What do the trials say — including the one that changed how everyone should dose it?
Iron's evidence base is a treatment literature (replacement therapy in measured deficiency is among the cleanest interventions in medicine) wrapped around a discovery that recently rewrote its own dosing convention: the alternate-day hepcidin trial. The field also carries the sharpest population-conditional lesson in nutrition: benefit concentrated in the deficient, zero benefit and real risk in the replete. This chapter reads the treatment tier, the dosing science, and the boundaries.
The field with the cleanest treatment tier and the sharpest population rule:
Iron filings in wine treat chlorosis — the empirical cure that worked for the right patients three centuries before hemoglobin was measured (our anemia page's founding story).
Berkeley's isotope studies (Hahn and colleagues) trace dietary iron through the gut wall — the mucosal-regulation era begins, absorption proven to respond to body stores.
Industrial nations fortify staples with iron — population-level deficiency falls quietly, the era's least celebrated mass-health program.
Three groups, studying liver antimicrobial peptides, find the hormone that IS iron regulation — and reveal that iron hiding and infection defense are one system.
Hereditary iron overload is mapped to the hepcidin-pathway defects — the genetic disease understood as a broken gate, transforming diagnosis and family screening.
Stoffel's stable-isotope study: consecutive doses raise hepcidin and close the gate; alternate-day dosing increases fractional absorption — the schedule becomes pharmacology.
Deficiency-without-anemia recognized as its own treatable fatigue entity (our anemia page's case), hepcidin-based therapies emerging, and the test-first rule now gospel across every guideline.
POPULATION · Iron-depleted women, stable-isotope pharmacokinetics, alternating dosing schedules
FINDING · Alternate-day dosing increased fractional and total absorbed iron versus consecutive-day dosing — each 60–120 mg dose raises hepcidin for up to 48 hours, closing the gate against the next dose.
LIMITATION · Short-term pharmacokinetic design; long-term hemoglobin outcomes and real-world adherence differences remain to be confirmed in large trials — the mechanism is solid, the outcome trial is the next step.
POPULATION · Iron-depleted women, consecutive-day versus alternate-day 200 mg dosing
FINDING · Confirmatory evidence: consecutive-day dosing raised hepcidin and reduced absorption; alternate-day maintained the open gate.
LIMITATION · Small sample, pharmacokinetic endpoints — part of the converging hepcidin literature rather than the final word on treatment schedules.
POPULATION · US poison-control and fatality data, children under 6
FINDING · Iron supplements remain a leading cause of fatal pediatric pharmaceutical poisoning — the overdose literature behind the locked-storage rule and unit-dose packaging requirements.
LIMITATION · Surveillance data with improving trends since child-resistant packaging — the persistent finding is the lethality-per-tablet, which is chemistry, not compliance.
POPULATION · Genetic-screening cohorts (European-descent populations)
FINDING · C282Y homozygosity — the classic hemochromatosis genotype — affects roughly 1 in 200–300, with variable but significant iron-overload penetrance: the genetic gate-failure that makes untested supplementation dangerous at population scale.
LIMITATION · Penetrance is incomplete (not every carrier develops overload), and genotype-frequency varies by ancestry — but the prevalence of risk-carriers is high enough that the test-first rule is universal, not cautious.