Do Tea Tannins Interfere With Iron Absorption?
The tannins (polyphenols) found in Black tea and Green tea do interfere with iron absorption from meals, with a larger impact in iron absorption from plant based foods. Drinking tea at the same time as a meal presents more of an issue than tea consumption an hour or more before meals, which has much less of an impact. This effect is due to the polyphenols in true teas made from Camellia sinensis leaves, including black tea, green tea, and white tea. The type of tea, the contents of the meal, and other factors all affect how much the iron absorption is impaired. Many herbal teas (tisanes) do not produce this effect.
What are commonly called tea tannins are actually polyphenolic compounds such as catechins, theaflavins, thearubigins, and theasinensins. These polyphenols have a wide range health benefits, and are largely responsible for the rich antioxidant nature of tea. As such, they should not be viewed as negative compounds despite their ability to inhibit iron absorption. Like many aspects of nutrition, it is a matter of balance and timing.
The extent to which tea tannins interfere with iron absorption is modulated by many factors such as the amount of tea consumed, the time it was consumed, and even the type and strength of the tea! Some people absorb iron much more readily than others, so individual differences also play a part.
If you like dealing with percentages however, we can look to research on the matter to try and paint a clearer picture. A 1983 study found a 64% decrease in iron absorption when black tea was consumed with a meal (which was a hamburger, in case you were wondering). Much of the data in this study however, was focused on Coffee, which was also found to disrupt iron absorption when consumed with the meal. 
Why The Meal Matters
The meal itself also plays a role in this effect. Meals containing foods that are rich in or potentiate iron absorption such as meat, fish, poultry, and foods high in Vitamin C, all show the ability counteract the effect that tea has on iron absorption to some extent. It is not only tea that impairs the mechanism of absorption, and many other foods including soya beans, milk, eggs, and coffee all show similar effects to tea in this regard. The amount of iron absorbed from meals is also influenced by the levels of the persons iron stores, and the absorption rate is higher in individuals who have lower iron stores. 
When we consider why this effect occurs, it is important to note that dietary Iron comes in two distinct forms; Haem Iron (pronounced ‘Heem’) and Non-Haem Iron. Haem is a haemoglobin precursor that is capable of hosting an iron molecule. We go in to more detail about this subject here.
As plants and vegetables do not have blood, and therefore have no haemoglobin, Non-haem iron is the only form of iron found in plants and vegetables. This includes the vegan iron sources such as spinach, cereals, flour, and lentils. Non-haem iron is poorly absorbed even in ordinary circumstances, with an estimated absorption range of around 2% to 20%. 
Haem iron is the form found in blood and animal tissues. It is derived primarily from haemoglobin and myoglobin in animal protein sources. As it is already in a form natural to living organisms, haem iron is absorbed by the body very readily. More specifically, haem iron is absorbed intact within a porphyrin ring, which makes it very bioavailable. This high bioavailability ensures that haem iron absorption is less affected by dietary inhibitory factors such as the polyphenols in tea. 
Red meat, fish and poultry, and the offal products liver and kidney are all rich in haem iron. Around half of the iron in these foods is in the form of haem iron, and the other half as non-haem iron. Importantly, these foods also show the ability to enhance non-haem iron bioavailability by as much as four times! This means that meals containing these foods not only offer large amounts of bioavailable iron, but actually help to increase and potentiate iron absorption from the meal too. 
This difference in iron forms is important, as the two are not absorbed at the same rate. The difference also influences the extent to which tea impairs iron absorption. Research has shown that Green Tea consumption particularly impairs non-haem iron absorption. Generally, tea tannins show a more pronounced reduction in iron absorption from plant based sources. 
People following a vegetarian or vegan diet will not get the bioavailable haem iron that meat, fish, and poultry provide, as these food sources also improve iron absorption, tea consumption with meals could potentially reduce iron absorption further in these individuals. The good news, is that Vitamin C has also shown the ability to improve non-haem iron absorption, so enjoying some of the many vitamin C rich foods that the plant world has to offer may also help combat iron absorption reduction from tea. 
