Causes of iron deficiency. Relative prevalence of causes: The predominant mechanism for iron deficiency is blood loss (each mL of blood contains 0·4–0·5 mg of iron). The next major cause is malabsorption of iron. Inadequate intake, in and of itself, is a rare cause of iron deficiency but may compound the effect of blood loss and/or malabsorption. Increased physiological iron needs during life: During pregnancy, iron needs markedly increase from the second trimester to support the 30% expansion of the red blood cell mass (which requires about 450 mg iron in a woman weighing 55 kg). Moreover, the fetus requires about 270 mg iron, which of which is acquired during the third trimester. Inadequate intake: Meat-based heme iron is efficiently absorbed than non-heme iron, thus the propensity for vegetarians and vegans to develop iron deficiency. Malabsorption: Celiac disease can also lead to iron deficiency through gastrointestinal blood loss and malabsorption. The use of proton pump inhibitors or histamine-2 receptor antagonists may lead to iron deficiency from the dose-dependent and duration-dependent inhibitory effect of achlorhydria on iron absorption. Helicobacter pylori may cause iron deficiency through multiple mechanisms, including blood loss and achlorhydria-mediated impairment of iron absorption. Iron deficiency develops in 20% of patients after gastrectomy (for cancer) or gastric bypass surgery (for obesity). Blood loss: The most common source of blood loss is from menstrual periods or from gastrointestinal bleeding (for example, colon cancer, angiodysplasia, colonic polyps, gastritis and peptic ulcer). Additional causes of iron deficiency: Other causes of iron deficiency not shown in the above scheme include chronic hookworm infection and inflammatory bowel disease.
