What to Know About Iron Deficiency

Iron deficiency is a lack of usable iron in the body, and it is the leading nutritional deficiency globally: the World Health Organization's most recent global estimates, from 2019, put anemia — a condition iron deficiency commonly causes — at roughly 30 percent of women aged 15 to 49 and 37 percent of pregnant women worldwide. In its early stages it often produces no symptoms at all, per the National Heart, Lung, and Blood Institute's published overview. This article publishes information, not medical advice, and anyone with symptoms should see a clinician.

What is iron deficiency, and how does it differ from anemia?

Iron deficiency is a depletion of the body's iron stores; anemia is a shortage of healthy red blood cells or hemoglobin. The two overlap heavily but are not the same: iron deficiency can exist without anemia, a stage sometimes called non-anemic iron deficiency, and anemia has causes unrelated to iron, including vitamin B12 deficiency and chronic disease. Hemoglobin is the iron-containing protein that carries oxygen in the blood, which is why depleted iron eventually shows up as fatigue and breathlessness. The distinction matters clinically, and it is why a clinician orders specific tests rather than assuming.

What are the symptoms of iron deficiency?

Common symptoms, per the NHLBI's overview and the American Society of Hematology's patient materials, include tiredness, weakness, pale or sallow skin, shortness of breath, dizziness, cold hands and feet, and unusual cravings for ice or dirt — a phenomenon called pica. Brittle nails and hair thinning appear on both organizations' symptom lists. Because early deficiency is often silent, the absence of symptoms does not rule out depletion; the WHO's global estimates imply that hundreds of millions of people with anemia are undiagnosed.

Who is most at risk?

The documented risk groups are consistent across the CDC's and the WHO's published materials: women with heavy menstrual periods, pregnant women — whose iron needs rise with blood volume expansion — infants and young children with rapid growth, people with gastrointestinal conditions like celiac disease or inflammatory bowel disease that impair absorption, and people with chronic blood loss, including from regular blood donation. Vegetarians and vegans are listed by the ASH as a moderate-risk group because plant iron is absorbed less efficiently than heme iron from meat.

How is it diagnosed and measured?

By blood tests, in a documented sequence. A clinician typically starts with a complete blood count, which measures hemoglobin, and follows with iron studies: serum ferritin, which reflects stored iron and is generally the first value to fall; serum iron; transferrin saturation; and total iron-binding capacity. Ferritin is the standard early marker, per the ASH's diagnostic materials — though ferritin rises with inflammation, which clinicians account for when interpreting results in people with infection or chronic inflammatory conditions. No self-test substitutes for this panel.

What does the evidence say about screening and supplementation?

Guidance differs by body and population, and the differences are worth seeing side by side:

Daily oral iron supplementation for iron-deficiency anemia is standard clinical practice supported by randomized evidence; the evidence for routine supplementation or screening in asymptomatic populations is what remains unsettled, as the USPSTF's insufficient-evidence ratings state plainly.

What remains uncertain?

The optimal screening strategy for people without symptoms, the best dosing schedule — some trials suggest alternate-day dosing absorbs better than daily, a finding from pharmacokinetic studies that guidelines have not fully absorbed — and the long-term effects of supplementation in non-anemic deficiency. These are open research questions, and current guidance reflects that openness.

When should someone see a clinician?

Persistent fatigue, unexplained breathlessness, pale skin, or unusual cravings warrant a routine appointment and blood work. Certain signs warrant urgent care: chest pain, fainting, rapid heartbeat, black or tarry stools, or vomiting blood, which the NHLBI's materials list as indicators of possible severe anemia or bleeding. Anyone with a known condition that impairs iron absorption should discuss monitoring with their clinician rather than self-supplementing, since excess iron carries its own harms.