What causes low iron and zinc levels in adults, particularly women of childbearing age?

Causes of Low Iron and Zinc Levels

Low iron and zinc levels in women of childbearing age are primarily caused by inadequate dietary intake, menstrual blood loss, and increased physiological demands, with only 25% of women in this age group meeting recommended dietary allowances for iron through diet alone. 1

Primary Causes of Iron Deficiency

Inadequate Intake and Absorption

• Dietary insufficiency is the leading cause, with only one-fourth of adolescent girls and women of childbearing age (12-49 years) meeting the recommended dietary allowance for iron through diet 1
• Low iron bioavailability from plant-based diets, as non-heme iron (from plants) is two to three times less absorbable than heme iron from meat, poultry, and fish 1
• Dietary inhibitors including polyphenols in vegetables, tannins in tea, phytates in bran, and calcium in dairy products reduce iron absorption 1

Increased Losses

• Heavy menstrual blood loss (≥80 mL/month) affects approximately 10% of women of childbearing age in the United States and is the most important risk factor for iron-deficiency anemia 1
• Intrauterine device use is associated with increased menstrual blood loss 1
• Gastrointestinal blood loss from occult bleeding, inflammatory disorders, or bleeding disorders 1

Increased Physiological Demands

• Pregnancy increases iron requirements threefold in the second and third trimesters to approximately 5.0 mg iron/day due to blood volume expansion (35%), fetal growth, and placental development 1
• High parity increases cumulative iron depletion 1
• Adolescence (ages 12-18 years) increases requirements due to rapid growth 1

Medical Conditions

• Malabsorption syndromes including short bowel syndrome, bariatric surgery, inflammatory bowel disease, chronic pancreatitis, and cystic fibrosis 1
• Chronic inflammation can cause anemia that must be differentiated from true iron deficiency 1

Primary Causes of Zinc Deficiency

Inadequate Intake

• Dietary insufficiency from low zinc intake or poorly absorbable zinc sources 1
• Vegetarian and vegan diets due to absence of highly bioavailable animal sources and presence of phytates that inhibit zinc absorption 1
• Eating disorders including anorexia nervosa and bulimia 1

Malabsorption

• Gastrointestinal disorders including short bowel syndrome, bariatric surgery, cystic fibrosis, chronic pancreatitis, and inflammatory bowel disease 1
• Phytate-rich diets that bind zinc and reduce absorption 1
• Genetic disorder: Acrodermatitis enteropathica (autosomal recessive mutation in ZIP4 transporter gene) presents in childhood 1, 2

Increased Losses

• Gastrointestinal losses from enterostomy, enterocutaneous fistula, or chyle leaks 1
• Increased urinary losses in hypercatabolic conditions (burns, trauma, sepsis), renal disease, alcoholism, and with certain medications (diuretics, angiotensin-receptor blockers) 1, 2
• Prolonged renal replacement therapy 1

Increased Requirements

• Infants, children, adolescents, pregnant and lactating women have increased zinc requirements and are at higher risk of depletion 1

Medical Conditions

• Chronic parenteral nutrition without or with low zinc supplementation 1
• Alcoholic cirrhosis and diabetes mellitus 1
• Prolonged complete enteral nutrition 1

Important Interaction: Zinc-Iron Competition

A critical caveat: excess zinc supplementation (22 mg/day) can induce iron deficiency by decreasing plasma ferritin, transferrin saturation, and increasing transferrin receptor levels, even while improving zinc indices. 3 This competitive interaction occurs during intestinal absorption when zinc is taken in supplemental doses, though iron supplementation does not adversely affect zinc status 3, 4

Clinical Approach

For Iron Deficiency

• First, rule out chronic inflammation using transferrin saturation to differentiate iron deficiency anemia from anemia of chronic inflammation 1
• Address underlying inflammation before supplementing with iron if deficiency persists 1
• Investigate gastrointestinal blood loss in patients without obvious causes 1

For Zinc Deficiency

• Recognize that plasma zinc is not a sensitive marker and is highly variable under different conditions 1
• Look for clinical manifestations including growth retardation, increased infections, delayed sexual maturation, eye problems, taste abnormalities (hypogeusia), alopecia, and skin rash 1, 5
• Consider zinc supplementation cautiously in divided doses, as it may worsen iron status if given in excess 1, 3

Key Pitfall to Avoid

Never supplement zinc at doses >25 mg without monitoring iron status, as this can induce cellular iron deficiency and reduce iron absorption, particularly problematic in women of childbearing age already at risk for iron deficiency 3, 4