Ferrous Fumarate
Ferrous Fumarate is a unrated form of Iron, used in 1,180 on-market products and providing 32.9% elemental iron by weight.
1,180
on-market products
unrated
quality tier
32.9%
elemental fraction
Basis: FeC4H2O4, anhydrous (fumarate salts don't commonly form stable hydrates)
Why this tier: Widely marketed as comparably bioavailable to ferrous sulfate with less GI upset, but no comparative human absorption study was independently verified.
Source: uncertain -- needs review