Although the relationships are not entirely clear, high iron stores may increase the risk of heart disease, cancer (such as breast cancer), and Alzheimer's disease. Similarly, for those with inflammatory bowel disease (Crohn's disease and ulcerative colitis), the areas of the bowel that are inflamed appear to have higher amounts of iron.

There may be a possible connection between iron and these chronic illnesses because iron acts as a pro-oxidant, stimulating the damaging effects in the body of substances known as free radicals.

High levels of iron can come from taking iron supplements or eating too much of foods rich in iron, like red meat. The FDA reports that taking up to 45 mg of iron per day is usually considered safe for the general population.

However, if you have heart disease or you are at particular risk for it (for example, you are a man over age 45, a woman who has gone through menopause, or you have high cholesterol, diabetes, or high blood pressure) and you take a multivitamin, it is best to make sure that there is no more than 9 milligrams of iron per daily dose of the vitamin.