As Green Tea, Black Tea and White Tea all come from the same plant, the health impacts of Fluoride ingestion from Green Tea discussed here are generally applicable.
Fluoride content of Green Tea
The highest Fluoride concentration reported in any vegetation occurs in tea leaves. The Fluoride content of Tea leaves can be 1,000 times the soluble Fluoride content of the soil and 2–7 times the total Fluoride content of the soil [Fung 1999]. A measurement of over 21,000 ppm was reported for one sample of black tea leaves [Michalski 2006].
Green Tea is produced from withered leaves that are steamed and rolled before drying to prevent the fermentation of the leaves, which occurs in making Black tea. Brewed Green Tea has been found to contain very high Fluoride levels, e.g. nearly 7 mg/L (ppm) when made with deionized water [Chan 2010] and over 25 ppm in one Green Tea brew [Lung 2003].
Brick Tea, made from older leaves, has even higher Fluoride content. Fluoride uptake is increased by the presence of Aluminium, probably due to the uptake of Aluminium–Fluoride complexes. Tea leaves are considered a hyper-accumulator of Aluminium. They can absorb up to 30,000 ppm of neurotoxic Aluminium [Matsumoto 1976, Shu 2003, Wong 2003].
Reports of the Fluoride content of Green Tea varies, with some finding lower Fluoride content than in Black Tea and others higher [Zerabruk 2010, Giljanović 2012, Zhu 2013, Embiale 2014, Atasoy 2016, Das 2017]. Given the Fluoride hazard, it is not surprising that the Tea industry has financially supported some research [Peng 2015].
Various assessments of Tea contribution to total daily intake have been reported [Pang 1992, Heilman 1999, Kao 2000, Malinowska 2008, Chan 2013, Peng 2015, Waugh 2016 ]. In temperate climates such as Britain excessive Tea intake was shown to contribute most to total intake of up to 8.9 mg of Fluoride per day [Walters 1983].
The pH of many brewed and bottled instant teas can be quite low [Simpson 2001, Behrendt 2002, Pehrsson 2011, Lunkes 2014, Reddy 2016] leading to a substantial amount of corrosive and cariogenic Hydrogen Fluoride (HF) in the beverage [Hendricks 2013]. Measurement of Fluoride content by ion selective electrode can be affected by particle size, brewing time, pH and Aluminium [Borjigin 2009] content, so that published values might in some cases represent underestimates of the toxicity hazard.
HF is not detected by a Fluoride ion selective electrode. Tactics used to improve analysis include the use of different ionic strength buffers including chelating agents for Aluminium such as tartaric acid, TRIS (tris(hydroxymethyl) methylamine), or trans-1,2-cyclohexanediamino N,N, N',N'-tetra acetic acid, and the use of the standard addition technique [Yuwono 2005, Reto 2008, Janiszewska 2013].
Ion chromatography using an alkaline eluant has been reported to be convenient for simultaneous measurement of anions present in Green Tea, which include Nitrate, Oxalate, Phosphate and Sulfate [Michalski 2006, Kumar 2008, Mincă 2013, Maleki 2016, Yang 2017].
Chewing gum incorporating Green Tea extract has been reported [Suyama 2011].
Harms associated with the Fluoride content of Green Tea
It is interesting that many studies alleging “benefits” of Green Tea completely avoid mention of the words Fluoride or Aluminium. It is also common to find reports dealing with the harms that avoid reference to Fluoride.
As has been pointed out many years ago [Schuld 1999], interpreting the literature on the effects of Green Tea is problematic because some papers consider a hot water extract as might be brewed from the dried leaves, others look at an aqueous ethanol extract, and some cover the swallowing of capsules containing either green tea powder or dried extract. Further complication arises because some researchers have reported on mixtures or pure isolated polyphenols from Green Tea.
Because Fluoride is a universal toxin that damages all types of mammalian cells, the list of harms from drinking Green Tea will follow those observed by Fluoride from drinking water [Pain 2017a] including cataract blindness [Pain 2017b]. The following discussion covers harms so far identified arising through drinking of Green Tea.
Animal studies
In test animal studies, Green Tea treatment-related mortality attributed to liver failure occurred in male and female mice at a dose of 1,000 mg/kg and changes were seen in both rats and mice in the liver, nose, mesenteric lymph nodes, thymus, Peyer’s patches, spleen, and mandibular lymph nodes [Chan 2010].
Skeletal Fluorosis and other Bone Disorders
The head of the Melbourne University Dental School in the state of Victoria, Australia, warned of the dangerous quantities of Fluoride in Tea in 1953, when industrial interests were planning to dispose of their waste through public drinking water supplies [Amies 1953].
The Australian National Health and Medical Research Council expressed its concern over the toxic levels of Fluoride in Tea in its meeting of 1954. In 1954, the NHMRC was most worried about skeletal Fluorosis which was widespread in Queensland farming communities using bore water as well as workers in hot conditions who consumed upwards of 10 litres of water per day, including up to 4 litres of Tea. Green Tea and isolated extracts from it are known to disrupt normal bone growth [Vali 2007, Isbel 2009, Iwaniec 2009].
Skeletal Fluorosis is a crippling condition affecting tens of millions of people [Li 2017] and habitual drinking of Tea is recognized as a major factor [Cao 1996, Cao 2005, Whyte 2005, Whyte 2008, Li 2009, Ge 2012, Kakumanu 2013, Chen 2014, Fan 2016, Yang 2016, Li 2017]. Due to instant-tea consumption, a patient developed severe skeletal fluorosis and had a serum Fluoride level of 7 µmol/L [Isbel 2010].
Osteopenia has been induced in mice fed Green Tea extract. Observed weight loss and failure to gain weight is consistent with lower femur length, volume, mineral content, cortical volume, cortical thickness, lower cancellous bone volume/tissue volume and trabecular thickness in lumbar vertebrae [Iwaniec 2009].
Allergy and acute adverse reaction
Double blind placebo testing has shown a percentage of people exhibit allergic reaction to Fluoride and it is possible that some Tea drinkers are unaware of the possible reactions, including heart arrhythmia, urticaria, exfoliative dermatitis, stomatitis, gastro-intestinal and respiratory allergy [Shea 1967].
Fluoride causes headache and migraine in some people so it is not surprising these ailments are experienced by some Tea drinkers [Seferoğlu 2012]. Green Tea affects the Thyroid and its hormones and can induce goiter [Schuld 1999, Sakamoto 2001, Chandra 2010, Abulfadle 2015]. Effects of Kombucha on mammal behaviour, as well as the organs, of test animals have been studied [Hartmann 2000].