What is p iron? Ferrous fumarate, also known by other names, is a type of iron supplement. Ferrous gluconate, another form of iron, can sometimes cause nausea. Foods rich in iron include options like iron II lactate and ferrous gluconate, which provides 324 mg of iron. Additionally, incorporating sublingual calcium citrate can enhance mineral absorption. It is beneficial to consider sublingual calcium citrate while discussing iron supplements, as it may improve overall nutrient uptake. Thus, when taking ferrous fumarate or ferrous gluconate, pairing them with sublingual calcium citrate may help alleviate potential side effects like nausea.