@honour.health: Non-heme iron supplements, which are your plant-based iron supplements (like iron glycinate / iron bisglycinate), benefit from vitamin C being in the formula because vitamin C can support the absorption of iron. Adding vitamin C really only benefits plant-based iron supplements. If you're taking an animal-based iron supplement, like one made from heart, liver or other organs, then there's no need to look for a pairing of vitamin C.