The most common causes of anemia in women

Women develop anemia more often than men because of menstrual bleeding, pregnancy, and how their bodies absorb iron. Heavy periods are the single largest reason—losing blood every month means losing iron, and if you do not replace it through diet or supplements, your red blood cell count drops. Pregnancy drains iron reserves because your body needs more blood volume to support a growing fetus. Digestive problems, thyroid disease, and certain medications also cause anemia in women at higher rates than in men, though these affect both sexes.

The type of anemia matters because the cause determines the treatment. Iron-deficiency anemia (the most common kind in women) responds to iron supplementation or dietary changes. Other types—like anemia from vitamin B12 deficiency or chronic kidney disease—need different approaches. Knowing what is causing your anemia is the first step toward stopping it.

Key Takeaways

  • Heavy menstrual bleeding is the leading cause of anemia in women of childbearing age because iron loss outpaces iron intake.
  • Pregnancy increases your body's demand for iron and blood volume, making anemia common even in women who never had it before.
  • Digestive disorders like celiac disease and inflammatory bowel disease prevent iron absorption, causing anemia regardless of how much iron you eat.
  • Thyroid problems, certain medications, and chronic kidney disease cause anemia in women through different mechanisms, each requiring specific treatment.

Heavy menstrual bleeding and iron loss

A normal period lasts three to seven days and involves losing about 30 to 40 milliliters of blood. Heavy menstrual bleeding (called menorrhagia) means losing more than 80 milliliters per period, or bleeding that lasts longer than seven days. Each milliliter of blood contains iron, so losing significantly more blood means losing significantly more iron. Over months, this deficit adds up—your body cannot replace iron fast enough, and your hemoglobin levels fall.

Heavy periods happen for several reasons. Hormonal imbalances (particularly involving estrogen and progesterone) make the uterine lining thicker and cause longer, heavier bleeding. Fibroids and polyps in the uterus physically increase bleeding. Blood clotting disorders run in families and cause heavier bleeding in women who inherit them. Thyroid problems and polycystic ovary syndrome (PCOS) also trigger heavy periods. If your periods have always been heavy, or if they suddenly became heavier, that change itself is worth discussing with your doctor because it often points to a treatable cause.

Pregnancy and the increased demand for iron

During pregnancy, your blood volume increases by about 50 percent to carry oxygen to the fetus and placenta. That expansion requires more iron to make the extra hemoglobin. At the same time, the fetus pulls iron from your stores to build its own blood supply. A pregnant woman needs about 27 milligrams of iron per day (compared to 18 milligrams for non-pregnant women), yet many do not get that much from food alone.

Anemia during pregnancy matters because it reduces how much oxygen reaches the fetus and increases the risk of premature birth and low birth weight. It also leaves you more vulnerable to infection and complications during delivery. This is why prenatal care includes iron supplementation for most pregnant women and regular blood tests to catch anemia early. If you become pregnant and have a history of heavy periods or low iron, tell your doctor at your first visit so they can monitor you closely.

Digestive problems that block iron absorption

Your body absorbs iron in the small intestine, so any condition that damages the intestinal lining or changes how it works can cause anemia even if you eat plenty of iron-rich food. Celiac disease damages the intestinal lining when you eat gluten, preventing iron (and other nutrients) from being absorbed. Inflammatory bowel disease (Crohn's disease and ulcerative colitis) causes chronic inflammation and bleeding in the digestive tract, leading to both iron loss and poor absorption. Gastric bypass surgery removes part of the stomach where iron absorption begins, making anemia common years after the procedure.

Less common digestive causes include H. pylori infection (a bacterial infection in the stomach that interferes with iron absorption) and atrophic gastritis (inflammation of the stomach lining that reduces stomach acid, which is needed to break down iron). If you have been diagnosed with any digestive disorder, or if you have ongoing stomach pain, diarrhea, or constipation alongside anemia, your doctor may test for these conditions. Treating the underlying digestive problem often resolves the anemia.

