TABLE 3.

Iron content and relative bioavailability¹ (RBV) of ferrous sulfate of commonly used oral iron preparations

Iron salt	Elemental iron content (% iron in formulation)	RBV to ferrous sulfate (%)
Ferrous sulfate	20	Reference
Ferrous sulfate (dried)	32.5	100
Ferrous fumarate	33	100
Ferrous gluconate	12	89
Amino acid chelates (e.g., ferrous biglycinate)	20	100
Carbonyl iron	99	5–20
Sugars (saccharides), usually ferric iron	Variable	Variable

¹Estimates of bioavailability of iron compounds are mainly derived from their comparisons at low doses as food fortificants rather than as supplements. Bioavailability data of iron fortificants may not be entirely applicable to oral iron preparations, but it remains the best evidence of relative bioavailability of oral supplements.