Iron deficiency affects a wide range of people, but certain groups face a significantly higher risk due to how their bodies use, absorb, or lose iron. Women of reproductive age, pregnant women, infants and toddlers, people with digestive disorders, endurance athletes, frequent blood donors, and anyone with chronic kidney disease or a history of weight-loss surgery are all at elevated risk. Understanding why each group is vulnerable can help you recognize the signs early.
Women With Heavy Periods
Menstruation is the single most common reason premenopausal women develop iron deficiency. Every menstrual cycle drains iron from the body, and when bleeding is heavy, losses outpace what diet alone can replace. In studies of women with heavy menstrual bleeding, 45% had ferritin levels below 30 ng/mL, the threshold most guidelines use to flag depleted iron stores. Nearly one in five had hemoglobin low enough to qualify as anemic.
What makes this tricky is that many women normalize heavy periods and never connect their fatigue, brain fog, or breathlessness to iron loss. If your periods regularly soak through a pad or tampon every hour or two, last longer than seven days, or involve large clots, your iron stores are likely taking a hit with every cycle.
Pregnant Women
Pregnancy dramatically increases the body’s demand for iron. A woman who weighs about 120 pounds needs roughly 1,000 mg of iron over the course of a full pregnancy to support the growing placenta, the expanding blood supply, and fetal development. Daily iron requirements climb from about 0.8 mg in the first trimester to 4 to 5 mg in the second trimester and over 6 mg in the third.
The body adapts by ramping up iron absorption as the pregnancy progresses, but even an excellent diet can’t keep pace with third-trimester demands. A woman needs to enter pregnancy with at least 300 mg of stored iron to have a realistic chance of meeting her needs without supplementation. Many women start pregnancy already low, especially if their periods were heavy beforehand, which compounds the problem.
Infants and Toddlers
Babies grow rapidly, and that growth requires a steady supply of iron for brain development and red blood cell production. Full-term infants are born with enough stored iron to last about four to six months, but after that, they depend entirely on dietary sources. This is the window where risk spikes.
Cow’s milk is a major culprit. It contains very little iron, and its high calcium and casein content actively blocks the absorption of non-heme iron from other foods. Even more concerning, cow’s milk consumption before age one can trigger small amounts of intestinal bleeding in about 40% of otherwise healthy infants, directly draining iron from the body. This bleeding typically stops after a child’s first birthday, but the damage to iron stores can already be done. Pediatric guidelines recommend iron-fortified formula or breast milk for the first year and delaying cow’s milk as a primary drink until at least 12 months.
People With Celiac Disease or Inflammatory Bowel Conditions
Iron is absorbed in a very specific part of the small intestine: the duodenum. That happens to be the exact location where celiac disease causes the most damage. When gluten triggers an immune response in someone with celiac disease, it flattens the tiny finger-like projections (villi) that line the duodenum and are responsible for pulling nutrients, including iron, into the bloodstream. With those villi damaged, iron simply passes through without being absorbed.
Inflammation adds a second layer of trouble. When the gut is inflamed, the body produces a hormone called hepcidin that essentially locks iron inside cells and prevents it from entering the bloodstream. This means even if you’re eating plenty of iron-rich food, your body hoards it in storage rather than using it. Stubborn iron deficiency is often the first sign of undiagnosed celiac disease, and it can persist even after switching to a gluten-free diet if the gut hasn’t fully healed.
Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis create similar problems through chronic intestinal inflammation and, in many cases, ongoing blood loss from ulcerated tissue.
People Who Have Had Bariatric Surgery
Weight-loss surgeries, particularly gastric bypass, physically reroute the digestive tract and reduce the area available for nutrient absorption. The consequences for iron status are long-lasting. In a large study following patients for a decade after surgery, about 20% of women had anemia at the five-year mark, and that rate held steady at nearly 19% at ten years. Men caught up over time, reaching a similar 19% rate by year ten.
