The Nuts and Bolts of Dietary Iron

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Iron may not be as exciting as trans fat or omega-3 fatty acids, but it deserves a place of honor. Too little or too much iron in the body can lead to serious health problems.

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What does iron do?

Iron is a mineral that is used to make red blood cells, hemoglobin (the protein in red blood cells that carries oxygen), and myoglobin (the protein that carries oxygen in muscle). It plays a role in metabolism, collagen formation, immune system function, and the production of neurotransmitters (brain chemicals), such as serotonin and dopamine.

Despite iron’s many roles, the amount of iron in the body only adds up to roughly one teaspoon. We get iron from foods or supplements, and on average, we lose about one milligram of iron each day hrough intestinal blood loss, sweat, and urine. Premenopausal women lose more iron than others from blood lost through menstruation.

Food sources of iron

Iron from foods comes in two forms, heme and nonheme. Heme iron is found in animal foods, such as meat, poultry, fish, and eggs. Nonheme iron is found in plant foods, including dark green, leafy vegetables, nuts, seeds, legumes, iron-enriched grains, and dried fruits. Pasta, white rice, and many types of bread are enriched with iron because naturally occurring iron is often lost during food processing. And many cereals are fortified with 100% of the Recommended Dietary Allowance (RDA) for iron. (Click here for a list of dietary sources of heme and nonheme iron.)

The body absorbs anywhere from 15 percent to 35 percent of heme iron, compared to 1 percent to 7 percent of nonheme iron. However, how much iron you absorb depends on several factors. If iron stores are low, the body increases iron absorption from food. Likewise, if iron stores are high, absorption will normally decrease. Iron absorption increases during a child’s growth spurt, and also during pregnancy, due to the extra demand for this mineral. Certain substances in food, such as calcium, caffeine, tannins (found in tea), and phytates (found in plant foods) can decrease iron absorption.

On the other hand, vitamin C greatly increases iron absorption from foods with nonheme iron. Following expert recommendations to eat five to nine servings of fruits and vegetables a day can help to maximize iron absorption. Another way to increase iron in your diet is to cook foods in iron pots and pans. Small amounts of iron from the cookware can leach into foods.

How much iron do you need?

Iron requirements depend on several factors, including sex and age. For example, adult men and postmenopausal women need less iron compared to children, adolescents, and women of childbearing age. Infants need very little iron (they are born with iron stores that can last them for up to six months) while pregnant women need substantially more than non-pregnant women. This table lists the RDAs for iron based on age and sex.

Iron-deficiency anemia

Iron-deficiency anemia can occur when there is not enough hemoglobin in the blood. The World Health Organization reports that iron deficiency is the most common nutrition disorder in the world, and it’s estimated that more than 30 percent of the world’s population is affected. In the United States, approximately percent of women and 2 percent of men have iron-deficiency anemia.

Insufficient iron in the body will eventually lead to iron-deficiency anemia. The body will draw from its iron reserves from the liver, spleen, and bone marrow if iron is lacking in the diet. However, when iron stores in the bone marrow also become low, the marrow cannot make enough hemoglobin for red blood cells. The resulting red blood cells are small and carry too little oxygen for organs and tissues, causing anemia.

Symptoms. Anemia may not always be quickly diagnosed, since the signs and symptoms are similar to other health conditions. However, contact your health-care provider if you experience any of the following, because they can be signs that you are anemic:

  • Fatigue
  • Weakness
  • Lightheadedness or dizziness
  • Ringing in the ears
  • Rapid heartbeat
  • Shortness of breath
  • Headaches
  • Irritability
  • Paleness
  • Difficulty concentrating
  • Brittle nails
  • Cracked lips
  • Smooth, sore tongue

Causes. Low iron levels can result from an inadequate intake of dietary iron, poor absorption, internal bleeding due to ulcers or cancer, heavy menstrual periods, pregnancy, the demands of the growing bodies of children and adolescents, or an increased loss of iron during endurance sports.

People who are on kidney dialysis often become anemic. Damaged kidneys can’t make enough of a hormone called erythropoietin, which is needed to make red blood cells. Erythropoietin and iron are also lost during dialysis. Therefore, people on dialysis typically need supplements of iron and erythropoietin to prevent anemia.

Pregnant women who are anemic may exhibit unusual conditions called pica and pacophagia. Pica is the consumption of nonedible items such as dirt, clay, or paper. With pacophagia, a person constantly craves ice. Anemia during pregnancy raises the risk of premature delivery, a low birth-weight baby, and complications in the mother.

Diagnosing anemia. If your health-care provider suspects that you have anemia, you will likely have a physical exam and special blood tests, which include a complete blood count, iron tests (to determine the type and severity of anemia), and a ferritin level test to determine the level of iron stores in the body. Sometimes a portion of the bone marrow is also obtained to better determine the cause of anemia. If your physician suspects bleeding in the digestive tract, you’ll likely need a fecal occult blood test, a colonoscopy, an endoscopy, and/ or an upper GI series (x-rays of the upper gastrointestinal tract).

People at risk. Because older infants, toddlers, adolescents, women of childbearing age, and pregnant women have higher iron needs, they are more likely to not get enough iron, putting them at risk for a deficiency. Women who have heavy menstrual periods often need more iron, as well. Women in minority groups and women from a low-income background are more likely to not meet the RDA for iron because of inadequate iron intake.

