What your ferritin level really says about your energy

Ferritin is the protein your body stores iron in, and it is the single most useful number for explaining tiredness that has no obvious cause. It falls long before haemoglobin does, which is why a standard full blood count can come back clean while you are running on empty.

Normal is not the same as optimal

Most labs flag ferritin only below 15 or 30 ng/mL. But symptoms — breathlessness on stairs, hair shedding, a heart rate that climbs too fast on easy runs — often start well above that, somewhere under 50. We read against the range where people actually feel well, not the range where a deficiency becomes undeniable.

Why it drops

Menstruation is the most common reason, followed by low dietary iron, poor absorption from coeliac disease or gastritis, and endurance training, which raises losses and demand at once. Ferritin also rises with inflammation, so we read it alongside hs-CRP to avoid a falsely reassuring result.

If yours is low, the fix is usually oral iron taken every other day with vitamin C — more frequent dosing absorbs worse, not better — and a retest at twelve weeks. If it does not move, that is a finding in itself, and it belongs with your GP.