Everything You Wanted To Know About Iron

When it comes to the micronutrients your body needs for good health, iron is one of the most critical. This trace mineral helps transport oxygen to every cell in your body. It's also necessary for hormone synthesis, and a well-functioning immune system (via National Institutes of Health). Although iron's role in the body is huge, we only need a small amount each day — just a few milligrams. Iron can be obtained from meat, certain plant and fortified foods, and supplements — but not all sources are created equal. Maintaining iron levels in the body is a delicate balance, since both too little and too much can have negative consequences for our health.

According to UCSF Health, roughly 70% of iron in the body is found in hemoglobin, the oxygen-carrying protein in red blood cells, and myoglobin, a similar substance found in muscles. Approximately 6% is "a component of certain proteins, essential for respiration and energy metabolism, and as a component of enzymes involved in the synthesis of collagen and some neurotransmitters." It's also used by the immune system. The rest is stored in the form of ferritin for use when dietary iron intake is low. Men have about a gram of ferritin (a three-year supply), while women usually have only about 300 milligrams (a six-month supply).

Iron is an essential component of hemoglobin and myoglobin

Iron's most important role is as a component of hemoglobin, a protein found at the center of red blood cells and the reason for their distinctive coloring. Hemoglobin picks up oxygen from the lungs and delivers it to every cell in the body as red blood cells travel through arteries. Cells need this oxygen to produce energy and function properly. Then, as the red blood cells travel through the veins, hemoglobin binds to carbon dioxide and helps bring this waste product to the lungs, where it's exhaled. The amount of iron in your body directly impacts how much oxygen your red blood cells are able to deliver, as explained in a report by Proceedings (Baylor University. Medical Center).

Iron is also an integral component of another important protein: myoglobin. Myoglobin is similar to hemoglobin in that it has a ring of iron molecules at its center and helps transport oxygen. But unlike hemoglobin, which travels via red blood cells throughout the body, myoglobin is found only in muscle tissue. It delivers oxygen to muscle cells, particularly when they're being strained (during exercise, for example). Myoglobin also helps break down nitric oxide, a waste product that builds up in muscle cells. Myoglobin is found in skeletal (regular) muscles, cardiac (heart) muscle, and, to a lesser degree, the smooth muscle that lines your gastrointestinal tract (via StatPearls).

Iron and the immune system

Although vitamin C gets all the attention when it comes to keeping your immune system strong, iron is just as important. Being iron deficient can weaken your immune system, but the relationship between the two is complicated.

A 2010 paper published in Basic Neurosciences, Genetics and Immunology explained that iron levels in the body are important because both our own immune cells and bacterial cells need iron for growth. The genes and proteins that control iron balance in the body can produce temporary fluctuations in iron in a way that prevents invading bacteria from using it. The authors noted that both iron deficiency and iron overload (which can occur because of certain genetic conditions or overuse of iron supplements) can disrupt this process, making the body more susceptible to bacterial infections.

In another paper, published in 2011 in Archivum Immunologiae et Therapiae Experimentalis, researchers demonstrated that chronic inflammatory conditions (such as diabetes, heart disease, arthritis, and Crohn's disease) can lead to low iron levels. This is known as anemia of chronic disease (ACD). ACD occurs because cytokines, an immune molecule involved in inflammation, increases levels of hepcidin. Hepcidin is a hormone that blocks iron transport. Unfortunately, ACD doesn't respond well to oral iron supplements.

Iron is needed for growth

As a 2014 paper published in Protein & Cell noted, every cell in the body contains proteins that need iron in order to carry out important functions like DNA synthesis and repair, energy production, and cell development and division. This means that iron is critical for proper growth and development at a cellular level. So, as important as iron is for adults, it's even more critical for those in periods of rapid growth — infancy, childhood, and adolescence.

This is why children's iron needs are proportionately (and sometimes outright) higher than those of much larger adults. Babies between 7 and 12 months, for instance, need a whopping 11 milligrams of iron daily. This is more than an adult man! Toddlers between the ages of 1 and 3 need 7 milligrams. Four- to 8-year-olds need 10 milligrams, and tweens (ages 9 to 13) need 8 milligrams. When puberty hits, boys' needs jump to 11 milligrams and girls' needs increase to 15 milligrams. Because of these relatively high iron needs, babies and children are among the groups most at risk for iron deficiency (via the National Institutes of Health).

Iron and the brain

Iron is just as important for your brain as it is for the rest of your body. As a 2013 paper published in Frontiers in Aging Neuroscience explained, "Iron affects synthesis and signaling of the neurotransmitters dopamine, noradrenalin, adrenaline and 5-hydroxytryptamine, which are involved in emotion, attention, reward, movement, and various other functions." It makes sense, then, that not getting enough iron could have a big impact on your cognitive abilities and mental health.

