Low iron levels result from one or more of three basic problems: you’re not getting enough iron from food, your body can’t absorb the iron you eat, or you’re losing iron faster than you replace it. For many people, several of these factors overlap at once. Women of reproductive age need 18 mg of iron daily, more than double the 8 mg men require, which helps explain why roughly 30% of women aged 15 to 49 worldwide have anemia, most of it driven by iron deficiency.
Not Enough Iron in Your Diet
The type of iron you eat matters as much as the amount. Iron in food comes in two forms: heme iron, found in meat, poultry, and seafood, and non-heme iron, found in plants like spinach, lentils, and fortified cereals. Your body absorbs heme iron far more efficiently. A vegetarian or vegan diet can make it harder to maintain healthy iron levels not because plant foods lack iron, but because non-heme iron is simply harder for the body to use.
This doesn’t mean plant-based eaters are destined for deficiency. Eating vitamin C alongside iron-rich foods (think bell peppers with lentils, or orange juice with oatmeal) significantly improves non-heme iron absorption. The challenge is that many people don’t pair foods this way consistently enough to keep up with their daily needs.
Foods and Drinks That Block Absorption
Even if your diet contains plenty of iron, certain foods and beverages can prevent your body from absorbing it. Coffee or tea consumed with a meal can cut iron absorption by as much as 50%. The tannins in tea and coffee bind to iron in your digestive tract and carry it out of your body unused. Calcium has a similar blocking effect on both heme and non-heme iron when consumed in the same meal, so taking a calcium supplement alongside an iron-rich dinner works against you.
Other absorption inhibitors include phytates (concentrated in whole grains, legumes, and rice), soy protein, and oxalates found in spinach. This creates a frustrating paradox: spinach is often celebrated as an iron-rich food, but its oxalate content makes that iron difficult to access. Soaking or cooking beans and grains can reduce their phytate content and improve iron availability.
Chronic Blood Loss
Iron lives primarily in your red blood cells, so any ongoing blood loss drains your iron stores. The most common source in premenopausal women is menstruation. Women with heavy periods can lose enough blood each month to outpace what their diet replaces, especially if their intake is marginal to begin with.
In both men and women, slow internal bleeding from the gastrointestinal tract is a major and sometimes hidden cause. Peptic ulcers, hiatal hernias, colon polyps, and colorectal cancer can all produce small amounts of bleeding that go unnoticed for months or years. The blood loss is gradual enough that you never see it, but steady enough to empty your iron reserves. This is one reason doctors take unexplained iron deficiency seriously in men and postmenopausal women: it can be the first sign of a GI problem that needs attention.
Regular use of aspirin or other anti-inflammatory painkillers can also irritate the stomach lining and contribute to slow, chronic bleeding.
Gut Conditions That Impair Absorption
Your body absorbs iron in a specific section of the small intestine called the duodenum. Any condition that damages this area can severely limit how much iron gets into your bloodstream, regardless of how much you eat.
Celiac disease is one of the clearest examples. The immune reaction triggered by gluten flattens the tiny finger-like projections (villi) that line the duodenum and pull nutrients into the body. With those structures blunted, iron absorption drops dramatically. Celiac disease also causes low-grade intestinal bleeding in some people, and the inflammation it triggers can activate a hormone called hepcidin that further locks iron away from circulation. Iron deficiency is so common in celiac disease that it’s often the symptom that leads to diagnosis.
Inflammatory bowel diseases like Crohn’s disease can cause similar problems, particularly when inflammation affects the upper small intestine. Gastric bypass surgery, which reroutes food past the duodenum entirely, also creates a permanent risk for iron deficiency.
Medications That Reduce Stomach Acid
Your stomach needs acid to convert dietary iron into a form your intestines can absorb. Antacids and proton pump inhibitors, the medications commonly used for heartburn and acid reflux, reduce stomach acid production and can meaningfully impair iron absorption over time. If you take these medications daily for months or years, your iron stores may gradually decline even if your diet hasn’t changed.
Inflammation and Iron Trapping
Chronic inflammation from conditions like rheumatoid arthritis, kidney disease, heart failure, or ongoing infections can cause low iron levels through a completely different mechanism. When your body detects inflammation, it produces higher levels of a hormone called hepcidin. This hormone acts like a gatekeeper: it blocks iron from leaving your intestinal cells and from being released by the immune cells that recycle iron from old red blood cells.
The result is that iron gets trapped in storage and can’t reach your bone marrow to make new red blood cells. Your blood tests may even show adequate iron in storage (normal or high ferritin) while the iron circulating in your blood is too low to use. This pattern, sometimes called functional iron deficiency, is particularly common in people with chronic diseases and doesn’t respond well to dietary changes or standard iron supplements alone.
Pregnancy and Growth Periods
Sometimes iron levels drop not because of a problem but because your body’s demand has spiked. Pregnancy is the most dramatic example. Blood volume expands by nearly 50% during pregnancy, and the developing baby and placenta require their own substantial iron supply. The recommended daily intake for pregnant women jumps to 27 mg, triple what a non-pregnant man needs. About 35% of pregnant women worldwide are anemic, reflecting how difficult it is to meet this demand through diet alone.
Infants, toddlers, and adolescents going through rapid growth spurts also have disproportionately high iron needs. Babies between 7 and 12 months need 11 mg per day, the same amount as a teenage boy, because they’re building blood volume and muscle tissue at an extraordinary rate. Teenage girls face a double demand: growth plus the onset of menstruation.
Iron Loss in Endurance Athletes
Distance runners and other endurance athletes are at elevated risk for iron deficiency through several overlapping mechanisms. The repetitive impact of running can destroy red blood cells in the feet, a process called foot-strike hemolysis. Athletes also lose small amounts of iron through sweat and, during prolonged intense exercise, through minor gastrointestinal bleeding caused by reduced blood flow to the gut. Combined with the increased red blood cell production that endurance training demands, these losses can outstrip intake quickly. Runners who notice unexplained fatigue or declining performance often find low iron is the culprit.
How Daily Needs Vary by Age and Sex
Understanding your baseline requirement helps clarify why certain groups are more vulnerable. The recommended daily iron intake, set by the NIH, shifts considerably across life stages:
- Children 1 to 3 years: 7 mg
- Children 4 to 8 years: 10 mg
- Boys 14 to 18: 11 mg
- Girls 14 to 18: 15 mg
- Men 19 and older: 8 mg
- Women 19 to 50: 18 mg
- Women 51 and older: 8 mg
The sharp drop in women’s requirements after menopause reflects the elimination of monthly blood loss. Before that point, women need to absorb more than twice as much iron as men every single day, a gap that makes dietary shortfalls, absorption problems, or even modest blood loss far more consequential.