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High Tea: High Risk?

​​Last week, I caught myself eavesdropping on a conversation between two elderly ladies in the train. One of their relatives was having issues with her bones and the doctor had said that the fluoride levels in her body were too high, for which excessive tea drinking was to be blamed. The story sounded pretty implausible to me and I supposed the lady recounting it was unintentionally giving a false representation of the doctor’s message. Somehow the story stuck with me and I decided to delve into it. One of the things I found, was a pretty recent research article on sources of fluoride intake in Ireland - including the consumption of black tea! - and their possible adverse health outcomes, among which skeletal fluorosis. When scanning through the article, I came across a section discussing the influence of fluoride intake during pregnancy. So let’s have a look.

​Something is Brewing

So what’s all the fuzz about? Who is blackening the black tea? Let’s start by saying that the fuzz isn’t discriminatory: it’s not just the black tea (like your English breakfast-tea, Earl Grey, Orange Pekoe or Brick tea), we are also talking about other types of tea that generally enjoy a healthy reputation, like green, white and Rooibos tea. And let’s not forget the products that contain tea, such as ice tea.

​​The fuzz is that tea plants are among those that easily absorb and stock fluorides that are present in air, soil and water. The amount of fluorides present in the tea plant can vary a lot between one place and another due to natural conditions and human activity. In the Ethiopian Rift Valley for instance, the water contains high amounts of fluoride released by basalt rocks, while in other places emissions by industrial plants or the use of pesticides can be the source of an increased fluoride level in the soil.

Tea leaves from the same plant do not necessarily contain the same amount of fluoride: as a rule, the more mature the leaves are, the more fluoride they contain when compared to younger leaves from the same plant. Besides, the level of fluoride depends on the place of origin of the leaves (natural concentration of fluoride in the soil), the way the leaves were cultivated (the use of pesticides and fungicides) and the way they were processed (fermentation time). Last but not least, you yourself also play a role in the amount of fluoride in your cup: the longer you let it brew, the more fluoride your tea is likely to contain.

The Fluoride Debate​​

In some areas, fluoride is added to drinking water in an effort to prevent tooth decay. For the same reason it is applied topically, for instance through toothpaste and dental care products. These days, some of these practices are disputed based on a supposed lack of scientific evidence. Fluoride can also be found in other products we use daily such as Teflon-coated cookware and in some medication. Furthermore it is set free when chewing tobacco, and is found in high concentrations in some wines and mineral waters.​​​​ In 2014, The Lancet was highly criticised when they published an article in which fluoride was added to the group of neurotoxicants that might play a role in neurodevelopmental disorders. The critics stated that at least some of the claims in the article lacked sufficient evidence. But the authors of the article weren’t the first ones to consider fluoride a toxin and to call attention to the possible harmful effects of fluoride intake. Over the years, concerned citizens have been asking questions about the use of and exposure to fluoride through, among other things, adding fluoride to drinking water and prescribing fluoride tablets in dental care.

To Absorb or Not to Absorb?

Sometimes, a distinction is made between calcium fluoride and sodium fluoride, with the former referred to as of organic origin and the latter as of synthetic origin (among which variations like fluorosilicic acid, sodium fluorosilicate, sodium fluoride). Whether this distinction actually matters with regard to the debate about possible toxicity, is subject to different opinions. In studies, this distinction is often even not made, but rather, bioavailability is used as a starting point. The bioavailability of fluoride in non-herbal tea is comparable to that of fluoride in drinking water, which is about 90%, since soluble fluoride is easily absorbed by the gastrointestinal tract of the human body. The bioavailability can be reduced however by consuming a lot of calcium. Now I am neither a chemist nor a toxicologist, but from what I read, I get that it is the ease with which a specific fluoride compound dissolves and the rate of absorption that plays a role. It is the digestion of water-soluble ionic fluoride that might affect the human health.

​​The Problem of Too Much...

​​Fluoride does not biodegrade and its accumulates both in the environment and in the human body. So even if we leave the toxicity debate aside, it will still be hard to define the exact fluoride levels in individual persons and the level of fluoride intake that might lead to the unwanted effect of fluorosis.

