Tannins and polyphenols, compounds found in green tea and black tea, can hinder the absorption of nonheme iron from foods and supplements. Inadequate absorption of iron can cause iron deficiency, a condition characterized by a lack of healthy red blood cells. Tea consumption may only cause a problem for individuals with a high risk of iron deficiency.
In 2004, a review of studies published in the "Journal of Human Nutrition and Dietetics" concluded that clear evidence shows that tea inhibits nonheme iron absorption. Low iron absorption may pose a serious issue for people with a low intake of heme iron sources, a low intake of foods that enhance iron absorption or a high intake of foods that inhibit iron absorption, noted Dutch researchers in a 2000 study in the "Critical Reviews in Food Science and Nutrition."
Individuals at high risk for iron deficiency include pregnant women, low birthweight infants, teenage girls, women of childbearing age, people with kidney failure, people undergoing routine dialysis treatments and people with gastrointestinal disorders such as celiac disease and Crohn's disease. Vegetarians and vegans who consume little or no animal products may also have a higher risk of iron deficiency.
Individuals at high risk for developing iron deficiency should pay close attention to avoiding tea and other absorption-inhibiting foods at mealtime. In a 2004 study published in the "Journal of Human Nutrition and Dietetics," researchers from King's College London recommended that groups at risk of iron deficiency drink tea between meals and at least one hour after eating nonheme iron sources.
Other Factors Affecting Iron Absorption
Other food components that hinder iron absorption include calcium, proteins in soybeans, polyphenols and phytates in legumes and whole grains, according to the National Institutes of Health Office of Dietary Supplements. Vitamin C and meat proteins can boost nonheme iron absorption.
Iron Deficiency Symptoms
Common signs of iron deficiency include weakness, fatigue, difficulty maintaining body temperature, inflamed or sore tongue, difficulty concentrating and irritability. Iron deficiency may cause decreased immune function and decreased performance at work and school, notes the National Institutes of Health Office of Dietary Supplements.