Low iron is one of the most common nutritional deficiencies worldwide, and ferritin is the most sensitive blood marker for detecting it. Yet many people who receive a 'borderline' or 'low' ferritin result are told it's normal because their haemoglobin is fine — a nuance that leads to under-treatment and persistent symptoms.
What ferritin actually measures
Ferritin is an iron-storage protein. Its blood level reflects how much iron your body has in reserve. Unlike serum iron — which fluctuates hour to hour with meals — ferritin gives a stable picture of your iron stores. A low ferritin means your reserves are depleted, even if your red blood cells haven't yet been affected.
Normal reference ranges vary by lab, but a ferritin below 30 µg/L is generally considered low, and below 12 µg/L is severely deficient. Some functional medicine practitioners and sports medicine doctors treat symptoms at levels below 50–70 µg/L, particularly in athletes or women with heavy menstrual cycles.
"You can have iron-deficiency symptoms — fatigue, poor concentration, hair loss — with a normal haemoglobin if your ferritin is depleted. The stores run out before the red cells do."
Dr. Lina Haddad, CMO, Looms
Symptoms of low ferritin
- Persistent fatigue that doesn't improve with sleep
- Hair thinning or increased shedding
- Poor concentration and brain fog
- Cold intolerance and feeling cold when others don't
- Restless leg syndrome, particularly at night
- Reduced exercise tolerance
What to do if your ferritin is low
Iron-rich foods — red meat, lentils, beans, dark leafy greens, fortified cereals — are the first line of response for mild deficiency. Vitamin C taken at the same meal enhances absorption; tea, coffee and calcium-rich foods taken at the same time reduce it. If dietary changes don't raise your ferritin over several months, your doctor may recommend iron supplementation.
Before supplementing, it's worth finding out why your iron is low. Heavy periods, gut malabsorption (coeliac disease, inflammatory bowel disease), and low dietary intake are the most common causes. Treating the underlying cause alongside replenishing stores gives the best long-term outcome.