Those on a plant based diet may also be reassured by the fact that the general population in the UK obtain around 75% of their dietary iron from cereals, bread, fruit and vegetables, with only roughly 25% coming from haem iron sources. This is due to the fact that foods contain much more non-haem iron, so they make a larger contribution to iron intake despite their lower absorption rate. Furthermore, cereals and bread often are fortified in the production process with additional iron, in effort to increase the nutritional value of the subsequent food products.  
Fortified Wheat Flour And Tea
In Morocco, it is common for meals to be served with traditional Moroccan style green tea, and in recent years, Morocco has begun fortifying wheat flour with the addition of a non-haem iron source called Ferric Sodium EDTA. At the present time, Ferric Sodium EDTA is the World Health Organization’s preferred iron fortificant for wheat and maize flour due to it’s less metallic taste and purported better bioavailability than electrolytic iron.  This practice of fortifying wheat flour is not unique to Morocco, and is conducted in many countries around the world, with the aim of improving the iron status of populations with otherwise poor access to iron rich foods. 
In a country where tea is regularly consumed with meals however, would this move have the desired effect? In September 2021, a study was published in the Journal Of Nutrition that aimed to shed some light on the issue. In the study, two groups of Moroccan women were given a meal made with fortified wheat flour, with some participants also having green tea with the meal.
Green tea was shown to decrease absorption of the fortified iron by more than 85% in comparison to participants drinking water with their meals. The effect was observed in both non-anaemic women and anaemic women. The study reveals that attempts to boost iron levels by fortifying maize and wheat flours is likely to have a reduced impact in populations where tea is regularly consumed with meals. 
There is very conclusive data over many years that shows that tea does impact iron absorption when consumed alongside meals, and this effect seems to be increased against sources non-haem iron. To get a better picture of what this means, it is important to take a look at longer term studies to see if this produces harmful effects over longer periods, to see if this reduction in iron absorption is capable of inducing more serious clinical deficiencies.
Does Tea Lower Iron Levels?
For most people with adequate iron stores, tea consumption does not seem to significantly influence iron status. Lowered iron counts are only produced by tea consumption in individuals that already present low iron levels, or are suffering from a pre-existing iron absorption difficulties. For the vast majority of otherwise healthy individuals with average tea and food consumption habits, the reduction in iron absorption from drinking tea is unlikely to lead to clinical issues. 
This good news was supported by a study by Dr. Michael Nelson of Kings College London, looking at the effects of tea and iron status in the United Kingdom.
“There is no need to advise any restriction on tea drinking in healthy people with no risk of iron deficiency.”Dr. Michael Nelson – King’s College London 
Furthermore, regular tea drinkers may even find that the impact that tea tannins have on iron absorption to be not as pronounced as it is for individuals who only consume tea occasionally. One study found that rats given regular tea started to adapt to the tannins within by producing more proline-rich proteins in their saliva. Salivary proline-rich proteins may form complexes with tannins which serve to lessen their effect on iron absorption. It is unknown if the rats involved preferred their tea with milk or sugar. 
It is worth considering that tea is the second most popular drink in the world, with only water ahead at the number one spot. Forecasted data from the International Tea Committee suggests that around 297 billion litres of tea was consumed worldwide in 2021.  Despite this huge volume of tea consumption, there is no evidence to suggest that drinking tea produces iron deficiencies in individuals with good iron stores and healthy diets. Any risk of tea consumption presenting iron related issues seems to be isolated to those with already low iron stores, existing iron absorption issues, and populations with poor access to iron rich food sources.
Drinking tea with a meal does show a reduction in the absorption of iron. This effect however, does not seem to directly cause iron deficiencies in otherwise healthy populations. The reduction in iron absorption caused by tea may be of more reasonable concern to individuals suffering from iron deficiency anaemia, or with already depleted iron stores. For these individuals and others with already low iron counts, the decrease in iron absorption caused by black and green tea may require some consideration.
Furthermore, it is worth remembering that a meal rich foods that potentiate iron absorption will likely counteract the reduction created by tea. Meat, fish and poultry are all able to potentiate iron absorption to varying degrees. Individuals following a vegetarian or vegan diet will not get the potent haem iron that meat, fish, and poultry provide, nor their ability to counteract the iron absorption reduction effect from tea tannins. Individuals with such diets may also benefit from reducing tea consumption at meal times.
