Social media has coined a term for it: "ferritin face" — the sallow skin, dark under-eye circles and generally wrecked look that influencers claim signals low iron. It sounds like just another wellness trend, but the underlying issue is real. Iron deficiency is the world's number one nutritional deficiency, and in the United States it affects nearly one in three adults, disproportionately women.

The signs are easy to brush off, especially when you travel a lot. Fatigue, headaches, hair loss, dizziness and shortness of breath all slot neatly into "too much stress, too many flights". In severe cases there are stranger clues: cravings for ice, chalk or paper (a condition called pica), an inflamed tongue or changes to fingernails. Women in their 20s and 30s are particularly likely to be told their exhaustion is just normal life, says Dr Soumya Rangarajan, a Michigan geriatrician who only got her own levels checked after seeing a colleague's posts about the topic.

Here's the catch that trips many people up: the standard blood test measures haemoglobin, not ferritin, the protein that stores iron. That means the test often only flags a problem once your reserves are badly depleted. A ferritin test catches deficiency earlier — generally a reading under 30 nanograms per millilitre counts as deficient, and many doctors argue the cutoff should be 50 for symptomatic people. Draft guidelines from the American Society of Hematology are expected to adopt the higher threshold for those with symptoms or risk factors like heavy periods or pregnancy. The gap matters: at a Singapore running event, 48% of 271 women who described themselves as fit and healthy tested iron deficient when ferritin was measured.

Underlying conditions can also block absorption — coeliac disease, inflammatory bowel disease, H. pylori infection, gastric surgery, and long-term use of acid-reflux medications like omeprazole. Chronic inflammation from autoimmune disease, kidney disease or heart failure raises a hormone called hepcidin that shuts down gut iron absorption entirely, which is why some patients need IV infusions rather than pills.

Treatment is usually simple: oral iron, often one 65-100mg pill every other day, with infusions as a fallback if levels haven't improved after three months. But experts warn against self-medicating on a hunch. Unneeded iron can cause overload, and for people with haemochromatosis — a genetic tendency to absorb too much — supplements can damage the liver, heart and pancreas over time. Get tested first, and ask for a full iron panel, not a single ferritin number.

Diet can help too. Meat and seafood provide heme iron, which the body absorbs more easily than the iron in beans, greens and fortified grains. Pairing plant-based iron with vitamin C — lentils with tomatoes, cereal with berries — boosts uptake, while tea, coffee and dairy within a couple of hours of an iron-rich meal block it. Vegetarians need almost double the daily iron of meat eaters for that reason. If you're constantly wiped out and blaming busy itineraries, it may be worth ruling out iron before you blame the schedule.