Low iron stores are among the most common reasons people feel worn out. Here’s what the number means, and when to act on it.
Sep 2, 2026
6 min read
Dr. Ines Carvalho
Ferritin is the protein your body stores iron in, and it’s the most useful single number for explaining tiredness with no obvious cause. It drops long before hemoglobin does, which is why a standard complete blood count can look clean while you are running on empty.
Normal is not the same as optimal
Most labs flag ferritin only under 15 or 30 ng/mL. Yet symptoms such as getting winded on stairs, hair shedding, or a heart rate that climbs too fast on easy runs often begin well above that, somewhere below 50. We read against the range where people actually feel well, not where a deficiency becomes impossible to miss.
Why it drops
Periods are the most common cause, followed by low iron in the diet, poor absorption from celiac disease or gastritis, and endurance training, which raises losses and demand together. Ferritin also rises with inflammation, so we read it next to hs-CRP to avoid a falsely reassuring result.
If yours is low, the usual fix is oral iron every other day with vitamin C (daily dosing absorbs worse, not better) and a retest at twelve weeks. If it doesn’t move, that is a finding in itself, and it belongs with your primary care doctor.
Dr. Ines Carvalho
Cardiologist, Tinsdale
