Myoglobin is similar to hemoglobin in that it is an iron-protein compound that holds oxygen and carries it into the muscles, mainly the skeletal muscles and the heart. It provides our ability to work by increasing oxygen to our muscles with increased activity. Myoglobin also acts as an oxygen reservoir in the muscle cells. So muscle performance actually depends on this function of iron, besides the basic oxygenation by hemoglobin through normal blood circulation.
Foods Most Concentrated in Iron*
|Mgs. Iron/100 g.**
|| Edible Food
||Mgs. Iron/100 g.**
|| Edible Food|
|14.9||wheat bran||2.7|| cooked soybeans|
|10.5||sesame seeds, whole||2.3|| eggs |
|3.9||dried prunes||1.5|| chicken |
|3.7||lean beef||1.3||mung bean sprouts|
||1.1||whole wheat bread|
|3.2|| Swiss chard|
*From The Nutrient Content of Foods (Mineralab, Hayward, CA, 1979)
**About 4 oz.
Hemoglobin—and therefore iron—really does give us our strength and the look of good health—our "rosy cheeks." One of the first symptoms of low iron is weakness, fatigue, or loss of stamina. Anemia results only after longer deficiency of iron or other nutrients; then, less hemoglobin and usually fewer red blood cells are made, and our ability to carry oxygen through the body is diminished. Iron and hemoglobin improve our respiratory activity. Many of the oxygen-dependent diseases (diseases that have symptoms based on circulation and the delivery of oxygen to tissues), such as coronary artery disease and vascular insufficiency, are worsened with iron deficiency. Many other symptoms, both psychological and physical, occur when we do not have enough iron. On the other hand, Jerome Sullivan, a researcher on iron metabolism, has recently shown that excess iron intake and storage may increase our risk of atherosclerosis and heart disease.
Iron is needed by some important enzymes for energy production and protein metabolism. The cytochrome system (a class of protein molecules that play a role in oxidative processes) depends on iron enzymes, which may work within the mitochondria (energy factories) of the cells to produce energy. The iron cytochromes, iron catalase, and iron peroxidase probably help protect our tissues and cells from oxidative damage, although most of the research in this area has been done on animals, and it is not clear yet whether the findings are analogous in humans, or if, in fact, iron can be an irritant to the vascular lining. Research is also being done on iron's role in the formation and health of tissue collagen and elastin and the involvement of iron in the immune system's health. When iron in the body is low, there seems to be an increased incidence of infections, possibly because of a decrease in lymphocyte proliferation and other white blood cells' ability to kill microorganisms. Iron also is helpful in the production of carnitine, a nonessential amino acid important for the oxidation and utilization of fatty acids.
Uses: Of course, the main use of iron is in the prevention and treatment of iron deficiency and iron deficiency anemia, whether caused by blood loss, pregnancy, or a low-iron diet. When total body iron or circulating iron is low, fatigue, learning difficulties, irritability, and other subtle symptoms may occur long before actual anemia is seen. Many emotional symptoms may occur in children as well.
Iron is used routinely during pregnancy and breastfeeding to prevent iron deficiency. Because of increased iron needs during these times, it is difficult to obtain all the required iron from the diet alone. The infant will usually get enough iron but will pull stores from the mother, who could become very depleted. Also, whenever there are menstrual periods with more than normal amounts of bleeding (medically called menorrhagia), iron is often suggested as a regular supplement. Iron has also been helpful in reducing pain in some women who have painful menstrual periods.
Sometimes fatigue, especially muscle fatigue and poor physical stamina, will respond to iron supplements. Subtle oxygen-deficit respiratory problems may be helped by attaining adequate iron levels, probably because the iron provides increased hemoglobin production and improved oxygenation of the tissue. There is some question as to whether iron acts as a mild antioxidant, protecting the cells and tissues from oxidative damage, or whether it actually stimulates oxidation and can cause problems.
Deficiency and toxicity: There is a controversy about iron toxicity-is everyone sensitive to iron overload from supplements, or does it affect only people who are genetically predisposed to iron accumulation and irritation? Iron overload is seen most commonly in older men because they tend to take supplements or iron tonics though losses may be small and through the years tend to accumulate iron stores, primarily in the liver. Usually, it takes moderately high amounts over a long period with minimal losses of this mineral to develop any iron toxicity problems. Further research by Jerome Sullivan suggests that iron overload is a factor in the development of atherosclerosis. A high-meat diet, separate iron supplements, or even the extra 18 mg. of iron that is contained in the average RDA-type multivitamin is more than many people, particularly men, require. Men lose very little iron, since the body recycles most of it; their needs are only about 10 mg. daily. Consuming much more than this may increase the risk of atherosclerosis and heart disease by an as-yet-undetermined mechanism, possibly through increased oxidation and free-radical formation. Women in the menstruating years seem to be protected from this increased risk, though they lose this protection after menopause, when their risk of heart disease rises to a level close to men's.
Children have been known to develop acute toxicity from eating extra vitamins or finding some of mother's ferrous sulfate or other iron supplement. Each year there are about ten deaths reported of young children who eat more than ten 300 mg. iron tablets-that is, more than 3 grams of iron-at one time.
It is unlikely that one would develop any iron toxicity from dietary sources alone, even with 50-75 mg. per day intake, unless all food is prepared in iron cookware, as is done in some African tribes, or unless the genetic iron storage disease called hemochromatosis is present. If this disease occurs, tissue damage may result from iron deposits in the liver, pancreas, spleen, skin, or heart. These iron deposits can cause cirrhosis of the liver, fibrosis of other tissues, a bronze color to the skin, and diabetes due to pancreatic disease, as well as joint problems or cardiac insufficiency. Hemochromatosis, a genetic metabolism problem that probably affects the regulation of iron absorption, can be discovered through blood tests and occurs in about 1 person in 20,000. Treatment includes a low-iron diet, avoidance of iron supplements, and giving regular donations of blood so that the iron stores will be used to make new red blood cells.
The term for excess iron storage in the body is hemosiderosis, or siderosis. Here an amorphous brown pigment called hemosiderin (about 35 percent iron as ferric hydroxide) is deposited in the liver and other tissues, which is not usually a problem unless there are excessive amounts. These increased iron stores usually come not from diet but from iron supplements or blood transfusions. Symptoms of iron toxicity include fatigue, anorexia, weight loss, headaches, dizziness, nausea, vomiting, shortness of breath, and a grayish hue to the skin. Iron has been found in increased levels in joints of patients with rheumatoid arthritis and may contribute to inflammation through increased hydroxyl free radicals. Supplementation should be avoided by patients with arthritis unless a proven iron deficiency is present.