Supplement Label Index

Ferrous Fumarate vs. Ferrous Sulfate

Among 1,931 on-market iron products with an identifiable primary form, 60.8% use Ferrous Fumarate (1,174 products) and 8.2% use Ferrous Sulfate (159).

Ferrous FumarateFerrous Sulfate
Quality tierUnratedTier 2
Iron by weight32.9%20.1%
Share of market60.8%8.2%
On-market products1,174159
Median declared dose18 elemental mg
middle half: 8–26
18 elemental mg
middle half: 11.5–65
Most common brandsDC, Wonder Laboratories, GNC Women's Ultra MegaGeri-Care, Rugby, Major

Doses are declared per serving in elemental mg. “By weight” is the share of the ingredient that is the nutrient itself (e.g. elemental magnesium in a magnesium salt).

Why Ferrous Fumarate is unrated

Widely marketed as comparably bioavailable to ferrous sulfate with less GI upset; in a randomized isotope study (57Fe fumarate vs 58Fe sulfate) absorption did not differ significantly in non-anemic Mexican women (17.5% vs 20.5%), infants (7.0% vs 7.2%) or young children (6.3% vs 5.9%). Usefulness in iron-deficient subjects was not established, so no tier is assigned.

Source: Harrington M et al. 2011, Eur J Clin Nutr 65(1):20-25, PMID 20842166

Why Ferrous Sulfate is tier 2

Reference-standard iron salt used as the comparator in most bioavailability literature; showed lower apparent bioavailability (26.7%) than bisglycinate chelate (90.9%) in one head-to-head 40-child matched-group trial (apparent bioavailability was calculated, not isotope-measured). In a randomized isotope study, ferrous fumarate did not differ significantly from ferrous sulfate in non-anemic women and children.

Source: Pineda O, Ashmead HD. 2001, Nutrition 17(5):381-384, PMID 11377130; Harrington M et al. 2011, PMID 20842166

Tiers summarize published comparative bioavailability or outcome evidence for each form (see methodology). This page describes the market; it is not a recommendation to take either form. Talk to a clinician about what's right for you.

Other iron comparisons