Patient Basics: Iron Deficiency

Iron deficiency means your body doesn’t have enough iron. You need iron to make hemoglobin, the protein in red blood cells that carries oxygen. If low iron goes on long enough, it leads to iron deficiency anemia, a low red blood cell count. Treatment means both replacing the iron and finding out why it ran low.

Key points

• Heavy periods, pregnancy, slow bleeding in the gut and poor absorption are the most common causes.
• Tiredness is the main symptom. Others include shortness of breath, headaches, restless legs, brittle nails and craving ice.
• A ferritin blood test is the best single check of your iron stores.
• Iron pills work for most people. Iron given through a vein (IV) helps when pills don’t.
• In men and in women past menopause, unexplained low iron needs a check of the gut for bleeding.

Low iron vs anemia

Iron deficiency happens in stages. First, the iron your body keeps in storage runs low. At this point your hemoglobin can still be normal. Doctors call this iron deficiency without anemia, and it can still cause tiredness, poor focus and restless legs.

If the shortage continues, your body can’t make enough hemoglobin. Red blood cells shrink and lose color, and you have iron deficiency anemia. Not every anemia comes from low iron. Low vitamin B12 or folate, kidney disease, long-term illness and inherited blood conditions can cause it too.

Iron deficiency symptoms

Symptoms often come on so slowly that people get used to them. They include:

• Tiredness, weakness and less stamina
• Shortness of breath or a pounding heart with activity
• Pale skin, or pale skin inside the lower eyelids
• Headaches, dizziness, and cold hands and feet. Some studies also link low iron with migraines, mostly in women.
• Restless legs, an urge to move the legs at night that can make it hard to sleep
• Hair shedding
• Brittle nails, or in long-standing cases, thin nails that curve up like a spoon
• A sore, smooth, red tongue or cracks at the corners of the mouth
• Cravings for ice, clay, dirt or starch (pica)
• Trouble focusing and irritability

In babies and young children, low iron can slow growth and learning. Iron levels are often checked around age 1.

What causes iron deficiency

Blood loss

• Heavy menstrual periods, the most common cause in women before menopause
• Slow bleeding in the stomach or intestines from ulcers, polyps, cancer or inflammatory bowel disease
• Regular use of pain relievers such as ibuprofen, naproxen or aspirin, which can irritate the stomach
• Giving blood often

Higher need

Pregnancy, fast growth in babies and teens, and hard endurance training all raise the amount of iron your body needs.

Too little iron in the diet

This is more likely with a poorly planned vegetarian or vegan diet, or in toddlers who drink a lot of cow’s milk, which is low in iron and can fill them up.

Poor absorption

Celiac disease, weight-loss surgery such as gastric bypass, a stomach infection called H. pylori, and long-term use of acid-reducing medicines can all keep iron from being absorbed.

How iron deficiency is diagnosed

• Complete blood count (CBC). This measures hemoglobin and the size of your red blood cells.
• Ferritin. This shows how much iron is stored. A low level confirms iron deficiency. Ferritin rises with inflammation, so a normal result doesn’t always rule it out.
• Iron, TIBC and transferrin saturation. With iron deficiency, blood iron is low and the total iron-binding capacity (TIBC) is high, because the body makes more of the protein that carries iron. The share of that protein carrying iron (saturation) is low.

Then your doctor looks for the cause. This may include a celiac blood test, a test for H. pylori, questions about your periods, and in many adults a colonoscopy and an upper endoscopy to look for bleeding.

Iron deficiency treatment

Iron pills

Ferrous sulfate is the most common pill. Ferrous gluconate, ferrous fumarate and liquid forms for children are also used. Your doctor may suggest taking iron once a day or every other day, which can be easier on the stomach and still works well.

• Iron absorbs best on an empty stomach. If it upsets your stomach, take it with a small amount of food.
• Vitamin C, such as a glass of orange juice, may help absorption.
• Don’t take it with tea, coffee, milk, calcium or antacids. Space it a few hours from thyroid medicine and some antibiotics.
• Black or dark green stools are normal. Constipation and nausea are common side effects.

You’ll usually feel better within a few weeks. Most people keep taking iron for about 3 months after their blood count is normal, to refill their stores. Keep iron pills locked away from children. An overdose can be deadly. If a child swallows iron pills, call Poison Help at 1-800-222-1222.

IV iron

Iron through a vein is used when pills cause too many side effects, don’t work, can’t be absorbed, or when iron is needed quickly, such as late in pregnancy or before surgery. Newer types can be given in one or two visits. Serious allergic reactions are rare.

Treating the cause

This may mean treatment for heavy periods, removing a polyp, treating celiac disease or an ulcer, or changing a medicine. A blood transfusion is needed only for severe anemia.

Foods with iron

Iron from meat, poultry, fish and shellfish is absorbed best. Beans, lentils, tofu, spinach, pumpkin seeds and iron-fortified cereals also have iron, and eating them with vitamin C helps. Food can keep iron levels up, but once you are low, diet alone usually works too slowly, so pills are needed.

When to see a doctor

• You feel tired, short of breath or weak for weeks
• You have heavy periods or are pregnant
• You crave ice or have restless legs
• You have stools that are black and tarry, or blood in your stool

Don’t take iron for months without a blood test. Too much iron can build up and harm the liver and heart.

Get emergency care for chest pain, fainting, severe shortness of breath, vomiting blood or black, tarry stools.

Common questions about iron deficiency

Can low iron cause muscle or joint pain?

Low iron can cause muscle aches, weakness and cramps, because muscles get less oxygen. It also causes restless legs. Joint pain is not a usual sign of iron deficiency, so if your joints hurt or swell, your doctor should look for another cause, such as arthritis.

Can low iron cause anxiety or panic attacks?

Anemia can cause a racing heart, shortness of breath and dizziness, which can feel like panic. Low iron is also linked with anxiety and low mood. Treating it may help, but panic attacks have many causes, so tell your doctor about them.

Is low iron a sign of cancer?

Usually not, but it can be. Cancers of the colon or stomach can bleed slowly without other symptoms, and low iron may be the first clue. That is why men and women past menopause with unexplained low iron are usually offered tests of the gut.

How long does it take to fix iron deficiency?

Most people feel better within a few weeks of starting iron pills. Hemoglobin often returns to normal in about 2 months. Refilling the body’s stores takes longer, so treatment usually lasts 3 to 6 months. IV iron works faster. If the cause, such as heavy periods, continues, low iron can come back.

Questions to ask your doctor

• Do I have iron deficiency anemia, or low iron without anemia?
• What is causing my low iron?
• Do I need tests of my stomach or colon?
• Which iron pill should I take, and when?
• When will you recheck my blood?

Learn more

• Iron-deficiency anemia (National Heart, Lung, and Blood Institute)
• Iron deficiency anaemia (NHS)

This guide is general information and doesn’t replace advice from your own doctor. Last updated October 2026.