The development of iron deficiency, and the rapidity with which it progresses, is dependent upon the individual's initial iron stores which are, in turn, dependent upon age, sex, rate of growth and the balance between iron absorption and loss. The generally lower value for iron stores in adult women, for example, reflects the composite effect of menstrual losses (approximately 1 mg of iron loss per day), lower caloric intake, use of supplemental iron, and iron losses associated with pregnancy and lactation (about 1000 mg each for pregnancy, delivery, and nursing).
Data from the Third National Health and Nutrition Examination Survey (NHANES III; 1988 to 1994) indicated that iron deficiency anemia was present in 1 to 2 percent of adults (table 1) . Iron deficiency without anemia was more common, occurring in up to 11 percent of women (most often premenopausal) and 4 percent of men. In this survey, the prevalence of iron deficiency anemia was significantly higher in older adults, being between 12 and 17 percent in persons 65 years and older [2,3]. (See "Anemia in the older adult", section on 'Iron deficiency anemia'.)
The major causes, stages, and diagnosis of iron deficiency in adults will be reviewed here. These issues are best understood if the reader first reviews the regulation of normal iron balance. (See "Regulation of iron balance".)
The treatment of iron deficiency and issues concerning iron balance in children and adolescents are discussed separately. (See "Treatment of the adult with iron deficiency anemia" and "Iron deficiency in infants and young children: Screening, prevention, clinical manifestations, and diagnosis" and "Iron requirements and iron deficiency in adolescents".)
CAUSES OF IRON DEFICIENCY
Blood loss — The major cause of iron deficiency in affluent countries is blood loss, either overt or occult . Overt blood loss is, by definition, obvious and not difficult for the clinician to recognize, often by history alone. Examples include severe traumatic hemorrhage, hematemesis, melena, hemoptysis, severe menorrhagia, and gross hematuria.