Iron is a very important mineral. Red blood cells in the body contain hemoglobin, a protein that transports oxygen to the cells. Myoglobin performs a similar function for muscle cells. Both hemoglobin and myoglobin contain iron, although most of the iron in the body is found in hemoglobin. Iron supplements are used to prevent or treat iron deficiency and the anemia that may result. There is some indication that iron supplementation may affect blood pressure.

Women are more prone to iron deficiency anemia because of their menstrual periods, but a number of diseases can also cause iron deficiency. Cancer, kidney problems and heart disease have all been found to cause anemia. According to Medline Plus, the Natural Medicines Comprehensive Database has found that iron supplements are effective for anemia caused by chronic disease and iron deficiency anemia.

There is evidence that iron from red meat, which contains what is called heme iron, can increase blood pressure. An article in the July 2008 "British Medical Journal" reported that red meat intake was associated with a higher systolic blood pressure, while iron from vegetable sources, called non-heme iron, resulted in decreased blood pressure. When iron supplements were combined with dietary sources, there was less of an effect on blood pressure.

One study of multimineral supplements that contained iron found blood pressure decreased in the study participants. An article in the 2009 "Asia Pacific Journal of Clinical Nutrition" reported a study in which Chinese women were divided into four groups. One group received high doses and a second group received low doses of multivitamin and multimineral supplements. A third group was given only calcium while a fourth group received a placebo. Blood pressures in the women who took the high-dose multivitamin multimineral supplement were significantly lower than those in the other groups.

Although iron is probably safe when taken in recommended doses, it can have side effects. Iron supplements can cause gastrointestinal complaints such as nausea, abdominal pain, constipation or diarrhea. The data on iron supplementation and blood pressure is both limited and conflicting. There is no evidence to support that taking iron supplements increases blood pressure. In fact, too much iron lowers blood pressure. Medline Plus says that high doses of iron can be dangerous, especially for children, and can cause liver failure, very low blood pressures and even death.