Despite 45% of patients taking oral iron supplements a decade after surgery, many still couldn’t restore normal hemoglobin levels. The need for intravenous iron more than doubled over that period, climbing from 5% to 11%. If you’ve had bariatric surgery, iron monitoring isn’t a short-term concern. It’s a lifelong one.
Endurance Athletes
Runners, cyclists, and other endurance athletes lose iron through several overlapping mechanisms that most people never think about. The most significant is gastrointestinal bleeding: during intense exercise, blood flow to the gut can drop by more than 50%, which can damage the intestinal lining enough to cause small amounts of bleeding. Repeated training sessions create a cumulative effect.
Runners face an additional risk called foot-strike hemolysis. Each time your heel hits the ground, the impact destroys a small number of red blood cells, releasing their iron into the plasma where it’s eventually lost. Research has confirmed that heel-strike is the major cause of this type of red blood cell destruction during running. On top of that, prolonged sweating during long sessions in hot conditions contributes to gradual iron loss that adds up over weeks and months of training.
Frequent Blood Donors
A single whole blood donation of 500 mL removes approximately 240 mg of iron from the body. That’s a substantial hit. Ferritin levels drop by about 30 ng/mL over the 30 days following a donation, and recovering those stores takes far longer than most donors realize.
In a randomized trial published in JAMA, donors who took iron supplements after giving blood needed a median of 76 days to recover their iron stores. Donors who didn’t supplement fared much worse: 67% had not recovered their iron stores even after 168 days (nearly six months). If you donate blood two or three times a year without supplementing, you may be perpetually iron-depleted without knowing it.
People With Chronic Kidney Disease
Chronic kidney disease creates a perfect storm for iron deficiency. Damaged kidneys can’t clear hepcidin efficiently, so levels of this iron-regulating hormone build up in the blood. High hepcidin blocks iron absorption in the gut and traps existing iron inside storage cells, preventing it from reaching the bone marrow where red blood cells are made. The inflammation that accompanies most kidney diseases drives hepcidin even higher.
At the same time, people with kidney disease often lose iron through gastrointestinal bleeding, which is more common in this population. The result is a form of iron deficiency where standard blood tests may show adequate iron in storage, but the body can’t actually access or use it. This “functional” iron deficiency is distinct from the straightforward depletion seen in other groups and typically requires different treatment approaches.
Vegetarians, Vegans, and Restrictive Eaters
Plant-based diets contain only non-heme iron, which the body absorbs less efficiently than the heme iron found in meat, poultry, and fish. This doesn’t mean vegetarians and vegans will inevitably become deficient, but they do need to be more strategic about their food choices.
Several common foods and drinks actively interfere with non-heme iron absorption: coffee, tea (including decaffeinated), soda, dairy products, calcium supplements, foods high in dietary fiber, and even wine and beer. Pairing iron-rich plant foods like lentils, spinach, or fortified cereals with vitamin C can significantly improve absorption. But if your diet regularly includes several of these inhibitors at meals, the effective iron you’re absorbing may be much lower than what the nutrition label suggests.
How Iron Deficiency Is Identified
A serum ferritin test is the most common way to assess iron stores. Current clinical practice generally considers ferritin below 30 ng/mL a sign of absolute iron deficiency, meaning your body’s reserves are genuinely depleted. When inflammation is present, the picture gets murkier because inflammation artificially raises ferritin levels. In those cases, many guidelines use a higher cutoff of ferritin below 100 ng/mL combined with a low transferrin saturation (below 20%) to identify deficiency. A ferritin above 100 ng/mL with low transferrin saturation typically points to functional iron deficiency, where iron is present in the body but locked away and unavailable.
If you fall into any of the risk groups above, a simple blood test can catch iron deficiency long before it progresses to full anemia. Fatigue, weakness, pale skin, brittle nails, and unusual cravings for ice or dirt are classic warning signs, but many people with low iron have no obvious symptoms at all until stores are severely depleted.