Others at risk for anemia include endurance athletes, such as long-distance runners, who can have increased iron losses from sweat and high red blood cell turnover. Vegetarians are also at risk because they limit or avoid animal foods that are the richest sources of absorbable dietary iron. However, anemia can be easily prevented in vegetarians with an eating plan rich in fruits and vegetables high in vitamin C. And there’s evidence that vegetarians actually adapt to a lower iron intake by increasing iron absorption and decreasing iron losses. Anyone who has problems malabsorption because of celiac disease, Crohn’s disease, or ulcerative colitis, for example, or who has had a portion of his intestines removed is at high risk for developing anemia.

Iron supplements

It can be tempting to take an iron supplement to prevent anemia. However, too much iron can lead to iron overload, a condition in which an excess amount of iron is found in the blood and is stored in the heart and liver, sometimes damaging those organs. Only take an iron supplement under the guidance of your health-care provider. Taking an iron supplement on your own to self-treat what you suspect is anemia may also delay the diagnosis of a more serious problem, such as a bleeding ulcer or colon cancer.

In general, most healthy people do not need to take an iron supplement. However, women with heavy menstrual periods and pregnant women are typically prescribed iron. Also, people with the following conditions may need supplemental iron, as well:

  • Bleeding problems
  • Burns
  • Intestinal diseases
  • Stomach problems
  • Removal of stomach or intestines
  • Hemodialysis

Iron supplements are sold over the counter at drugstores and come in several forms, including capsules, tablets, and liquids. Iron is also available by injection (given by a health-care provider) or infusion, and may be given to people who have difficulty absorbing iron from food or supplements, or who have stomach problems.

Possible side effects from iron supplements include the following:

  • Upset stomach
  • Heartburn
  • Nausea
  • Vomiting
  • Constipation
  • Diarrhea
  • Dark-colored stools
  • Dark-colored urine
  • Leg cramps
  • Stained teeth (from liquid supplements)

Taking iron with food or right after eating can help lessen stomach upset, and increasing fiber and fluid intake may help prevent constipation. Dark green or black stools are normal and occur due to unabsorbed iron. (However, call your health-care provider if your stools are dark with a sticky consistency, or if you see red streaks, and if you have any abdominal cramping or pain because these can indicate serious gastrointestinal bleeding.)

Unless you have a chronic condition that impairs iron absorption, iron supplements are not meant to be taken indefinitely, so follow your health-care provider’s instructions as to how long to take your supplement. If you are anemic, you may need to take an iron supplement for up to six months until the anemia resolves.

Supplement safety

Iron supplements may interfere with the absorption and action of some medicines, and can affect other medical conditions, such as kidney disease, heart disease, asthma, intestinal disorders, and stomach ulcers. Once again, it’s important to discuss taking iron supplements with your health-care provider, especially if you have any health concerns.

Certain foods (dairy foods, eggs, spinach, whole-grain foods, tea and coffee) decrease iron absorption when taken with an iron supplement. Take your iron one hour before or two hours after eating these foods. Don’t take your iron with calcium supplements and antacids. (Remember, to increase iron absorption from food and supplements, eat a food high in vitamin C with your meal, such as an orange, tomato, strawberries, or green pepper.)

Store iron supplements away from heat and light, and discard any expired supplements. Always keep iron out of the reach of children, because an iron overdose can be fatal.

If you take a multivitamin supplement or eat a fortified cereal (such as Total), be sure to check the label for the amount of iron it contains. A multivitamin supplement that contains 18 mg of iron (or a cereal that contains 100 percent of the daily value for iron, which is also 18 mg), for example, is fine for most women under 50. However, this is too much iron for men and postmenopausal women, who should choose a supplement with no more than 8 or 9 mg of iron.

Iron overload

Iron overload, in which excess iron is in the blood and becomes stored in vital organs, such as the liver and heart, can be caused by getting too much iron from a supplement. A common genetic condition called hemochromatosis can also cause the body to absorb too much iron. Over time, iron builds up in organs, leading to problems such as cirrhosis (damage to the liver) and heart failure. Hemochromatosis may be linked with diabetes, as well.

Hemochromatosis occurs in about 1 out of 250 people of Northern European descent and is less common in other ethnic groups. It is often not diagnosed until signs of organ damage occur, which is another reason why men and postmenopausal women who are not iron-deficient should not take iron supplements unless prescribed by their health-care provider.

Iron and Type 2 diabetes

Research has linked high iron levels and the development of Type 2 diabetes. A key study out of the Harvard School of Public Health looked at data from 33,000 healthy women in the ongoing Nurses’ Health Study. After 10 years of follow-up, about 700 of these women developed Type 2 diabetes. These women also had significantly higher iron stores compared to a control group of about 700 women who did not develop diabetes, and were almost three times as likely to develop diabetes than women with low iron stores.

Another study looking at 33,000 men in the Health Professionals’ Follow-up study found that men whose iron intake came primarily from red meat were at higher risk of Type 2 diabetes compared to men who got their iron from non-red meat or plant sources.

Everyday iron

It’s easy to underestimate the importance of a substance that we need so little of, but iron is important for health. In the United States, most peoples’ diets ensure that they get the right amount of iron, but if you fall into an at-risk group or if you have any questions, a registered dietitian can help make sure your eating plan is “iron clad.”

Want to learn more about meal planning with diabetes? Read “Smart Snacking With Diabetes” and “Top Tips for Healthier Eating.”

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