According to research reported on by Science Daily, your body needs iron to synthesize the neurotransmitters dopamine and serotonin. These two chemicals are closely associated with depression. As Healthline explained, "Dopamine system dysfunction is linked to certain symptoms of depression, such as low motivation. Serotonin is involved in how you process your emotions, which can affect your overall mood."

In a 2018 study published in Psychiatry and Clinical Neuroscience, researchers gave over 11,000 Japanese participants questionnaires to see if there was a link between iron-deficiency anemia (IDA) and depression. Among men, IDA was present in 7.2% of depressed individuals but only 4% of non-depressed subjects. Among women, 33.4% of depressed individuals had IDA, whereas 25.8% of non-depressed women had the condition. The link between not getting enough iron and depression may be especially strong for new mothers, since pregnancy often depletes iron stores. A literature review published in 2019 in the Journal of Psychosomatic Obstetrics and Gynecology concluded that iron deficiency and/or IDA increase women's risk for postpartum depression.

Iron requirements

Considering the important roles iron plays in the body, we need surprisingly little of it. The recommended dietary allowance (RDA) for adult men and postmenopausal women is only 8 milligrams. Adult women of childbearing age (roughly ages 19 to 50) should aim to get 18 milligrams daily. A healthy pregnancy requires a substantial increase in iron intake, so the RDA for pregnant women is set at 27 milligrams. Breastfeeding women need only 9 to 10 milligrams of iron daily, depending on age. Average iron intake (from both food and supplements) among Americans ranges from 19.3 to 20.5 milligrams a day for adult men and 17 to 18.9 milligrams a day for adult women. Average intake for pregnant women, however, is only 14.7 milligrams daily — well below the RDA (via the National Institutes of Health).

According to Oregon State University, 7.8% of adults fail to meet the estimated average requirement (EAR) for iron. The EAR is a guideline of how much of a particular micronutrient someone needs in order to avoid negative health consequences. Think of the RDA as the ideal and the EAR as "good enough." The EAR for iron is 6 milligrams for adult men, 8.1 milligrams for adult women of childbearing age, 5 milligrams for postmenopausal women, 22 milligrams for pregnant women, and 6.5 milligrams for breastfeeding mothers (via the USDA).

Heme and non-heme iron

The iron we eat comes in two distinct forms: heme and non-heme. Heme iron is found only in meat. Organ meats, red meat (beef and lamb) and certain shellfish are the most iron-rich. A 2.5-ounce serving of pork liver, for example, has 13.4 milligrams of iron, while the same serving size of oysters contains 6.3 milligrams and 2.5 ounces of steak has 2.4 milligrams. White meat, fish, and certain shellfish contain less iron. For instance, 2.5 ounces of pork or chicken both contain 0.9 milligrams of heme iron, while the same serving size of shrimp, salmon, or turkey each contain 0.5 milligrams. Nonheme iron is found in plant foods and enriched products, particularly fortified cereals, beans and legumes, dark leafy vegetables, and tofu (via HealthLinkBC).

While your body can make use of both heme and non-heme iron, heme iron is much more bioavailable, meaning it's easier for your system to metabolize it and less is lost during the process. According to a paper published in The Journal of Nutrition, there are a number of factors that give heme iron an advantage. Heme iron has a different "absorption pathway" than non-heme iron and can be taken up directly by cells in the intestines. It's also not as influenced by the other micronutrients we consume. The high pH of the upper small intestine doesn't affect heme iron but can make it more difficult to break down non-heme iron.

Getting the most from the iron you eat

Your body has a difficult time absorbing the non-heme iron you consume. According to a 2010 paper published in the American Journal of Clinical Nutrition iron bioavailability tops out at about 14 to 18% for those eating an omnivore diet (that is, both heme and non-heme iron) and 5 to 12% for vegetarian diets. Actual absorption percentages may be even lower, depending on factors such as stored iron levels and the presence of other micronutrients.

What you eat alongside non-heme iron can have a big impact on how much you absorb. Vitamin C is the best-known iron helper. Consuming 100 milligrams of vitamin C (either in food or supplement form) at the same time you consume non-heme iron can boost absorption by as much as 67%. Vitamin A and carotenoids (which your body makes into vitamin A) can improve the bioavailability of non-heme iron by 80% to 200%. Interestingly, eating heme iron at the same time you eat non-heme iron (for example, adding steak to a spinach salad) increases total iron absorption by 200 to 300% (via Healthline). 

