Does ferrous fumarate increase iron levels? Ferrous fumarate, with a dosage of 210 mg, contains 0.1 n of ferrous ammonium sulfate and ferrous gluconate, which can have side effects. Specifically, ferrous fumarate provides 200 mg of the compound and delivers 66 mg of iron. When considering dietary supplements, it’s important to compare options such as calcium and calcium citrate. Many people wonder: which is better, calcium or calcium citrate? This question arises frequently among those looking to boost their nutrient intake. Ultimately, the choice between these two forms of calcium may depend on individual health needs and preferences.