'Heme' is an iron-containing compound found in a number of important proteins such as hemoglobin and myoglobin, which are involved in the transport and storage of oxygen. While hemoglobin, the primary protein found in red blood cells, transports oxygen from the lungs to body tissues, myoglobin functions in the transport and short-term storage of oxygen in muscle cells, helping to match the supply of oxygen to the demand of working muscles (3, 4). Therefore, the most important effect of an inadequate iron status is an impaired physical performance.
'Cytochromes' are heme-containing compounds that are critical to cellular energy production through their roles as electron carriers in mitochondrial electron transport. Cytochrome P450 is a family of enzymes that functions in the metabolism of a number of important biological molecules, as well as the detoxification and metabolism of drugs and pollutants. Non-heme iron-containing enzymes are also critical to energy metabolism (3).
'Catalase' and 'peroxidases' are heme-containing enzymes that protect cells against potentially damaging highly reactive oxygen species (e.g., H2O2). In addition to such antioxidant effects, heme-containing enzymes can catalyze the production of reactive oxygen species used to kill bacteria, as part of the immune response (3,4).
When cellular oxygen concentration drops below a critical threshold ('hypoxia'), experienced by those who live at high altitudes or those with chronic lung disease, compensatory physiologic responses such as increased red blood cell formation, blood vessel growth, and production of certain enzymes, is induced. The activation of genes, coding for enzymes that play an important role in responses to inadequate oxygen supply, is an iron-dependent process (5, 6).
The European Food Safety Authority (EFSA), which provides scientific advice to assist policy makers, has confirmed that clear health benefits have been established for the dietary intake of iron in contributing to: