Except for the lactic acid bacteria like Lactobacilli, all microbes require iron for growth. Many of them produce special binding proteins to secure iron from their environments. Humans also produce iron-binding proteins which have as their role the capture of free iron so that microbes can't use it. An excess of iron overcomes this protective mechanism and in-creases susceptibility to bacterial infection. The amount of iron needed for optimal health reflects a delicate balance between deficiency and excess.

The best known effect of iron deficiency is anemia, which is the name given to a state in which the number of red blood cells is lower than normal. Anemia is not the same as iron deficiency, however. There are many different causes of anemia, which include folic acid deficiency, vitamin B12 deficiency, disorders of the bone marrow and conditions which increase the rate at which red blood cells are broken down in the spleen. Iron deficiency, when mild, may not produce anemia but may still cause fatigue, im-mune de-fects or fungal infections of skin. There are probably twenty million people in the U.S. who are iron deficient and half of them are not anemic. Wom-en with chronic fatigue and mild iron deficiency who are not anemic improve their energy after taking low doses of iron. Twenty milligrams per day is all that's needed, no more. Low-dose iron supplements can cure people with recurrent boils on the skin, but only if those people have mild iron deficiency. Presumably, correcting iron deficiency improves metabolism and immunity.

It is unfortunate that most commercial iron pills contain sixty to three hundred milligrams of iron, far more than are needed or than can even be absorbed from a single pill. High dose iron supplements, taken orally or by injection, increase susceptibility to bacterial infec-tion. Studies in southeast Asia and in Africa demonstrate that even low-dose iron can be harmful. When Indonesian school children who are not iron deficient take iron pills, they fail to grow normally. When iron supplements are given to Somali nomads or Masai tribes-man, their rate of infection increases, even though their iron deficiency is corrected. The high frequency of negative responses to iron supplements in Africa and Asia may reflect the interaction between iron and zinc.

Iron in food or pills interferes with zinc absorption and supplemental iron can aggravate zinc deficiency. The recommended daily allowance for zinc (RDA) is based on the assumption that forty per cent of the zinc that is swallowed is absorbed into the body. Actually, zinc absorption is only seventeen to thirty-five per cent and depends upon what is eaten along with zinc. Starch and fiber interfere with zinc absorption, as do calcium and iron. Lack of stomach acid, which may be caused by infection or acid-lowering drugs, also interferes with zinc absorption. Zinc deficiency is common in Africa and Asia, where people consume large quantities of milk, which is high in calcium and low in zinc, and of starches and fibres which inter-fere with zinc absorption. Zinc deficiency profoundly depresses immunity and administering iron to a zinc-deficient person is extremely risky. Not only does iron stimulate bacterial growth, but, by aggravat-ing zinc deficiency, it weakens the immune system of the person being supplemented.

No one should ever take iron supplements unless iron deficiency is present, with the possible exception of pregnant women. The best test for iron deficiency is a blood test called the serum ferritin level. Ferritin is a protein that carries iron, and low ferritin levels are a common sign of iron deficiency. Like all laboratory tests, the interpretation of ferritin levels is subject to interpretation. Because the body has a limited capaci-ty for iron absorption, it does not make any sense to administer more than twenty milligrams of elemental iron at a time. Iron should not be taken as part of a multivitamin or multimineral preparation. Iron interferes with the absorption of the essen-tial minerals zinc, manganese and molybdenum; it destroys vitamin E; its own absorption is blocked by calcium and magnesium. Iron is best absorbed after a meal, with a small quantity of vitamin C (between one hundred and five hundred milligrams).