Babies are born with iron stored in their bodies but because they grow so fast they need more than what can be stored. Babies between 9 months and two years of age are at the greatest risk for anemia if they are not being breastfed or have natural sources of iron in their diet such as liver, red meat, pork, seafood, beans, and dark leafy greens. Even if they are breastfed, it is important that mom has these foods in her diet for her baby to benefit.
The problem with supplementing with iron-fortified formula, cereal, or vitamins is that the side-effects often can be just as bad if not worse. Constipation is the most common side-effect but occasionally there can be diarrhea and gastrointestinal inflammation. Iron supplements may even be an underlying contributing factor to gut dysbiosis. Too much iron can also be poisonous to children under six years of age.
So what is going on? Why do iron supplements cause constipation and gut inflammation when foods high in iron do not?
Most iron supplements are simple salts like iron fumarate, iron gluconate, or iron sulfate. But iron compounds are not bioavailable in an aerobic environment. So some supplements use chelates like iron bis-glycinate to make the iron more soluble.
Unfortunately, even with these efforts to make iron more bioavailable, the rapid pH changes in the digestive tract (from acidic pH in the stomach to more neutral in the small intestine) will cause the iron to become insoluble. Any iron that isn't absorbed (which can be as much as 70% in some supplements) can cause inflammation in the gut due to a process called redox cycling, which creates free radicals. Any remaining iron travels to the lower bowel where it feeds iron-loving pathogenic bacteria leading to lower levels of beneficial bacteria, constipation, diarrhea and more inflammation.
In contrast, iron found in our diet comes in the form of ferritin, a protein-bound form of tiny iron oxohydroxide particles found in both plant and animal tissue. Ferritin doesn't dissolve in the digestive tract but is absorbed through the gut wall and is carried directly into the cells where the iron is released through enzymatic processes from lysosomes making it available for use by the cell. Ferritin doesn't cause inflammation in the gut and bacteria cannot absorb it the same way so it doesn't have the side effect risk.
That has led some scientists to try and make a better iron supplement called IHAT. In the meantime food sources of iron remain the most effective at reducing iron deficiency anemia with the least harmful side effects.
Recovery from the side effects of iron supplementation should include probiotics, Vitamin C, and food rich in Antioxidants.