Anemia in women is most commonly caused by iron loss through menstruation, but it’s far from the only driver. Nearly 31% of women aged 15 to 49 worldwide are anemic, according to 2023 data from the World Health Organization. The reasons span everything from monthly periods to pregnancy, dietary gaps, vitamin deficiencies, and chronic inflammatory conditions.
Monthly Blood Loss and Iron Depletion
Menstruation is the single most common reason women develop anemia. Every period means lost red blood cells, and with them, lost iron. The body needs iron to make new red blood cells, so women who menstruate need significantly more dietary iron than men or postmenopausal women. The recommended daily intake for women of reproductive age is 18 mg per day, compared to just 8 mg for women over 50 who are no longer menstruating. Teenage girls need 15 mg daily starting with their first period.
Heavy periods tip the balance further. If you regularly soak through pads or tampons every hour or two, bleed for more than seven days, or pass large clots, your iron losses may outpace what even a good diet can replace. Over months or years, this gradually empties the body’s iron reserves, eventually dropping red blood cell production low enough to cause anemia. Many women assume heavy periods are just their normal, so the iron depletion builds quietly.
Pregnancy Demands on Iron and Blood Volume
Pregnancy creates a perfect setup for anemia through two simultaneous changes. First, blood plasma volume increases by 40 to 50%, diluting the concentration of red blood cells even when the body is making more of them. Red blood cell mass rises only 15 to 25%, so the math doesn’t balance out. This dilution effect alone can push hemoglobin levels into anemic range.
Second, the growing baby, placenta, and expanded blood supply all require iron. Daily iron needs jump to 27 mg during pregnancy, 50% more than the already-elevated requirement for non-pregnant women of reproductive age. Most prenatal vitamins contain this amount, but women who enter pregnancy with low iron stores often can’t catch up with a standard supplement alone. Women who are pregnant or breastfeeding also have a greater need for folate, another nutrient essential for red blood cell production, making them vulnerable to more than one type of anemia at once.
Vitamin B12 and Folate Deficiency
Not all anemia comes from low iron. Deficiencies in vitamin B12 or folate cause a distinct type where the body produces abnormally large, poorly functioning red blood cells. This can happen from not eating enough foods that contain these vitamins, or from conditions that interfere with absorbing them.
B12 deficiency has several possible roots. Pernicious anemia, an autoimmune condition, destroys the stomach cells that produce a substance the intestines need to absorb B12. Surgeries that remove part of the stomach or intestines have a similar effect. Strict vegan or vegetarian diets can also fall short on B12, since it’s found almost exclusively in animal products. Folate deficiency is more common in women who are pregnant or breastfeeding, given their increased demands.
Certain conditions raise the risk for both deficiencies: Crohn’s disease, celiac disease, type 1 diabetes, long-term alcohol use, and older age all make it harder for the body to absorb or use these vitamins. Women who restrict what they eat or who have had gastric bypass surgery are also at higher risk.
Chronic Inflammation and Iron Trapping
Women with autoimmune diseases, chronic infections, or other long-term inflammatory conditions can develop anemia even when they technically have enough iron in their body. The problem is access. When the body detects ongoing inflammation, it produces a hormone that acts as a gatekeeper for iron. This hormone blocks iron from being absorbed in the gut and prevents immune cells from releasing recycled iron back into the bloodstream.
The result is iron that’s locked away in storage, unavailable for making new red blood cells. This is sometimes called “functional” iron deficiency, because total iron stores may look normal on certain blood tests while the bone marrow is starved of the iron it needs. Conditions like rheumatoid arthritis, lupus, inflammatory bowel disease, and chronic kidney disease are common culprits. The inflammatory signals also directly suppress red blood cell production, compounding the problem.
Dietary and Absorption Factors
Even without heavy periods or chronic disease, diet alone can cause anemia if iron intake consistently falls short. This is especially relevant for vegetarians and vegans: the body absorbs the form of iron found in plant foods much less efficiently than the form in meat, poultry, and seafood. The NIH recommends that vegetarians consume nearly twice the standard iron amount to compensate.
What you eat alongside iron-rich foods matters too. Vitamin C significantly boosts absorption of plant-based iron, so pairing iron-rich meals with citrus fruits, bell peppers, or tomatoes helps. On the other hand, coffee, tea, and foods high in certain plant compounds (common in whole grains, legumes, and nuts) can block iron absorption. Taking iron supplements on an empty stomach in the morning, away from meals, avoids these interactions. Small changes in meal timing and food pairing can meaningfully shift how much iron your body actually retains.
How Iron Deficiency Is Identified
A standard blood count can flag anemia, but identifying the cause often requires checking iron stores specifically. The most useful marker is ferritin, a protein that reflects how much iron your body has in reserve. A ferritin level below 30 ng/mL is the established threshold for iron deficiency, with a sensitivity of about 92% and specificity of about 98%. Some evidence suggests that levels below 50 ng/mL already correspond with early biochemical signs of depletion, including the body ramping up iron absorption from food as a compensatory response.
Ferritin gets trickier to interpret when inflammation is present, because inflammation artificially raises ferritin levels. A woman with rheumatoid arthritis, for example, might have a ferritin of 40 ng/mL that looks normal but actually masks true iron deficiency. In these cases, additional tests measuring how much iron is actively circulating and available become important. If transferrin saturation (a measure of iron in transit through the blood) falls below 20%, iron deficiency is likely even when ferritin appears adequate.
Why Women Are Disproportionately Affected
The gap between what women’s bodies lose and what they take in explains the global scale of this problem. From the onset of menstruation through pregnancy, breastfeeding, and the accumulated effects of decades of monthly blood loss, women face a relentless demand for iron that men simply don’t. Layer on top of that the prevalence of autoimmune conditions in women (which run two to three times higher than in men for many diseases), dietary restrictions that are more common among women, and the physiological stress of pregnancy, and the 31% global prevalence figure starts to make sense.
The daily iron recommendations tell the story clearly. A teenage girl needs nearly double the iron of a teenage boy. A pregnant woman needs more than triple what a postmenopausal woman does. These shifting targets across the lifespan mean that the risk of falling behind on iron is not a single event but a recurring vulnerability at every major biological transition.