In the body, iron primarily functions as an oxygen carrier within the blood and muscles. It also contributes to a healthy immune system, efficient metabolism and cognitive development. When the body becomes deficient in iron, common symptoms include fatigue, weakness, headaches and pale skin. If left untreated, iron deficiency can progress to blood pressure-regulation problems and increased risk of infection. Although sneaking more spinach into your day certainly provides a healthy dose of nutrients, it’s not the best option for upping your iron intake.
Spinach and Iron
Two forms of dietary iron exist. Heme iron is found in animal foods that once contained red blood cells, such as red meats, poultry and seafood. Nonheme iron is found in plant foods, such as lentils, beans, tofu, spinach and iron-fortified cereal. The body absorbs heme iron more easily, since its composition is similar to the iron in the human body. Spinach naturally contains nonheme iron. According to the Office of Dietary Supplements, 1/2 cup of fresh boiled spinach contains roughly 3.2 milligrams of iron, while the same serving size of canned spinach contains roughly 2.5 milligrams and the frozen variety has about 1.9 milligrams.
Bioavailability refers to the ability of iron to successfully make its way from food to your bloodstream. Since the body absorbs heme iron more easily, the iron in spinach has a lower bioavailability. As a general rule, the body is only able to absorb about 3 to 8 percent of nonheme iron. The actual percentage depends on the cooking method and the quantity of other nutrients contained in the spinach. So, while 1/2 cup of fresh boiled spinach delivers 3.2 milligrams of iron, your body might absorb less than 0.3 milligram of the nutrient.
Although spinach does contain nonheme iron, it also contains oxalic acid -- which impairs the absorption of spinach’s iron into the body, further decreasing the bioavailability. High temperatures can decrease the amount of oxalic acid, so cooking your spinach before you eat it can help increase iron absorption. The McKinley Health Center also recommends pairing spinach with a heme food or a good source of vitamin C, such as tomatoes, broccoli or oranges. These simple strategies can help encourage nonheme iron absorption. However, your body still won’t be able to absorb all of the iron in spinach -- so iron deficiency is still a potential problem if you’re not getting enough iron elsewhere.
Recommended Dietary Allowance: Kids
The Office of Dietary Supplements recommends daily iron intake levels based on gender and age. Healthy infants born at full term already have a four- to six-month supply of iron -- so the adequate intake is just 0.27 milligram per day from birth to 6 months of age. This intake can be accomplished through breast milk or iron-fortified infant formula. From 7 to 12 months, the daily intake should increase to 11 milligrams. The recommended daily intake decreases to just 7 milligrams between ages 1 and 3. From 4 to 8 years of age, an intake of 10 milligrams per day is recommended. For kids age 9 to 13, the daily recommended iron intake is just 8 milligrams.
Recommended Dietary Allowance: Adults
After age 14, males need 11 milligrams until the age of 18 and then 8 milligrams per day after age 19. For women, the daily recommended intake is slightly higher. Women age 14 to 18 need 15 milligrams per day. From age 19 to 50, the daily intake increases to 18 milligrams. However, pregnant woman should aim for 27 milligrams of iron per day, while lactating women need 9 to 10 milligrams. After age 51, the daily intake drops to just 8 milligrams.
While filling your dinner plate with 2 cups of fresh boiled spinach is certainly a healthy option, it might not do much for your iron intake. An adult female in the mid-30s age range needs 18 milligrams of iron per day. But with spinach's low bioavailability, the 2-cup serving might mean just slightly more than 1 milligram of iron absorption.
Krista Sheehan is a registered nurse and professional writer. She works in a neonatal intensive care unit (NICU) and her previous nursing experience includes geriatrics, pulmonary disorders and home health care. Her professional writing works focus mainly on the subjects of physical health, fitness, nutrition and positive lifestyle changes.