Iron supplements are appropriate for specific groups of people, not everyone. The people who benefit most include pregnant women, those with heavy menstrual periods, vegetarians and vegans, endurance athletes, and people with certain chronic conditions like kidney disease or restless leg syndrome. Taking iron when you don’t need it can cause harm, so understanding whether you fall into one of these categories matters.
Pregnant Women
Pregnancy dramatically increases iron demand. A pregnant woman needs roughly 1,000 mg of additional iron over the course of her pregnancy to support the growing baby, expanded blood volume, and placenta. In the first trimester, daily iron needs are relatively modest at about 0.8 mg of absorbed iron. By the second trimester, that jumps to 4 to 5 mg per day, and in the third trimester it exceeds 6 mg daily. Most women cannot meet these demands through food alone, which is why prenatal vitamins routinely contain iron.
The World Health Organization sets the hemoglobin threshold for anemia in pregnancy at 110 g/L, slightly lower than the 120 g/L cutoff for non-pregnant women. If your provider checks your ferritin level and it falls below 30, you’re considered iron deficient even if your hemoglobin still looks normal. Many women enter pregnancy with borderline iron stores, making supplementation important from early on.
People With Heavy Periods
Heavy menstrual bleeding is one of the most common causes of iron deficiency in premenopausal women. Each period involves blood loss, and blood is the body’s primary vehicle for iron. When periods are heavy, meaning you soak through a pad or tampon every hour for several consecutive hours, or your period lasts longer than seven days, the monthly iron loss can outpace what you absorb from food.
Over months and years, this steady drain depletes iron stores. You may develop iron deficiency long before you become anemic, experiencing fatigue, brain fog, and exercise intolerance while your hemoglobin still tests within the normal range. If your periods are consistently heavy, checking your ferritin level is a reasonable step. A level below 30 confirms depleted stores and supports the case for supplementation.
Vegetarians and Vegans
The iron in plant foods (non-heme iron) is absorbed at a rate of about 2 to 10%, compared to 25 to 30% for the iron found in meat, poultry, and fish. This difference is large enough that nutrition guidelines recommend vegetarians and vegans aim for significantly higher daily iron intake. The Institute of Medicine suggests 14 mg per day for men on plant-based diets (versus 8 mg for omnivores) and 32 mg per day for premenopausal women (versus 18 mg). That 32 mg target is difficult to hit through food alone, even with careful planning.
Not every vegetarian or vegan will become iron deficient, but the risk is elevated, particularly for women of childbearing age who are already losing iron through menstruation. If you follow a plant-based diet and notice persistent fatigue, weakness, or difficulty concentrating, a ferritin check can clarify whether iron is the issue. Many plant-based eaters find that a low-dose supplement provides useful insurance.
Endurance Athletes
Endurance runners and other high-volume athletes lose iron through several overlapping mechanisms. The repetitive impact of running destroys red blood cells in the feet, a process called foot-strike hemolysis. Athletes also lose iron through sweat and through small amounts of gastrointestinal bleeding that can occur during prolonged exercise. On top of this, intense training expands blood volume, diluting the concentration of red blood cells and making iron status appear even worse on lab tests.
Sports-related anemia is common enough in distance runners that routine ferritin screening is standard practice in many sports medicine clinics. Athletes whose ferritin drops below 30 to 35 often notice declines in performance, recovery, and energy well before clinical anemia develops. If you train at high volume and your performance has plateaued or declined for no clear reason, iron status is worth investigating.
People With Restless Leg Syndrome
Iron plays a role in producing dopamine, the brain chemical involved in movement control. When iron stores are low, restless leg syndrome symptoms, the uncomfortable urge to move your legs that worsens at night, can intensify. Clinical guidelines recommend iron supplementation for people with restless leg syndrome whose ferritin level is below 75, a threshold that’s notably higher than the standard cutoff for iron deficiency. In many cases, practitioners start supplementation when ferritin falls below 50.
A key finding from clinical trials: oral iron supplementation improved restless leg symptoms in patients with low ferritin, but showed no benefit in patients whose ferritin was already above 75. This suggests iron only helps when stores are genuinely low, reinforcing the importance of testing before supplementing.
People With Chronic Kidney Disease
The kidneys produce a hormone that signals the bone marrow to make red blood cells. When kidney function declines, this signal weakens, and anemia often follows. Iron deficiency compounds the problem. Current kidney disease guidelines recommend checking iron status in anyone with chronic kidney disease and anemia, using a transferrin saturation of 20% or below and a ferritin of 100 or below as markers that supplementation is clearly warranted.
Iron management in kidney disease is more complex than in otherwise healthy people, and the treatment approach depends on the stage of disease and whether dialysis is involved. But the core principle holds: iron deficiency is extremely common in this population and treating it can reduce the need for other interventions like blood transfusions.
Iron Deficiency Without Anemia
One of the most underrecognized situations is iron deficiency that hasn’t yet progressed to anemia. Your body can be running low on stored iron while your hemoglobin remains technically normal. Symptoms at this stage include fatigue, poor concentration, reduced exercise capacity, hair thinning, and feeling cold. Ferritin below 30 in a clinical setting is considered diagnostic of depleted iron stores, even if your complete blood count looks fine.
This matters because many people are told their blood work is “normal” based on hemoglobin alone. If you have symptoms consistent with iron deficiency, specifically ask for a ferritin level. It’s the most sensitive and specific marker for iron stores. In people with chronic inflammatory conditions like autoimmune disease, ferritin can be artificially elevated by inflammation, so the diagnostic threshold rises to 100.
How to Get the Most From Iron Supplements
If you do need iron, how you take it affects how much your body actually absorbs. A study published in JAMA Network Open found that taking iron every other day rather than daily resulted in a 34% higher rate of absorption. This happens because a dose of iron triggers a hormone that temporarily blocks further absorption for about 24 hours. Spacing doses out gives that signal time to reset.
Timing relative to food and drink also matters substantially. Coffee consumed with a meal reduced iron absorption by 39% in one study, and stronger coffee reduced it even further. Interestingly, coffee consumed one hour before a meal had no effect on absorption, but coffee consumed one hour after a meal inhibited absorption just as much as drinking it during the meal. Tea has an even stronger inhibitory effect. Calcium-rich foods and dairy also compete with iron for absorption.
Taking iron with a source of vitamin C enhances absorption. An empty stomach is ideal for absorption but harder on digestion. If iron upsets your stomach, taking it with a small amount of food (avoiding dairy and coffee) is a reasonable compromise. Many people find that alternate-day dosing also reduces the nausea and constipation that make iron supplements hard to tolerate.
Who Should Not Take Iron Supplements
Iron is not a general wellness supplement. Unlike vitamin D or omega-3s, taking iron when your stores are already adequate provides no benefit and introduces real risk. The body has no efficient way to excrete excess iron, so it accumulates in organs. The European Food Safety Authority was unable to establish a traditional upper intake level for iron because of this toxicity concern, instead setting a “safe level of intake” at 40 mg per day for adults, including both dietary and supplemental sources.
People with hemochromatosis, a genetic condition that causes excessive iron absorption, should avoid iron supplements entirely. The condition is more common than many people realize, affecting roughly 1 in 200 people of Northern European descent. Routine blood donation can also affect iron status in the opposite direction, making regular donors more likely to need supplementation. The bottom line: get your ferritin tested before starting iron, and recheck it periodically to make sure you’re heading in the right direction without overshooting.