Iron: The Essentials
Iron, one of the most abundant metals on earth is one of the most commonly misunderstood dietary minerals. It is essential to human metabolism and integral to many proteins and enzymes in the body. Iron’s arguably most important role is transporting oxygen around the body in the blood; thus a deficiency limits the delivery of oxygen to cells, which can result in fatigue, decreased immunity, dizziness, hair loss, decreased ability to concentrate, and more.
In the body, the majority of iron is found in hemoglobin, the protein in red blood cells that carries oxygen; as well as in myoglobin, the protein that helps supply oxygen to muscle. The body also stores iron, which is regulated by intestinal iron absorption.
There are two types of dietary iron, heme and nonheme. Heme iron is derived from animal products, such as read meat, fish and poultry, and comes directly from hemoglobin. Heme iron is easily absorbed by the body, as it is in the exact structure that the body needs and does not need to undergo any changes once ingested. Nonheme iron on the other hand is found in plant food such as legumes (i.e. lentils), spinach, prunes and more. Nonheme iron is the form of iron that is used to fortify and enrich certain foods. Nonheme iron is not as easily absorbed (less bioavailable) as heme iron and needs to be broken down in the stomach, and then carried into the blood stream from the digestive tract by transferren.
Vitamin C aids in the absorption of nonheme iron, while calcium and tannins (found in coffee and tea) reduce absorption. For this reason you may have heard not to drink coffee or tea with your breakfast, as most breakfast cereals are enriched with iron, and the tannins in these beverages will inhibit absorption of this essential mineral. Instead you may want to eat vitamin C rich foods like citrus fruits, kiwi, strawberries, green leafy vegetables (kale, broccoli, collards), bell peppers, and cauliflower with you meals. Cooking foods in cast iron pans can also increase the iron content of foods.
Since vegans and vegetarians don't eat animal products how does their iron intake compare? The American Dietetic Association reports that the, “incidence of iron deficiency anemia among vegetarians is similar to that of non-vegetarians. Although vegetarian adults have lower iron stores than non-vegetarians, their serum ferritin levels are usually within the normal range.”
Here are a handful of the best sources of iron you can find in your local supermarket:
Heme iron sources and iron content:
3.5 oz chicken liver, 12.8 mg.
3 oz canned oysters, 5.7 mg.
4 oz shrimp, 3.5 mg.
3 oz lean beef, 3.2 mg.
3.5 oz dark meat turkey, 2.3 mg.
3 oz. canned clams, 23.8 mg.
Nonheme sources of iron and iron content: breakfast cereals are often fortified, read labels as amounts vary.
1 cup boiled soybeans (edamame), 8.8 mg.
4 oz quinoa, 7.8 mg.
1 cup boiled lentils, 6.6 mg.
1 cup spinach boiled, 6.4 mg.
1 cup kidney beans, 5.2 mg.
1 cup blackeye peas, 4.3 mg.
1 tablespoon blackstrap molasses 3.5 mg.
8 oz shitake mushrooms, 3.6 mg.
1 cup black peas, 3.6 mg.
½ cup fresh spinach, 3.2 mg.
The recommended dietary allowances vary throughout life. For non pregnant women 19 -50 years old the RDA is 18mg. Men of the same age’s RDA is 8mg.
Note: consuming iron rich foods is a great way to obtain necessary iron but absorption varies person to person. The NIH points out that healthy adults absorb about 10 to 15 percent of dietary iron. Factors that influence absorption include, storage levels of iron and the type of dietary iron consumed. Heme iron absorption ranges from 15 to 35 percent. By contrast only 2 to 20 percent of nonheme iron in plant foods is absorbed. As mentioned vitamin C increases nonheme iron absorption.