Inadequate intake, reduced absorption, and chronic blood loss are the primary causes of low iron stores in adults.

Low iron stores, clinically characterized by low serum ferritin levels, are primarily driven by an imbalance where physiological demand exceeds the supply of bioavailable iron. In adults, this imbalance most commonly results from the synergistic or individual effects of inadequate dietary intake, impaired intestinal absorption, or persistent blood loss.

Clinical and Effectiveness Evidence

In clinical practice, low iron stores are the precursor to iron deficiency anemia (IDA). The body maintains a hierarchy of iron use, prioritizing hemoglobin production by depleting ferritin stores in the liver and spleen when external supply falls short.

• Dietary Intake: Research indicates that failing to meet the requirement for bioavailable iron—particularly heme iron from animal sources—is a primary driver of deficiency. Studies show that increasing animal flesh intake (85–300 g/day) is positively correlated with improved iron status.
• Chronic Blood Loss: This is a dominant etiological factor because red blood cells contain roughly 70% of the body's iron. In postmenopausal women and men, gastrointestinal (GI) abnormalities (e.g., peptic ulcers or malignancies) are responsible for approximately one-third of IDA cases. For premenopausal women, menorrhagia (heavy menstrual bleeding) remains the leading cause.
• Absorption: Conditions like celiac disease, which causes duodenal villous atrophy, result in iron deficiency in 12–82% of patients at diagnosis.

Mechanistic Explanations

The depletion of iron stores follows a specific physiological pathway involving the iron exporter ferroportin and the storage protein ferritin.

• Absorption Pathways: Non-heme iron requires an acidic gastric environment to transition from the ferric (Fe³⁺) to the absorbable ferrous (Fe²⁺) state. Atrophic gastritis (AG), which affects up to 47.8% of adults over age 70, causes hypochlorhydria, significantly impairing the solubilization of iron and its uptake via Divalent Metal Transporter 1 (DMT1).
• Storage Depletion: When intake or absorption is insufficient, the body mobilizes ferritin to maintain erythropoiesis (red blood cell production). Only after these stores are exhausted—typically reflected by ferritin levels falling below 30–50 μg/L—does hemoglobin production begin to decline.

Clinical Implications

Because low iron stores are often the first sign of underlying pathology, clinical guidelines from organizations like the British Society of Gastroenterology (BSG) prioritize investigating the source of iron loss.

• Diagnostic Priority: In older adults or postmenopausal women, unexplained low ferritin frequently necessitates a GI tract evaluation to rule out occult bleeding from polyps or colorectal cancer.
• Multifactorial Nature: Iron deficiency in older populations is often a "perfect storm" of reduced gastric acid (often from proton pump inhibitor use), lower dietary diversity, and chronic low-grade inflammation.

Bottom line

The claim is strongly supported by science; inadequate intake, reduced absorption, and chronic blood loss are the three primary and scientifically validated pillars of iron store depletion in adults. Management requires identifying which of these mechanisms is dominant to address the root cause.