Standard lab panels flag iron deficiency only when hemoglobin falls below anemia threshold. But iron deficiency without anemia — depleted ferritin stores with normal hemoglobin — causes fatigue, cognitive impairment, poor exercise tolerance, hair loss, and restless leg syndrome that can persist for years before anemia develops. A serum ferritin below 30 ng/mL warrants attention even if the CBC is normal.
Iron deficiency is the most prevalent nutritional deficiency globally — affecting an estimated 2 billion people. In developed countries, it disproportionately affects menstruating women (30%+ have suboptimal ferritin), pregnant women, endurance athletes (particularly female runners), vegetarians and vegans, and frequent blood donors. The gap between "not anemic" and "iron replete" is where most functional symptoms live.
| Ferritin Level | Status | Symptoms | Action |
|---|---|---|---|
| <12 ng/mL | Depleted stores — often anemic | Severe fatigue, pallor, shortness of breath, palpitations | Physician evaluation; likely IV iron or high-dose oral |
| 12–30 ng/mL | Iron deficient, pre-anemia | Fatigue, cognitive fog, poor exercise tolerance, hair loss, restless legs | Iron supplementation + dietary optimization |
| 30–70 ng/mL | Low-normal | Subclinical — may have mild symptoms especially in athletes | Dietary optimization; supplementation if symptomatic |
| 70–150 ng/mL | Optimal for most adults | None | Maintain with diet |
| >200 ng/mL | Elevated — investigate | May indicate hemochromatosis, liver disease, or inflammation | Physician evaluation required |
Note: Ferritin is an acute phase reactant — it rises during infection or inflammation. A "normal" ferritin during illness may mask true deficiency. Recheck after illness resolves.
Bioavailability: ~90% relative to ferrous sulfate, with dramatically fewer GI side effects. Iron chelated to two glycine molecules. Absorbed via a different intestinal pathway than inorganic iron — less dependent on stomach acid, less disruptive to gut bacteria, significantly less constipation and nausea. Standard dose: 25–50mg elemental iron daily or every other day. Sold as Gentle Iron, Ferrochel, and various chelated iron supplements. The best first-choice form for anyone with GI sensitivity or who has stopped taking iron supplements due to side effects.
The most common prescription form; good bioavailability (~20% of elemental dose), but constipation and nausea are common. 325mg ferrous sulfate tablet contains 65mg elemental iron. GI side effects are dose-dependent — taking every other day (alternate-day dosing) significantly reduces side effects while maintaining total iron absorption due to hepcidin dynamics. Every other day = less hepcidin suppression between doses = better absorption per dose.
Lower elemental iron content per tablet than ferrous sulfate (ferrous gluconate: ~12% elemental; fumarate: ~33%), requiring more tablets for equivalent dosing. Slightly better GI tolerability than sulfate. Reasonable choices; bisglycinate is still preferred for tolerability.
Take with vitamin C (250–500mg): Ascorbic acid reduces ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), the form absorbed by intestinal receptors. Co-supplementing with vitamin C increases iron absorption 2–3× in controlled studies.
Avoid simultaneous calcium: Calcium directly competes with iron for the DMT-1 transporter. Don't take iron with dairy, calcium supplements, or antacids. Separate by 2+ hours.
Take on empty stomach (if tolerated): Iron absorption is highest in an acid environment — food raises gastric pH and reduces absorption. If GI upset is limiting, take with a small amount of food (not dairy).
Avoid tea, coffee, and phytates around dosing: Tannins (tea, coffee) and phytates (whole grains, legumes) chelate iron and dramatically reduce absorption. Separate iron supplementation from these by 1–2 hours.
Alternate-day dosing: Taking iron every other day (not daily) reduces hepcidin induction — the iron-regulatory hormone that downregulates intestinal absorption after each dose. Studies show equivalent or better total iron repletion with alternate-day vs. daily dosing and fewer side effects.
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