Iron

What Is Iron?

Most of the iron in the body is in hemoglobin, the protein that lets red blood cells pick up oxygen in the lungs and release it in the tissues. Muscle holds more in myoglobin, which stores oxygen for working muscle. Much of the rest is kept in reserve as ferritin, mainly in the liver, spleen and bone marrow.

Iron is also part of enzymes that make energy in cells, and it is needed for growth, brain development and making some hormones. The body has no active way to get rid of iron, so it controls how much it takes in instead: when stores are full the gut absorbs less, and when they run low it absorbs more.

Heme and Nonheme Iron

Food carries iron in two forms. Heme iron, part of the hemoglobin and myoglobin in animal flesh, is found only in meat, poultry and seafood, and it is absorbed readily. Nonheme iron is the form in beans, grains, nuts, vegetables, fortified foods and supplements, and it makes up most of the iron people eat, even in diets with meat.

How much nonheme iron you absorb depends on the rest of the meal. Vitamin C and meat, poultry or seafood eaten at the same time raise it. Phytate in whole grains and beans, polyphenols in tea and coffee, and calcium lower it.

A Day of Food With Iron

One ordinary day from foods in the Caltide library, in usual portions, with no supplements and no fortified cereal.

The kiwi adds almost no iron, but it is there for a reason: its vitamin C, eaten with the oats, helps the body absorb their nonheme iron. A cup of tea in its place would do the opposite.

Totals are rounded per portion. The figure is the iron eaten, not the iron absorbed: the body takes up about 14 to 18% of the iron in a mixed diet, and less from a mostly plant diet.

How Iron Deficiency Develops

Iron deficiency is the most common nutritional deficiency in the world, according to the WHO. It develops slowly. First the ferritin stores drain while hemoglobin stays normal. Then red blood cell production starts to slow. Only at the last stage does iron deficiency anemia appear, with tiredness, weakness, trouble concentrating and feeling cold.

The groups most at risk are pregnant women, infants and young children, women with heavy periods, frequent blood donors, and people with conditions such as celiac disease, ulcerative colitis or heart failure. Vegetarians and vegans can meet their needs, but the US RDA for them is 1.8 times higher.

When There Is Too Much Iron

Hereditary hemochromatosis is a genetic condition in which the gut absorbs too much iron and it builds up in the liver, heart and pancreas. People who have it should not take iron supplements. That is one reason to test iron levels before taking iron, rather than guessing from tiredness alone.

Common Iron Mistakes

Thinking spinach is the iron food. Raw spinach has less iron per 100 g than cooked lentils, and it is the nonheme kind. Beans, lentils and red meat do more.

Taking iron with breakfast coffee. Coffee, tea and calcium all lower absorption. An iron tablet goes further with water or a source of vitamin C, apart from dairy and hot drinks.

Treating tiredness with iron unchecked. Tiredness has many causes. A blood test for hemoglobin and ferritin shows whether iron is the problem, and how much is needed.