Iron plays a very important role in the human body, as it is needed for many biochemical reactions. Primarily, it is necessary for the function of the respiratory chain and in erythropoiesis--red blood cell production. In order for these processes to function optimally, iron must be readily absorbed in the intestine. Various foods and beverages, including tea, can optimize or inhibit this process.
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There are two different forms of dietary iron: heme and non-heme. Heme iron is found in animal products and is more readily absorbed into the system; non-heme iron is found in plant-based foods and its absorption is influenced by other dietary factors. Thus, in order to maintain healthy iron levels, eating a balanced diet is extremely important. Blood iron levels are key to your overall health as approximately 80 percent of absorbed iron is used for hemoglobin synthesis. The absence of iron inhibits oxygen from being properly transported throughout the body.
Tea, especially black tea, reduces non-heme dietary iron absorption, primarily because of a high tannin concentration. Tannins are naturally occurring bitter plant polyphenols with an ability to bind and precipitate proteins, thus they can affect nutrition by their ability to form complexes with numerous molecules. This includes their ability to chelate--bind to--iron in the gut and prevent its intestinal absorption. Thus, it is unwise to consume tea with a meal--especially vegetarian meals in which the consumed iron is predominately non-heme iron and already less easily absorbed.
A study published in the "British Journal of Nutrition" looked at the effects of herb teas, black tea, coffee and cocoa on the absorption of non-heme iron in 77 volunteers. Researchers discovered that black tea--high in tannins--reduced iron absorption from a bread meal by 77 to 94 percent, peppermint tea by 84 percent and chamomile by 47 percent. When observing the samples at an identical concentration of total polyphenols, black tea was more inhibitory than cocoa and herb teas and equal to that of peppermint tea. The study confirms the theory that tea should not be consumed with a meal containing non-heme iron and could contribute to low blood iron in individuals consuming excess amounts of tea.
How to Improve Low Blood Iron
Studies have found that a deficiency of additional nutrients also contributes to anemia -- low iron, hemoglobin and red blood cell levels. Consequently, adequate consumption of multiple nutrients is required. Vitamin A, folic acid, vitamin B12, vitamin B6 and riboflavin deficiency can also impair erythropoiesis. Vitamin A, riboflavin and vitamin C deficiency can impair iron store mobilization, and vitamin E deficiency can cause damage to the erythrocytes--red blood cells. In regards to improving iron absorption, vitamin C intake is key. Studies have found improved hemoglobin levels in iron-deficient children after increasing their vitamin C intake, primarily in those consuming a plant-based diet, as vitamin C is a strong promoter of iron absorption and can counteract inhibitory effects of tannins and dietary phytates--a compound found in nuts, grains and seeds with a binding affinity to various minerals, preventing optimum absorption in the body.
- Cornell University: Department of Animal Science
- Proceedings of the Nutrition Society; Iron nutrition in the UK: getting the balance right; Susan J. Fairweather – Trait.
- British Journal of Nutrition; Inhibition of non - heme iron absorption in man by polyphenolic - containing beverages; Richard Hurrell et al.
- British Journal of Nutrition; Micronutrient interactions: effects on absorption and bioavailability; Brittmarie Sandström.
- Public Health Nutrition; The role of vitamins in the prevention of anaemia; Steven M Fishman et al.
Megan Grover is a working nutritionist holding a Bachelor of Science from Waynesburg University and a Master of Science in human nutrition from the University of Sheffield. She has experience in primary and secondary scientific research.