How long does it take for ferrous fumarate 210mg to start working? When considering ferrous fumarate, it’s important to note that it may vary from person to person. On the other hand, ferrous gluconate, which contains 300mg of elemental iron, is another option for iron supplementation. It’s essential to choose the right supplement for your needs. Additionally, if you’re looking to enhance the absorption of iron, incorporating calcium citrate 500 into your regimen could be beneficial. Remember that calcium citrate 500 can interact with iron supplements, so timing your doses is crucial. Overall, both ferrous fumarate and ferrous gluconate, along with calcium citrate 500, can play a significant role in your iron intake and overall health.