Unfortunately, there are also substances that decrease the absorption of non-heme iron, and many of them are found in iron-rich plant foods. Phytates, for instance, are "anti-nutrients" found in many whole grains, cereals, legumes, and soy and can dramatically reduce non-heme iron absorption. Coffee, tea, wine, and other polyphenol-rich beverages and foods also hinder the absorption of non-heme iron. Just 165 milligrams of calcium from milk, cheese, or a supplement can lower non-heme iron absorption by as much as 60% (via Healthline).

Iron supplements

If a doctor has advised you to get your iron levels up and food sources just aren't cutting it, iron supplements are another option. Although these are available over-the-counter without a prescription, it's generally recommended that they be taken only by those who have diagnosed iron deficiency. According to the National Institutes of Health (NIH), between 14 and 18% of Americans regularly take a supplement containing iron, although usage varies significantly among different groups. For instance, approximately 72% of pregnant women (the group with the highest need for iron) take a supplement.

Iron is sometimes included in multivitamins, particularly those aimed at women. It's also available as a standalone supplement in either tablet, gummy, or liquid form. Iron supplements can be confusing because there are many different forms of iron used, including ferrous fumarate, ferrous gluconate, ferrous sulfate, and polysaccharide iron complex. Each has a different percentage of elemental iron, which is what the recommended dietary allowance (RDA) for iron is based on. As the NIH noted, "Ferrous fumarate is 33% elemental iron by weight, whereas ferrous sulfate is 20% and ferrous gluconate is 12% elemental iron."

This means that when you pick up a package of iron supplements, the weight of the tablets isn't equivalent to how much actual iron you'll get. For instance, a 325-milligram tablet of ferrous fumarate contains 106 milligrams of elemental iron, while a 325-milligram tablet of ferrous sulfate contains 75 milligram of elemental iron and 325 milligrams of ferrous gluconate contains just 36 milligrams. Polysaccharide iron complex pills usually contain 50 milligrams of elemental iron (via the Society for the Advancement of Patient Blood Management). The strength of liquid iron supplements can also vary significantly. 

Side effects

Although supplements can be a convenient way to get the iron we need, they may come with unpleasant side effects or unintended interactions. Iron supplements are known to cause GI upset, including stomach pain, constipation or diarrhea, nausea, and vomiting (via WebMD). These side effects are more common when iron is taken on an empty stomach, but taking iron supplements with food may reduce your body's ability to absorb them.

Some types of iron supplements, especially those containing a polysaccharide iron complex, claim to be easier on the tummy, although individuals' experiences can vary greatly. Some iron supplements have an enteric coating that allows for a more controlled, extended release. This can reduce side effects but, unfortunately, may also reduce absorption. Liquid iron supplements carry the same potential side effects as tablets and may also stain teeth.

Iron supplements can also decrease the effectiveness of certain prescription medications if they're taken at or near the same time. This is particularly true for antibiotics such as tetracyclines and quinolones. Individuals taking both iron supplements and antibiotics should take iron either at least two hours before or four hours after an antibiotic dose. Iron supplements also decrease the absorption of levothyroxine (synthetic thyroid hormone), levodopa (used to manage Parkinson's disease), methyldopa (prescribed for high blood pressure), and bisphosphonates (used to prevent bone loss (via WebMD).

Iron deficiency and anemia

Not getting the iron your body needs can lead to deficiency. According to WebMD, 20% of non-pregnant women, 50% of pregnant women, and 3% of men in the United States don't have enough iron in their bodies. The Mayo Clinic outlined four potential causes of iron deficiency. Some individuals, particularly vegetarians and vegans, may not get enough iron in their diet. Others may have difficulty absorbing iron because of gastrointestinal surgery or a condition such as celiac disease that has damaged the lining of the intestines. A temporary increase in iron needs, such as during pregnancy, can also lead to deficiency because supply doesn't keep up with demand. Blood loss, such as from a heavy period, ulcer, or physical trauma, can also rapidly deplete iron stores.

According to the National Institutes of Health (NIH), "iron deficiency progresses from depletion of iron stores (mild iron deficiency), to iron-deficiency erythropoiesis ... and finally to iron deficiency anemia (IDA)." In iron-deficiency erythropoiesis (also known as marginal iron deficiency), iron stores are depleted but hemoglobin levels haven't yet been affected. In IDA, hemoglobin levels and the number and size of red blood cells are below normal.

Those most at risk for iron deficiency include pregnant women, babies and young children, women with heavy periods, frequent blood donors, people with cancer or heart failure, and those who've had gastrointestinal surgery. It's important to note that there are many other forms of anemia, although iron deficiency is the most common cause (via Mayo Clinic).

Symptoms and complications

If you aren't getting enough iron, initially you won't have any symptoms, since your body can draw on its ferritin stores for a while. In addition, there's a range for both red blood cells and hemoglobin, so everyone's "normal" is slightly different and people can begin experiencing symptoms at different levels (via Merck Manual).