What we do know, is that in areas with a high amount of fluoride in drinking water, skeletal and dental fluorosis is endemic. Dental fluorosis is, in its mild form, a discoloration of the tooth enamel due to an excessive intake of fluoride in its formation phase. In its severe form, it can also damage teeth. Skeletal fluorosis is caused by an extreme accumulation of fluoride in bones, leading - it its more severe forms - to conditions like osteoporosis, hyperostosis, osteopetrosis and. In the above mentioned Ethiopian Rift Valley for instance, dental and skeletal fluorosis occurred so often, that ngo’s started a project for filtering the fluoride out of the water. In Tibet, researchers found a positive correlation between the consumption of brick tea and skeletal fluorosis. According to the researchers, there may be a causal relationship.

Tea for Two: Sipping Tea while Pregnant

Pregnant women are often showered with health advices to the point where they feel that everything is potentially harmful to their baby. After banning alcohol, energy drinks, coffee, coke and some herbal teas, should they now feel guilty for sipping non-herbal tea?

​​It seems clear that fluoride can pass from the mother’s blood to the foetus through the placenta, but the exact mechanism has not yet been defined. Some argue that the placenta is simply a gateway, while others think that it might actually block the spreading of fluoride. Still others have reported that the placenta only blocks fluoride diffusion when a critical level of fluoride intake has been reached.

Small scale studies have shown that fluoride can also pass the blood-brain barrier and accumulate in the foetus’s developing brain. More research into how this works is needed, but so far, some potentially adverse effects have been reported, for instance on the development of the central nervous system or the child’s bone health. It has also been reported that excessive intake of fluoride might have a negative impact on the course of the pregnancy itself, and a relation with an increased risk of miscarrying, giving birth prematurely and anemia has been suggested. Recent research on male mice suggests adverse effects on the quality of the semen.

The debate on the passage of fluoride into breast milk is ongoing. The American Centers for Disease Control mention that most infant formulas contain low levels of fluoride. When prepared with fluoridated water, they might increase the risk of mild dental fluorosis.

Better Safe than Sorry

Given all this, a high fluoride intake during pregnancy seems unadvisable. But what exactly is a high intake? In 2013, the European Food and Safety Authority wrote that the adequate intake of fluoride “from all sources (including non-dietary sources) is 0.05 mg/kg body weight per day for both children and adults, including pregnant and lactating women”. This “is based on the body weight before pregnancy and lactation”.​

​However, since according to the EFSA there are no reliable data on the amount of fluoride EU-citizens take on a daily basis, and the effects of fluoride on the pregnancy and the foetus remain unclear, ‘better safe than sorry’ seems the way to go. In practice, this means that moderating or even cancelling the consumption of non-herbal tea would be wise. If you really can’t give up your daily tea, it would be good to chose a high quality tea - that’s usually made of young leaves - from an area where fluoride concentration in the environment is low, and only let it brew for a short time.

In the mean while, initiatives such as the Cochrane review on ‘Fluoride supplementation in pregnant women for preventing dental caries in the primary teeth of their children’, which is currently being carried out and will also look into possible harmful effects, can only be cheered.

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Centers for Disease Control (2015). Overview: Infant Formula and Fluorosis. See:

Chan, L. et al. (2013). Human exposure assessment of fluoride from tea (Camellia sinensis L.): A UK based issue? Food Research International, 51(2): 564-70. Doi: 10.1016/j.foodres.2013.01.025

Diouf M. et al. (2012). Pregnant women living in areas of endemic fluorosis in Senegal and low birthweight newborns: case-control study [Femme enceinte vivant en zone de fluorose endémique au Sénégal et faible poids du nouveau-né à la naissance : étude cas–témoins]. Revue d'Epidémiologie et de Santé Publique, 60(2):103-8

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Waugh, D. et al. (2016). Risk Assessment of Fluoride Intake from Tea in the Republic of Ireland and its Implications for Public Health and Water Fluoridation. Int. J. Environ Res Public Health, 13(3): 259. doi: 10.3390/ijerph13030259 See:

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Zhipeng Fan et al (2016). Prevalence of Brick Tea-Type Fluorosis in the Tibet Autonomous Region. J Epidemiol. 26(2): 57–63. doi: 10.2188/jea.JE20150037 See:


Photo 1: CCBY Stephen Melling. See:

Photo 2: CCBY Dany13. See: Java West/Malabar Tea Estate/Harvest

Photo 3: CCBY Wikepedia

Photo 4: CCBY Textale Art Center. See:

Photo 5: CCBY Martinak15. See:

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