Thyroid disease and hormonal imbalance

The thyroid gland controls your metabolism and affects how your body uses iron and produces red blood cells. Hypothyroidism (an underactive thyroid) slows your metabolism and can reduce red blood cell production. Hyperthyroidism (an overactive thyroid) can cause heavy periods, leading to iron loss. Both conditions are more common in women than in men, and both can cause or worsen anemia.

Thyroid problems often develop slowly, so you might not notice them until anemia appears. Symptoms overlap—fatigue, weakness, and shortness of breath occur in both thyroid disease and anemia, making it easy to miss the real cause. A simple blood test (TSH and free T4) can rule out thyroid disease. If your thyroid is the problem, treating it with medication often improves anemia without needing separate iron treatment.

Medications and chronic health conditions

Certain medications interfere with iron absorption or increase bleeding risk. Proton pump inhibitors (used for acid reflux) reduce stomach acid, which is necessary to break down iron. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen can cause bleeding in the stomach and intestines, especially with long-term use. Blood thinners increase bleeding risk overall. If you take any of these regularly and develop anemia, your doctor may switch you to a different medication or add iron supplementation.

Chronic kidney disease causes anemia because the kidneys produce erythropoietin, a hormone that signals your bone marrow to make red blood cells. When kidney function declines, erythropoietin production drops, and red blood cell production slows. Rheumatoid arthritis and other autoimmune diseases cause anemia of chronic disease, where inflammation itself suppresses red blood cell production. Cancer and cancer treatment can damage bone marrow or cause bleeding. These conditions require treatment of the underlying disease, sometimes combined with iron supplementation or other anemia-specific therapies.

Vitamin B12 and folate deficiency

Your bone marrow needs vitamin B12 and folate to make healthy red blood cells. Without enough of either, you develop megaloblastic anemia—your red blood cells are larger than normal and do not function properly. B12 deficiency usually comes from digestive problems (pernicious anemia, where your stomach cannot absorb B12) or from a vegan diet without supplementation. Folate deficiency happens more often in women because pregnancy depletes folate stores, and some women do not eat enough leafy greens, legumes, and fortified grains to replace it.

B12 and folate deficiency cause different symptoms than iron deficiency—numbness and tingling in your hands and feet, memory problems, and mood changes can appear alongside fatigue. A blood test can measure both vitamins. If you are deficient, treatment depends on the cause: B12 injections for pernicious anemia, oral supplements for dietary deficiency, or folate supplementation if you are pregnant or planning pregnancy.

Frequently Asked Questions

Can birth control pills cause anemia?

Hormonal birth control can reduce menstrual bleeding, which actually protects against iron-deficiency anemia. However, some women experience breakthrough bleeding or spotting on certain pills, which could increase iron loss. If you develop anemia after starting birth control, discuss it with your doctor—the pill itself is unlikely to be the cause, but a change in your bleeding pattern might be.

Does being vegetarian or vegan increase anemia risk?

Plant-based diets contain iron, but it is absorbed less efficiently than iron from meat. Women who eat no animal products need to eat more iron-rich plant foods (beans, lentils, fortified cereals, dark leafy greens) and pair them with vitamin C (citrus, tomatoes, peppers) to boost absorption. B12 deficiency is a real risk on a vegan diet without supplementation, which can cause anemia. A blood test can tell you whether your diet is meeting your iron and B12 needs.

Is anemia during perimenopause normal?

Perimenopause (the years leading up to menopause) often brings irregular, heavier periods as hormone levels fluctuate. This can cause iron-deficiency anemia. Once you reach menopause and periods stop, iron loss stops too, and anemia often improves on its own. Until then, iron supplementation or treating the underlying cause of heavy bleeding can help.

Can stress cause anemia?

Stress does not directly cause anemia, but it can worsen heavy periods by affecting hormone levels, and it can reduce appetite, leading to poor nutrition. If stress is affecting your eating or your periods have become heavier during stressful times, address both the stress and the bleeding pattern with your doctor.

How do I know if my anemia is from my period or something else?

If you have heavy periods and iron-deficiency anemia, the periods are likely the cause. Your doctor can confirm this by checking your iron stores (ferritin level) and ruling out other causes through blood tests. If your anemia does not improve with iron supplementation, or if you have other symptoms (digestive problems, weight loss, joint pain), further testing may point to a different cause.