolerate 10 to 150 times the standard dose of ferrous sulfate iron, while still having nearly the same side effects.^1,3

Lower Incidence of Overdose

Lower toxicity can also help prevent iron overdose, a serious concern in households with children. Statistics from the American Association of Poison Control Centers show that when compared with ferrous iron, carbonyl iron is associated with a much lower incidence of accidental overdose or poisoning.^4,5 In fact, one study found that between 1985 and 2002, 19 deaths were reported for children who ingested ferrous sulfate, while none were reported for carbonyl iron.⁵