Although many foods contain the mineral iron, various factors affect iron absorption. If you are deficient in iron, you can develop anemia, one of the most common nutrient deficiencies in the world. Foods with certain minerals or antioxidants can inhibit your iron absorption. Tea contains polyphenols and tannins, which can affect your absorption of iron.
How much iron your body can absorb depends on your iron supply, the type of iron you consume and dietary factors. People with a lower supply of iron in reserve will absorb more than people who have sufficient levels of iron. The two types of iron are heme iron, found only in animal flesh, and nonheme iron, which is in animal and plant sources. Your body absorbs 25 to 35 percent of the heme iron you consume. The majority of iron in the diet comes from nonheme iron, but your body can only absorb approximately 3 percent of this type of iron.
Polyphenols and Tannins
Polyphenols are a type of phytochemical found in plants. According to the "American Journal of Clinical Nutrition," polyphenols are the most abundant antioxidant in the diet. Tannins, a specific type of polyphenol found in many different types of plants, bind together to help to form proteins. Tannins have a number of potential health benefits; however, these compounds can affect iron absorption. Tea contains tannins along with other polyphenols in varying levels.
Various research studies have suggested polyphenols and tannins can inhibit iron absorption. Penn State nutritional scientists examined a polyphenol found in green tea called epigallocatechin-3-gallate and how it affects iron absorption in a 2010 study published in "The Journal of Nutrition." The research team discovered these polyphenols bind to iron in the intestinal cells, forming a complex that cannot enter the bloodstream. Instead, your body passes this polyphenol complex through the feces and cannot absorb the necessary iron.
Adult women who have not gone through menopause need 18 grams of iron per day. If you are concerned about iron absorption, drink tea between meals rather than with iron-rich foods. You may also want to increase heme iron in your diet, since consuming foods with polyphenols or tannins does not influence the absorption of heme iron. Pair iron-rich plant foods with foods or beverages high in vitamin C to increase iron absorption.
- Colorado State University: Iron
- American Journal of Clinical Nutrition: Polyphenols-Antioxidants and Beyond
- Cornell University: Tannins- Fascinating but Sometimes Dangerous Molecules
- Wishard Hospital: Green Tea Extract
- Science Daily: Polyphenol Antioxidants Inhibit Iron Absorption
- Critical Reviews in Food Science and Nutrition: Effect of Tea and Other Dietary Factors on Iron Absorption
- VeganHealth.org: Iron
- VeganHealth.org: Iron
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