EggsStudies show that just one egg can cut iron absorption from a meal by about 27% . (This is just a concern with egg protein; other animal sources can enhance iron absorption.) Vitamin C boosts acidity in the stomach, facilitating iron absorption from a supplement or meal . The likely reasons: Taking iron supplements daily boosts hepcidin , which can block the release of iron into the bloodstream. Ferrous iron (ferrous fumarate, ferrous gluconate, and ferrous sulfate) tends to be inexpensive but can cause upset stomach, nausea, constipation, and diarrhea.