For those at risk of iron deficiencies, or those seeking to boost their iron stores, it may be sensible to limit tea consumption to between meals, rather than with meals. Research has shown that the effect is much less significant if tea is consumed at least one hour before meals. Similarly, it is advisable to wait at least one hour after eating a meal before consuming any tea. 
Under such circumstances, tea does not present a tangible risk to development of iron deficiencies.
If you want to know more about what tea tannins actually are (and why they should really be called polyphenols) you can read our article on the matter by clicking here.
1. T A Morck, S R Lynch, J D Cook, Inhibition of food iron absorption by coffee, The American Journal of Clinical Nutrition, Volume 37, Issue 3, March 1983, Pages 416–420, https://doi.org/10.1093/ajcn/37.3.416
2. Itske M. Zijp, Onno Korver & Lilian B. M. Tijburg (2000) Effect of Tea and Other Dietary Factors on Iron Absorption, Critical Reviews in Food Science and Nutrition, 40:5, 371-398, DOI: 10.1080/10408690091189194
3. Milman NT. A Review of Nutrients and Compounds, Which Promote or Inhibit Intestinal Iron Absorption: Making a Platform for Dietary Measures That Can Reduce Iron Uptake in Patients with Genetic Haemochromatosis. J Nutr Metab. 2020 Sep 14;2020:7373498. doi: 10.1155/2020/7373498. PMID: 33005455; PMCID: PMC7509542.
4. Uzel C, Conrad ME. Absorption of heme iron. Semin Hematol. 1998 Jan;35(1):27-34. PMID: 9460807.
6. Samman S, Sandström B, Toft MB, Bukhave K, Jensen M, Sørensen SS, Hansen M. Green tea or rosemary extract added to foods reduces nonheme-iron absorption. Am J Clin Nutr. 2001 Mar;73(3):607-12. doi: 10.1093/ajcn/73.3.607. PMID: 11237939.
9. Kruger J. Replacing electrolytic iron in a fortification-mix with NaFeEDTA increases both iron and zinc availabilities in traditional African maize porridges. Food Chem. 2016 Aug 15;205:9-13. doi: 10.1016/j.foodchem.2016.02.161. Epub 2016 Mar 3. PMID: 27006207.
10. Field MS, Mithra P, Peña-Rosas JP. Wheat flour fortification with iron and other micronutrients for reducing anaemia and improving iron status in populations. Cochrane Database of Systematic Reviews 2021, Issue 1. Art. No.: CD011302. DOI: 10.1002/14651858.CD011302.pub3. Accessed 13 August 2022.
11. Lazrak M, El Kari K, Stoffel NU, Elammari L, Al-Jawaldeh A, Loechl CU, Yahyane A, Barkat A, Zimmermann MB, Aguenaou H. Tea Consumption Reduces Iron Bioavailability from NaFeEDTA in Nonanemic Women and Women with Iron Deficiency Anemia: Stable Iron Isotope Studies in Morocco, The Journal of Nutrition, Volume 151, Issue 9, September 2021, Pages 2714–2720, https://doi.org/10.1093/jn/nxab159
12. Temme EH, Van Hoydonck PG. Tea consumption and iron status. Eur J Clin Nutr 56, 379–386 (2002). https://doi.org/10.1038/sj.ejcn.1601309
13. Nelson, M. and Poulter, J. (2004), Impact of tea drinking on iron status in the UK: a review. Journal of Human Nutrition and Dietetics, 17: 43-54. https://doi.org/10.1046/j.1365-277X.2003.00497.x
14. Hee-Seon Kim, Dennis D. Miller, Proline-Rich Proteins Moderate the Inhibitory Effect of Tea on Iron Absorption in Rats, The Journal of Nutrition, Volume 135, Issue 3, March 2005, Pages 532–537 https://doi.org/10.1093/jn/135.3.532
16. Ahmad Fuzi SF, Koller D, Bruggraber S, Pereira DI, Dainty JR, Mushtaq S. A 1-h time interval between a meal containing iron and consumption of tea attenuates the inhibitory effects on iron absorption: a controlled trial in a cohort of healthy UK women using a stable iron isotope. Am J Clin Nutr. 2017 Dec;106(6):1413-1421. doi: 10.3945/ajcn.117.161364. Epub 2017 Oct 18. PMID: 29046302.