Iron fills such life-sustaining roles, from carrying oxygen throughout your body to producing energy and forming antioxidants, that getting a sufficient amount in your diet is essential. But you could eat foods high in iron and still be deficient because one type of iron, called nonheme, is not well absorbed during digestion. The good news is that eating vitamin C at the same time as nonheme iron significantly increases its absorption.
Two Types of Iron
Iron is available in two different forms: heme and nonheme. Heme iron comes from animal-based foods, including dairy products, meat, poultry and fish. Meat and dairy products may also contain some nonheme iron, but nonheme is the only type of iron you'll get from plant-based foods, according to the Linus Pauling Institute. Chicken liver, oysters, dark meat chicken and turkey, beef liver and other cuts of beef are good sources of heme iron. Some of the top sources of nonheme iron include fortified cereals, beans, spinach and lentils, notes the Office of Dietary Supplements.
All Iron is Not Equal
Eating food high in iron does not guarantee your body will get a sufficient amount because it absorbs the two types of iron differently. About 15 to 35 percent of heme iron is absorbed into your system, compared to only 2 to 20 percent of nonheme iron, according to the Office of Dietary Supplements. The amount of iron absorbed during digestion is also affected by other foods consumed at the same time as iron-containing foods. Once again, heme iron has the advantage. The absorption of heme iron is not significantly impacted by other foods, while nonheme iron is strongly influenced by foods that may enhance or inhibit its absorption.
Vitamin C Boosts Iron Absorption
Vitamin C, also called ascorbic acid, strongly enhances the absorption of nonheme iron, but it must be consumed at the same time as the nonheme iron. When they're digested together, vitamin C combines with nonheme iron to form a compound that's more easily absorbed. If the iron in your meal comes from plant-based foods, you should include at least 25 milligrams of vitamin C in the same meal, notes "Human Vitamin and Mineral Requirements." You'll get at least that much vitamin C from one serving of cauliflower, cabbage, broccoli, sweet peppers, tomatoes and Brussels sprouts, and double that amount from citrus fruits and juices.
Foods That Inhibit Absorption
Some types of foods have the opposite effect of vitamin C and inhibit nonheme absorption. While it can reduce the effect of nonheme inhibitors, vitamin C can't prevent them from interfering with nonheme iron absorption. Beans, grains and rice contain a substance called phytic acid, which binds with nonheme iron and prevents absorption. A small amount of phytic acid can lower absorption by 50 percent, according to the Linus Pauling Institute. On the flip side, vitamin C can nearly double the absorption of nonheme iron, according to Virginia Commonwealth University. Phytochemicals in some fruits, vegetables, coffee, tea and wine can also inhibit absorption of nonheme iron.
Recommendations and Warnings
The recommended dietary allowance for iron is 8 milligrams daily for adult men and postmenopausal women. Premenopausal women should get 18 milligrams of iron daily and the amount increases to 27 milligrams if you're pregnant. If you follow a vegetarian diet, you're at an increased risk for iron deficiency and should adjust your daily intake to 14 milligrams daily for adult men and postmenopausal women and 33 milligrams for premenopausal women, according to the Linus Pauling Institute. If you have any concerns about your iron intake, consult your healthcare provider before taking supplements. Iron can become toxic, so you should never consume more than 45 milligrams daily.