Tea is known for its health benefits. However, it has a label that has stuck to it for decades: it makes you anemic, lacking in iron! Does tea put us down rather than help us? What exactly do we know about tea and iron?
Why do we need it so much for the body?
Before 1932, we didn't know how important iron was to the body! And yet, it circulates in your blood all day long. Iron is a major component of our hemoglobin, the protein in red blood cells. Iron binds oxygen molecules, which allows the red blood cells to carry it to our organs. In addition, iron is an essential element for the activity of certain molecules in the body including molecules that allow for the repair and synthesis of our DNA (Puig et al. 2017 and Abbaspour et al. 2014). Our iron is stored in our body in the liver, spleen, muscles, bone marrow and bones. (Nicolas and Vaulont, 2005) The balance of iron is going to rely on our diet and proteins providing its storage and absorption through the intestines. If there is not enough iron in the body, there is anemia.
Anemia, a more common condition than we think
It is estimated that anemia affects more than 30% of the population. To evaluate anemia, a blood test is performed to detect the amount of hemoglobin in the blood, which is correlated to the amount of iron in the blood. It is estimated that between 11 g/dL of blood and 18 g/dL of blood is required (variations exist between age and gender). Anemia can be caused by many conditions, but the most common cause is iron deficiency in the diet and during menstruation. One of the most obvious signs of anemia is severe fatigue, potentially related to a lack of oxygen transport by the red blood cells. Depending on the severity of the anemia, there may be vascular disorders, for example. A disease not to be taken lightly (Turner et al. 2020)
Tea, an iron magnet?
Among the studies on tea and iron absorption, the one by Disler et al. from 1975 is one of the best known. Briefly, the authors subjected volunteers to an iron-rich diet. They then drank either water (negative control) or tea. The authors found that the amount of iron absorbed was almost quadrupled when the people drank tea, without suffering from anemia.
This property of tea to absorb iron is linked to molecules with a thousand and one virtues: polyphenols. The polyphenols contained in tea, such as catechins, are capable of forming complexes with iron. This prevents the iron from being absorbed by the intestines. This leads to a decrease in iron levels in the body.
Are there differences in absorption between different sources of iron?
Iron is contained in many high-protein foods such as animal meat, egg whites and certain legumes (lentils, spinach, etc.). There are two forms of iron: heme (i.e. iron contained in a ring of organic molecules) and non-heme (iron in free form). The heme form is more easily absorbed by our body than the non-heme form, it is recommended to diversify its iron sources (West and Oats, 2008) (Harvard Nutrition Source). Although studies on the differences in absorption between the two irons are not, to my knowledge, available, it could be important to take this into account in the case of diets without animal products or in the context of dietary supplements (iron is in the non-hememic form, Lazrak et al. 2021)
Does tea make you anemic with high tea consumption?
The answer is not as mixed as one might think. Much has been read in recent years that tea can lead to anemia. But under what conditions? In a 1995 clinical case (Gabrielli and De Sandre 1995), a young woman presented with a chronic anemia that worsened from week to week. After investigation of her lifestyle and diet, it was found that the young woman drank more than 1.5 liters of tea per day and did not drink any other source of liquid. While the authors did not look at the amount of leaves used or the times of drinking, it can be assumed that she drank it during meals, which is the time when iron is most exposed and therefore most easily absorbed by the tea.
But what about the case where tea is consumed without excess (i.e. no more than 3 cups of tea per day)?
Studies of iron absorption from tea have been conducted primarily in animals and humans. In 2017, Delimont et al. compiled a number of studies around this topic.
In animals, the results are very contrasted, regardless of whether they are extracts of black or green tea polyphenols for example. On the other hand, when we look at the studies in humans, we can distinguish several interesting facts. Depending on the study carried out (a single meal, follow-up over several weeks, etc.), the results may be different. Indeed, the results seem to be more contrasted when the studies concern a single meal. In the follow-up of patients over several weeks, the majority of studies did not conclude that tea interfered with iron absorption. If we look at the studies that found decreases in iron in the body, they were of the order of 5%. In one of these studies, the patients already had anemia, which could indicate that the patients who were already anemic were more susceptible to tea.
Moreover, depending on the source of polyphenols used (extracts, condensed tannins, etc.) the effects may be different since several studies even observed an increase in iron absorption. In all the studies compiled, there was no anemia triggered by tea.
This recent compilation of human epidemiological studies is consistent with an older compilation (2004) from the UK. In the 35 studies analyzed, Nelson et al. demonstrated that daily tea consumption did not lead to the development of chronic anemia.
How to drink tea to avoid the risk of iron deficiency?
Health professionals recommend spacing tea consumption from meals. A study released in 2017 only confirms these recommendations. Indeed, Fuzi et al. showed that drinking tea one hour after a meal decreased iron absorption from tea by 50%. This can be explained by the fact that iron is rapidly absorbed in the intestines. It can be assumed that tea only absorbs a part of the iron from the food.
Tea decreases the absorption of iron, especially if the tea is drunk during meals, but it can also be dangerous if people already have anemia or if they have a background that favors its appearance (heredity, possibly a diet without animal products, use of food supplements for iron deficiency). To limit this negative effect of tea, it is necessary to space out the consumption of tea and the meal by at least one hour.
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