Iron deficiency, or sideropenia, is the state in which a body lacks enough iron to supply its needs. Iron is present in all cells in the human body and has several vital functions, such as carrying oxygen to the tissues from the lungs as a key component of the hemoglobin protein, acting as a transport medium for electrons within the cells in the form of cytochromes, and facilitating oxygen enzyme reactions in various tissues. Too little iron can interfere with these vital functions and lead to morbidity and death.Total body iron averages approximately 3.8 g in men and 2.3 g in women. In blood plasma, iron is carried tightly bound to the protein transferrin. There are several mechanisms that control iron metabolism and safeguard against iron deficiency. The main regulatory mechanism is situated in the gastrointestinal tract. The majority of iron absorption occurs in the duodenum, the first section of the small intestine. A number of dietary factors may affect iron absorption. When loss of iron is not sufficiently compensated by intake of iron from the diet, a state of iron deficiency develops over time. When this state is uncorrected, it leads to iron-deficiency anemia, a common type of anemia. Before anemia occurs, the medical condition of iron deficiency without anemia is called latent iron deficiency (LID). Anemia is a condition characterized by inadequate red blood cells (erythrocytes) or hemoglobin. When the body lacks sufficient amounts of iron, production of the protein hemoglobin is reduced.
Sometimes transfusions are considered for people who have chronic iron deficiency or who will soon go to surgery, but even if such people have low hemoglobin, they should be given oral treatment or intravenous iron. Intravenous iron therapy for non-anaemic, iron-deficient adultsCurrent evidence is limited to base any recommendations that intravenous iron therapy is beneficial for treating non-anaemic, iron-deficient adults. Further research in this area is needed as current body of evidence is very low quality. Cancer research
The presence of Helicobacter pylori in the stomach can cause inflammation and can lower the threshold for the development of gastric cancer. In the setting of iron deficiency, H. pylori causes more severe inflammation and the development of premalignant lesions. This inflammatory effect appears to be mediated, in part, through altered bile acid production including an increase in deoxycholic acid, a secondary bile acid implicated in colon cancer and other gastrointestinal cancers. See also
Bahima disease
CO2 fertilization effect

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Further reading
. Zeglam A, Abugrara A, Kabuka M. Autosomal-recessive iron deficiency anemia, dystonia and hypermanganesemia caused by new variant mutation of the manganese transporter gene SLC39A14. Acta Neurol Belg. 2019 Sep;119(3):379-384. doi: 10.1007/s13760-018-1024-7. Epub 2018 Sep 19. PMID 30232769. External links

"Recommendations to Prevent and Control Iron Deficiency in the United States". U.S. Centers for Disease Control and Prevention. "Advice for Improving your Iron Intake" (PDF). University of South Hampton, NHS Foundation Trust. Archived from the original (PDF) on 29 November 2015.