Low iron usually comes down to one of three problems: you’re losing blood, you’re not absorbing iron well, or your body needs more iron than you’re taking in. Sometimes it’s a combination. Iron deficiency is the most common nutritional deficiency worldwide, responsible for roughly 455 million cases of anemia among women of reproductive age alone. Understanding which category applies to you is the first step toward fixing it.
Blood Loss Is the Most Common Cause
Every time you lose blood, you lose the iron locked inside your red blood cells. For premenopausal women, heavy menstrual periods are the single biggest driver of iron deficiency. But blood loss doesn’t have to be visible to drain your iron stores over time.
Slow, hidden bleeding inside the digestive tract is a major culprit, especially in men and postmenopausal women. Peptic ulcers, colon polyps, hiatal hernias, and colorectal cancer can all cause small but steady blood loss you might never notice in the toilet. Regular use of over-the-counter pain relievers like ibuprofen and aspirin can irritate the stomach lining enough to cause this kind of chronic internal bleeding. If your iron keeps dropping without an obvious explanation, your doctor will likely want to rule out a gastrointestinal source.
Your Gut May Not Be Absorbing Iron Properly
You could eat plenty of iron-rich food and still end up deficient if your small intestine can’t absorb it. Iron gets absorbed primarily in the upper part of the small intestine, and anything that damages or inflames that lining can block the process.
Celiac disease is a classic example. The immune reaction to gluten flattens the tiny finger-like projections (villi) that line the intestine, and this damage directly impairs iron absorption. In many people with celiac disease, unexplained iron deficiency anemia is the first clue that something is wrong, sometimes appearing years before digestive symptoms do. Crohn’s disease and other inflammatory bowel conditions can cause similar problems, particularly when they affect the upper intestine.
Surgeries that remove or bypass part of the stomach or small intestine, including many weight-loss procedures, also reduce your body’s ability to pull iron from food. And chronic inflammation from virtually any source triggers your liver to produce more of a hormone called hepcidin. Hepcidin acts like a gatekeeper: when levels rise, it blocks iron from entering the bloodstream, both from food in your gut and from iron already stored in your body. This is why people with chronic infections, autoimmune diseases, or long-term inflammatory conditions often develop iron deficiency even when their diet looks fine on paper.
Certain Medications Interfere With Absorption
Proton pump inhibitors (PPIs), the acid-reducing drugs commonly prescribed for heartburn and reflux, are linked to iron deficiency when used long term. Your stomach needs acid to convert dietary iron into a form your intestine can absorb. By suppressing that acid, PPIs reduce the amount of iron your body can extract from food. There’s also evidence that PPIs may directly increase hepcidin production, adding a second layer of interference. If you’ve been on acid-suppressing medication for months or years and your iron is low, the medication itself could be part of the problem.
Your Diet Might Not Provide Enough
Iron from food comes in two forms. Heme iron, found in meat, poultry, and fish, is absorbed relatively efficiently. Non-heme iron, found in plants, beans, fortified grains, and eggs, is harder for your body to use. Vegetarians and vegans aren’t automatically iron deficient, but they do need to pay closer attention because they rely entirely on the less-absorbable form.
What you eat alongside iron matters just as much as the iron itself. Compounds called phytates (concentrated in whole grains, beans, and bran) and tannins (found in tea, coffee, and red wine) can significantly reduce non-heme iron absorption. In one study, iron absorption dropped progressively as the amount of phytate in a bread meal increased. The good news: vitamin C counteracts these inhibitors effectively. As little as 30 mg of vitamin C (roughly the amount in a quarter of an orange) was enough to overcome the blocking effect of phytates in the same study, and about 50 mg was needed to counteract the effect of tannins. Pairing iron-rich plant foods with citrus, bell peppers, or tomatoes is one of the simplest ways to boost absorption.
Infants who don’t get adequate iron from breast milk or formula, and children who eat a limited diet, are also at risk simply because they aren’t taking in enough.
Pregnancy and Growth Increase Iron Demand
Sometimes the issue isn’t that you’re losing iron or failing to absorb it. Your body simply needs more than usual. Pregnancy is the most dramatic example. A pregnant woman’s blood volume expands by nearly 50%, and the developing baby and placenta draw heavily on maternal iron stores. The World Health Organization recommends 30 to 60 mg of supplemental iron daily during pregnancy, roughly two to four times what a non-pregnant woman typically needs from food. Without supplementation, many pregnant women can’t keep up with the demand through diet alone.
Children going through growth spurts have higher iron needs for the same basic reason: rapid production of new tissue and blood cells consumes iron faster than a normal diet may replenish it. Adolescent girls face a double hit, with growth demands stacking on top of menstrual losses.
Endurance Athletes Lose Iron in Unusual Ways
Runners and other endurance athletes are prone to iron deficiency through a mechanism most people have never heard of: footstrike hemolysis. Each time your foot hits the ground during a run, the impact physically crushes red blood cells passing through the capillaries in the sole of your foot. Research comparing runners and cyclists found that runners showed significantly more red blood cell destruction after exercise, and the key difference between the two activities was the repeated foot impact. Over weeks and months of high-volume training, this steady low-grade destruction of red blood cells adds up. Athletes also lose small amounts of iron through sweat and, in some cases, through exercise-induced gut bleeding.
How Iron Deficiency Gets Detected
The hallmark test is serum ferritin, a blood marker that reflects your body’s iron stores. In a healthy person without inflammation, a ferritin level below 30 micrograms per liter in children or below 30 in adults generally signals deficiency. But ferritin is tricky: it rises in response to infection or inflammation, which can mask a true deficiency. When inflammation is present, the WHO recommends using a higher threshold, up to 70 micrograms per liter in adults, to account for the artificial boost. This is why your doctor may order additional inflammation markers alongside ferritin to get an accurate picture.
Symptoms develop gradually. Early iron depletion often produces no symptoms at all. As stores drop further, you might notice fatigue, pale skin, cold hands and feet, brittle nails, headaches, or unusual cravings for ice or dirt (a phenomenon called pica). By the time full-blown anemia develops, you’re likely dealing with shortness of breath during routine activities, dizziness, and a noticeably fast heartbeat. Many people dismiss the early signs as stress or poor sleep, so the condition often goes unrecognized until a routine blood test catches it.