rarely, laryngological bleeding or from the respiratory tract
inadequate intake (see below)
substances (in diet or drugs) interfering with iron absorption
Fluoroquinolone antibiotics
malabsorption syndromes
inflammation where it is adaptive to limit bacterial growth in infection, but is also present in many other chronic diseases such as Inflammatory bowel disease and rheumatoid arthritis
parasitic infectionThough genetic defects causing iron deficiency have been studied in rodents, there are no known genetic disorders of human iron metabolism that directly cause iron deficiency. Athletics
Possible reasons that athletics may contribute to lower iron levels includes mechanical hemolysis (destruction of red blood cells from physical impact), loss of iron through sweat and urine, gastrointestinal blood loss, and haematuria (presence of blood in urine). Although small amounts of iron are excreted in sweat and urine, these losses can generally be seen as insignificant even with increased sweat and urine production, especially considering that athletes bodies appear to become conditioned to retain iron better. Mechanical hemolysis is most likely to occur in high-impact sports, especially among long-distance runners who experience "foot-strike hemolysis" from the repeated impact of their feet with the ground. Exercise-induced gastrointestinal bleeding is most likely to occur in endurance athletes. Haematuria in athletes is most likely to occur in those that undergo repetitive impacts on the body, particularly affecting the feet (such as running on a hard road, or Kendo) and hands (e.g. Conga or Candombe drumming). Additionally, athletes in sports that emphasize weight loss (e.g.
ballet, gymnastics, marathon running, and cycling) as well as sports that emphasize high-carbohydrate, low-fat diets, may be at an increased risk for iron deficiency. Inadequate intake
A U.S. federal survey of food consumption determined that for women and men over the age of 19, average iron consumption from foods and beverages was 13.1 and 18.0 mg/day, respectively. For women, 16% in the age range 14–50 years consumed less than the Estimated Average Requirement (EAR), for men ages 19 and up, fewer than 3%. Consumption data were updated in a 2014 U.S. government survey and reported that for men and women ages 20 and older the average iron intakes were, respectively, 16.6 and 12.6 mg/day. People in the U.S. usually obtain adequate amounts of iron from their diets. However, subgroups like infants, young children, teenaged girls, pregnant women, and premenopausal women are at risk of obtaining less than the EAR. Socio-economic and racial differences further affect the rates of iron deficiency. Bioavailability
Iron is needed for bacterial growth making its bioavailability an important factor in controlling infection. Blood plasma as a result carries iron tightly bound to transferrin, which is taken up by cells by endocytosing transferrin, thus preventing its access to bacteria. : 30  Between 15 and 20 percent of the protein content in human milk consists of lactoferrin that binds iron. As a comparison, in cows milk, this is only 2 percent. As a result, breast fed babies have fewer infections. Lactoferrin is also concentrated in tears, saliva and at wounds to bind iron to limit bacterial growth.