When a patient with chronic tuberculosis was found to have iron deficiency anemia, his doctor thought that correcting his anemia would increase his resistance, so he was given iron supplements, and his condition worsened. In fact, not only tuberculosis but also other infectious diseases are often associated with iron deficiency in the blood. Do we really need iron supplementation in this case? In fact, it is an effective defense mechanism of the body against infection, just as fever occurs after infection. Not many people are fully aware of this, so much so that we are undermining it, either intentionally or unintentionally. It is unwise to reduce fever after an infection, and iron supplementation during an infection can have serious consequences as well. It is generally believed that infectious anemia may be related to accelerated destruction of red blood cells in the blood by bacteria and viruses, disturbance of iron metabolism, and temporary suppression of bone marrow hematopoietic function. This is only the customary explanation. The real reason is that the organism, upon receiving the signal of infection, immediately hides the iron in the body and binds it closely with transferrin, which is equivalent to seizing the free iron and tightly regulating it, in order to deprive the bacteria of the supply of iron and eventually starve them to death. The result is iron deficiency anemia. When the infection is controlled and nutrition is enhanced, the anemia will naturally correct and the hematocrit will return to normal levels in a short period of time. Bacteria cannot grow and reproduce without iron, dating back to 3.5 billion years ago when bacteria appeared on the earth. At that time, the earth was full of iron compounds, so much so that the oceans were also rust-colored. Since then, despite geological changes, the dependence of bacteria on iron has remained unchanged. Eggs are a very good example. Eggs are rich in nutrients and bacteria can easily invade through the porous egg shell. But why is it strange that eggs do not break easily? It turns out that although eggs are rich in iron, it is all in the yolk, and the egg white contains 12% of the accompanying albumin, a protein molecule that binds firmly to iron, so that invading bacteria do not get iron. In folklore, egg whites are often used to coat traumatic surfaces to control infection. Breast milk contains 20 percent lactoferrin, another molecule designed to bind iron. Cow’s milk contains only 2% lactoferrin, so breastfed babies are more resistant to disease. Long ago, the Zulus drank a beer brewed in a tin can and they often suffered from severe amoebic liver abscesses. The Maasai tribes were nomadic, drank large amounts of animal milk, were iron deficient, and only 10% of them suffered from amoebic infections. When a portion of the Maasai were given iron supplements, immediately 88% of them developed amebic infections. Malnourished patients, showing a low-protein state, the corresponding transferrin is also reduced, sometimes less than 10% of normal people. If iron is supplemented without transferrin to bind it, there will be a large amount of free iron in the blood, which will likely contribute to a fatal infection – an unfortunate event that has occurred in relief efforts for disaster victims. Somali homeless people received some of the donated food with iron supplementation, and after a month, 38% of them had infections, compared to 8% of those without iron supplementation. When sick, ham and eggs with iron became unpopular, and we preferred only a light diet, which was another way to keep iron out of the germs. Bloodletting, which has been circulating for years and was considered an act of ignorance, now seems to have perhaps some role in reducing iron reserves. The truth about the beneficial effects of iron deficiency on infections was recognized more than thirty years ago, but until now, it has not been taken seriously, so much so that iron supplements are still being recommended; infants and children are still being fed iron-containing formula when infected; and doctors are still aggressively correcting infected patients when they find them to be iron deficient.