If you have iron-deficiency anemia (IDA), this means your tissues and organs aren't getting enough oxygen. This leads to a set of common symptoms that can include extreme fatigue, weakness, shortness of breath, dizziness, chest pain, irregular heartbeat, headaches, tongue inflammation, pale skin, and cold hands and feet. Cosmetic issues, such as brittle or misshapen fingernails and hair loss may occur. People may also develop pica, a condition in which they start craving and consuming non-nutritive substances such as ice, dirt, or chalk. This may be the body's misguided way of trying to get the iron it so desperately needs (via Mayo Clinic).

It's probably no surprise that a condition that affects your body's ability to circulate oxygen to every cell in your body can have dire consequences if not treated. In particular, IDA can negatively affect the heart. As the Mayo Clinic explained, "When you're anemic your heart must pump more blood to make up for the lack of oxygen in the blood." Over time, untreated anemia can lead to an enlarged heart or heart failure. It can also make you more susceptible to infections.

Iron poisoning

While it's very unlikely that eating a high-iron diet will cause any adverse issues, overdoing it on iron supplements can be dangerous. As the National Institutes of Health (NIH) noted, "In severe cases (e.g., one-time ingestions of 60 mg/kg), overdoses of iron can lead to multisystem organ failure, coma, convulsions, and even death."

This is most often a problem with young children who find a bottle of iron supplements or multivitamins and swallow a large number of them. In fact, between 1983 and 1991, a third of all poisoning deaths among children were caused by iron supplements. Thankfully, that number has since declined because manufacturers are now required to package high-dose iron supplements in much harder-to-access, child-resistant packages.

Iron levels in the body can also rise to dangerous levels gradually over time — a condition known as iron overload. Normally, the body's iron regulatory system prevents this from happening, but individuals with a condition known as hereditary hemochromatosis are genetically predisposed to absorb excess amounts of iron from the digestive tract. There's no easy way for the body to get rid of excess iron in the blood except blood loss, so it builds up over time (via Healthline). If untreated, iron overload can lead to irregular heartbeat or heart failure, liver failure, diabetes, arthritis, infertility, and even death. Hemochromatosis is relatively common, affecting about 1 million Americans. Women of childbearing age are less likely to experience symptoms, however, since they regularly lose blood during their period (via Cleveland Clinic).

Cancer risks

In addition to the immediate risks posed by iron poisoning and the long-term consequences of iron overload, some experts worry that consuming too much heme (animal-based) iron may increase cancer risk. As the authors of a 2014 meta-analysis published in Cancer Epidemiology, Biomarkers & Prevention explained, iron, despite its many important functions, can act as a prooxidant under certain circumstances. This means that it can cause oxidative stress and DNA damage that, over time, could increases the risk for cancer.

It's well-documented that those with hereditary hemochromatosis are at increased risk for liver cancer, so does iron increase cancer risk for everyone? After analyzing the results of 59 previously published studies, the authors concluded that "a higher intake of heme iron has shown a tendency toward a positive association with cancer risk."

The meta-analysis found that by increasing heme iron intake by just 1 milligram per day, colon, lung, and breast cancer risks decreased. Results for other types of cancer, such as esophageal and ovarian, were mixed. Interestingly, higher ferritin levels (i.e., more stored iron) were generally linked to a decreased risk of cancer. So while heme iron circulating in the blood may cause problems, the stored form of iron appears to offer a layer of protection against cancer.

Testing iron levels

If your doctor suspects your iron levels are either too low or too high, there are a number of blood tests that can be performed. Checking levels of ferritin, an indicator of the body's stored iron, is usually the first step. Different laboratories may give slightly different ranges, but generally "normal" is anywhere between 24 and 336 mcg/L for men and between 11 and 307 mcg/L for women (via Mayo Clinic).

Depending on the results of the ferritin test or your particular symptoms, a number of other iron tests may be ordered. A serum iron test measures the amount of "active" iron circulating in the blood. Total iron-binding capacity (TIBC) is a test to gauge how much iron can attach to transferrin, the protein that helps store iron. Transferrin saturation measures what percentage of transferrin molecules have iron attached to them.

Taken together, these various tests give doctors a better picture of what's going on in your body. For example, iron deficiency is marked by low ferritin, serum iron, and transferrin saturation, but high TIBC. Hemochromatosis (iron overload) produces opposite results: high ferritin, serum iron, and transferrin saturation with low TIBC. Acute iron poisoning results in normal ferritin and TIBC, but elevated serum iron and high transferrin saturation. Those experiencing chronic illness often have low or normal ferritin, TIBC, and transferrin saturation and low serum iron (via LabTestsOnline). Using these results, doctors can get you on the path to more balanced iron levels and better health.