Top 5 Causes of Iron Deficiency

1Chronic Blood Loss (Gastrointestinal and Menstrual)

Blood loss is the most common cause of iron deficiency in adults, particularly in men and postmenopausal women. The body has no physiologic mechanism to excrete excess iron; instead, iron balance is maintained through controlled intestinal absorption. Once iron is lost through bleeding, it must be replaced through dietary intake or supplementation.

Menstrual Bleeding in Premenopausal Women

In premenopausal women, cumulative menstrual blood loss is the leading cause of iron deficiency. Normal menstrual cycles result in approximately 1 mg of iron loss per cycle, while women with menorrhagia (heavy menstrual bleeding) lose 5 to 6 times more iron per cycle, significantly accelerating iron store depletion. The prevalence of iron deficiency in women aged 18-50 years reaches 34%, reflecting the substantial impact of menstrual blood loss on iron status.

Gastrointestinal Bleeding

In men and postmenopausal women, chronic occult gastrointestinal bleeding is the most frequent source of blood loss leading to iron deficiency. Common causes include:

• Peptic ulcer disease
• Vascular ectasias (angiodysplasia)
• Colonic polyps
• Gastrointestinal malignancy (iron deficiency anemia is often the presenting sign of occult GI cancer)
• Inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• Chronic use of aspirin or NSAIDs

Each milliliter of blood lost contains approximately 0.5 mg of iron. Chronic, often occult (hidden), bleeding depletes iron reserves over time.

2Decreased Iron Absorption (Malabsorption)

Malabsorption syndromes represent a significant cause of iron deficiency, despite adequate or even excessive dietary iron intake. The gastrointestinal tract, particularly the proximal duodenum, is the primary site of iron absorption, where both heme iron (from animal sources) and nonheme iron (from plant sources) are absorbed.

Celiac Disease

Celiac disease stands out as the most common gastrointestinal cause of iron deficiency anemia. This autoimmune condition targeting the small intestine causes extensive mucosal atrophy and damage primarily in the proximal duodenum, the critical site for iron absorption. The resulting intestinal mucosal damage reduces absorptive surface area and impairs the expression of iron regulatory proteins.

Interestingly, iron deficiency anemia may be the presenting clinical feature of celiac disease, sometimes occurring in the absence of classic gastrointestinal symptoms such as diarrhea or weight loss. The prevalence of iron deficiency anemia in newly diagnosed celiac disease ranges from 12% to 82% depending on the diagnostic criteria and population studied.

Other Malabsorption Conditions

• Bariatric surgery (particularly gastric bypass/Roux-en-Y)
• Inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• H. pylori infection
• Atrophic gastritis and achlorhydria (reduced stomach acid)
• Short bowel syndrome
• Rare genetic conditions such as iron-refractory iron deficiency anemia (IRIDA)

3Inadequate Dietary Iron Intake

While iron deficiency from purely dietary causes is uncommon in developed nations due to iron fortification of many foods, inadequate dietary iron intake remains a significant cause globally and in specific population subgroups.

In the United States, anemia rarely results exclusively from consuming insufficient iron in the diet. However, certain populations with restricted diets face substantial risk:

• Vegetarians and vegans who do not replace meat with other iron-rich foods have significantly elevated iron deficiency risk, as plant-based (nonheme) iron is absorbed less efficiently than animal-based (heme) iron
• Young children consuming excessive cow's milk are at particular risk, as dairy products are low in iron and can interfere with iron absorption
• People on restrictive diets for weight loss
• Individuals with limited access to fresh, nutrient-dense foods ("food deserts")
• Elderly individuals with poor dietary diversity
• Those with eating disorders

4Increased Iron Requirements (Pregnancy, Lactation, and Rapid Growth)

Pregnancy represents a state of dramatically increased iron demand. More than one-third of pregnant women will experience anemia or iron deficiency during pregnancy, with rates approaching 80% in low- and middle-income countries and 45% in well-resourced countries. Some studies report that 84% of pregnant women experience iron deficiency during the third trimester.

Pregnancy Iron Demands

Pregnancy increases maternal iron demand for three critical reasons:

1. Expansion of maternal plasma and blood volume
2. Fetal requirements for iron in its own hemoglobin and endogenous iron stores
3. Placental iron requirements

The total iron requirements of pregnancy average approximately 1,040 mg, with 270-300 mg transferred to the fetus, 50-100 mg incorporated into the placenta, 250 mg lost at delivery, 450 mg used for maternal red blood cell mass expansion, and 240 mg lost through basal body losses. These large iron demands are concentrated in the last two trimesters, equivalent to approximately 6 mg of absorbed iron per day.

Rapidly Growing Infants and Adolescents

Children during periods of rapid growth represent a second high-risk group, particularly infants born prematurely or with low birth weight, toddlers, and adolescents undergoing pubertal development. Iron requirements increase 2-3 fold from the preadolescent level to 1.37-1.88 mg/day in adolescent boys and 1.40-3.27 mg/day in adolescent girls.

Faster-growing children are paradoxically more likely to become iron deficient because dietary iron availability cannot compensate for increased iron incorporation into growing tissues, myoglobin in expanding muscle mass, and hemoglobin in increased blood volume. In girls, this increased requirement is further compounded by the onset of menstruation, making adolescent females particularly vulnerable to iron deficiency.

5Chronic Kidney Disease, Dialysis, and Functional Iron Deficiency

Patients with chronic kidney disease, particularly those undergoing hemodialysis, experience high prevalence of iron deficiency anemia due to multiple mechanisms. These include reduced erythropoiesis (red blood cell production), blood loss during dialysis procedures, and impaired iron metabolism. The prevalence of iron deficiency in heart failure patients ranges from 37-75.3%, reflecting the substantial burden in this high-risk population.

Anemia of Inflammation (Functional Iron Deficiency)

Also known as anemia of chronic disease, this is a complex cause where iron is present but sequestered and unavailable for red blood cell production. Inflammatory cytokines, especially hepcidin (the master iron regulatory hormone), increase in response to chronic disease. Hepcidin blocks intestinal iron absorption and traps iron within storage cells (macrophages), creating a functional iron deficit despite normal or elevated iron stores.

Associated conditions include:

• Chronic kidney disease and dialysis
• Heart failure
• Autoimmune disorders (rheumatoid arthritis, lupus)
• Chronic infections
• Malignancies

Women of Reproductive Age

• Premenopausal women with normal or heavy menstrual periods
• Pregnant women (>1 in 3 affected)
• Breastfeeding women (increased requirements during lactation)
• Women with menorrhagia or bleeding disorders (von Willebrand disease, other coagulopathies)

Children and Adolescents

• Premature infants and low birth-weight newborns
• Toddlers and preschool children (ages 1-5 years)
• Adolescents undergoing rapid pubertal growth (especially females)
• Children consuming excessive cow's milk
• Picky eaters with limited dietary diversity

Medical and Lifestyle Risk Groups

• Patients with celiac disease, inflammatory bowel disease, or after bariatric surgery
• Patients on chronic NSAID or aspirin therapy
• Dialysis-dependent patients with chronic kidney disease
• Vegetarians and vegans not replacing meat with iron-rich alternatives
• High-performance and endurance athletes (particularly female athletes, with 35% experiencing iron deficiency vs. 5% of general population)
• Regular blood donors
• People living in food deserts with limited access to nutrient-dense foods