Ferritin and Iron Studies
Ferritin and iron studies measure the body's iron stores - and people with obesity, and anyone who has had bariatric surgery, are prone to low iron even when their diet looks adequate.
Plain English
Patient-Friendly Explanation
Ferritin is a protein inside cells that stores iron, and the amount in the blood is a good, if imperfect, reflection of how much iron your body has in reserve. Iron studies usually include ferritin together with serum iron and the total iron-binding capacity, from which transferrin saturation is calculated. Iron deficiency matters because iron carries oxygen: when stores fall you can feel tired, breathless on stairs and mentally foggy, feel the cold more, and notice hair thinning or brittle nails. Restless legs at night and unusual cravings for ice or starch can also appear. Two things make iron deficiency common in the people we see. First, obesity is inflammatory at a low level: inflammation raises a hormone called hepcidin, which blocks iron absorption from the gut and locks iron inside storage cells, so intake can be perfectly adequate and stores still fall. Second, after bariatric surgery the duodenum - where most iron is absorbed - is bypassed or the stomach makes less acid, and iron-rich foods are often eaten less. Ferritin has one important quirk: it rises with inflammation, infection and liver fat, so a normal-looking ferritin in someone with obesity can still hide low iron. A ferritin below 30 means deficiency, and when inflammation is present we read it alongside transferrin saturation and C-reactive protein. Treatment is straightforward once identified: iron tablets taken on alternate days absorb better than daily dosing, ideally with vitamin C and away from tea, coffee, calcium and antacids, with intravenous iron when absorption is poor or stores need rapid correction.
Medical
Clinical Definition
Iron status is assessed with serum ferritin, serum iron, total iron-binding capacity and transferrin saturation; ferritin is the most useful single test but behaves as an acute-phase reactant, rising with inflammation, and is therefore unreliable in isolation when C-reactive protein is elevated. Obesity-associated iron deficiency is well described in adults, adolescents and children, with prevalence estimates from NHANES and other cohorts showing roughly two-fold higher odds of iron deficiency in obesity, driven by hepcidin-mediated sequestration rather than inadequate intake. Interleukin-6 from adipose tissue induces hepatic hepcidin, which binds ferroportin on enterocytes and macrophages, blocking absorption and release of stored iron and producing a functional deficiency with reduced transferrin saturation. Suggested interpretation thresholds: ferritin below 30 micrograms per litre indicates iron deficiency; ferritin of 30-100 with transferrin saturation below 20% suggests iron deficiency in the presence of inflammation, the definition used in chronic kidney disease and heart failure; ferritin above 100 with a high CRP requires repeat testing after any inflammatory illness. After bariatric surgery, iron deficiency is among the most common micronutrient complications: the duodenum and proximal jejunum, the principal sites of iron absorption, are bypassed in Roux-en-Y gastric bypass, acid secretion falls and meat intake often declines. Current guidance recommends iron studies before surgery and at routine intervals afterwards - commonly 3, 6 and 12 months, then annually - with women of reproductive age at highest risk. Pharmacologically, alternate-day oral iron dosing (for example 60 mg elemental iron on alternate mornings, fasting) achieves higher fractional absorption than divided daily dosing through hepcidin escape, and separation from calcium, tea, coffee and antacids improves uptake; intravenous iron is indicated for malabsorption, intolerance or the need for rapid repletion. Correcting deficiency improves fatigue and exercise tolerance and should accompany a weight-loss programme rather than being deferred until the weight is lost.
Key Insight
Why It Matters
If you are always tired while dieting, do not assume that is simply what dieting feels like - low iron is common, easy to miss and easy to treat, and the low-grade inflammation of excess weight is itself a common reason for it. We check ferritin rather than guessing, because a normal ferritin in the presence of inflammation can still be misleading. If you have had bariatric surgery, iron and micronutrient checks are part of your long-term follow-up, not a one-off.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: September 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
