Q. 1: Are the findings in the study accurately reflected in the article?
In the study, as described on Food Research International: Human exposure assessment of fluoride from tea (Camellia sinensis L.): A UK based issue?, they measured the amounts of fluoride in various teas and then only commented (not investigated) their possible side effects as described in other studies; for example, they said that some cheap teas on the UK market have fluoride contents comparable to "brick tea," which was associated with many cases of dental and skeletal fluorosis in China. The article also mentioned a possible association between cheap teas and cancer.
The article on Natural News: Cheap tea bags contain frighteningly high fluoride levels: Study made an abstract of the study article and actually presented the possible side effects of tea in less dramatic way than the original article.
Q. 2 and 3: Are the findings in the study corroborated by other studies, or contradicted? Is the study's methodology sound?
One author in Nutrition Bulletin, 2014 questioned the method used to measure fluoride in tea in said study, but he did not prove it wrong. The researchers from Medical College of Georgia/US have found similar levels of fluoride in some black teas (Science Daily, 2010), so, the data in the UK study seems plausible.
The summary of evidence from studies:
- In the mentioned UK (and other studies), they have found up to 9 mg fluoride per liter of some cheap teas.
- Adverse effects of excessive fluoride intake can include:
- Dental fluorosis due to fluoride intake as low as 1 mg/day before age 8
- Skeletal fluorosis after fluoride intake >10 mg/day for at least 10 years
- In the US and UK, there have been only sporadic cases of severe dental or skeletal fluorosis documented and most of them have been associated with the consumption of >20 mg fluoride, usually due to drinking " a gallon" or more tea daily for more than 2 decades.
- In China, drinking about 2 liters of tea with total daily consumption ~12 mg fluoride/day for decades (but in children only for few years) has been associated with many cases of dental and skeletal fluorosis.
The amount of fluoride in tea
According to the study in the UK, 2013:
Fluoride concentrations in UK tea, including the leading supermarket
economy labelled products, were determined. Fluoride ranged from 93 to
820 mg/kg in the products and 0.43 to 8.85 mg/L in the infusions.
Amount of fluoride (in mg/liter) in various types of tea after brewing for 2 minutes in deionized (non-fluoridated) water (Table 3):
- Economy blends (Tesco Value bags 1): 3.60-7.96
- Black blends (PG Tips bags): 0.76- 4.98 mg
- Green blends (Clipper Organic leaf): 1.62-4.32
- Pure blends (Asam leaf): 0.71-2.5 mg
- Oolong (Luk Yu Oolong): 0.43-1.43 mg
The fluoride content is highest in cheap teas, because they contain more mature tea leaves. Other black and green teas can also contain a lot of fluoride, but herbal teas usually only little.
Data about fluoride in teas from other studies (fluoride/liter tea):
Safe fluoride intake levels
According to The National Academies, 1997, in the US, the Tolerable Upper Intake Level (UL) for fluoride (the amount that should not cause any side effects except mild dental fluorosis) is:
- 0-6 months: 0.7 mg/day
- 7-12 months: 0.9 mg/day
- 1-3 y: 1.3 mg/day
- 4-8 y: 2.2 mg/day
- 9 y and older: 10 mg/day
1) Dental fluorosis refers to yellow discoloration of the permanent teeth due to excessive fluoride intake until age 8, but not later (The National Academies, 1997):
The preeruptive maturation of the crowns of the anterior permanent
teeth is finished and the risk of fluorosis is over by 8 years of
age (Fejerskov et al., 1977). Therefore, fluoride intake up to the
age of 8 years is of most interest. Several reports suggest that
enamel in the transitional or early maturation stage of development is
most susceptible to fluorosis, which for the anterior teeth, occurs
during the second and third years of life.
...milder forms of enamel fluorosis affected the permanent teeth
of 10 to 12 percent of permanent residents in communities where
the drinking water had a fluoride concentration close to 1.0
mg/liter. The fluoride intake of children with developing teeth in
these communities averaged 0.05 mg/kg/day and ranged from 0.02 to 0.10
mg/kg/day...Mild enamel fluorosis affected about 50 percent of
residents where the water contained 2.0 mg/liter of fluoride. At
this concentration, a few cases (< 5 percent) of moderate fluorosis
were recorded (Dean, 1942). Fluoride intake by most children in these
communities would have ranged from approximately 0.08 to 0.12
mg/kg/day. An average, chronic daily fluoride intake of 0.10 mg/kg
appears to be the threshold beyond which moderate enamel fluorosis
appears in some children. Where the water fluoride concentration was
4.0 mg/liter, nearly 90 percent of the residents had enamel fluorosis, and about one-half of the cases were classified as moderate or severe.
2) Teeth with mild fluorosis appear to be more resistant to caries:
Fluoride and Dental Caries Prevention in Children (California Dental Association, 2014):
Almost all fluorosis in the United States is very mild or mild (Figure
4); (44) teeth with this degree of fluorosis are more resistant to
caries than teeth without fluorosis. More severe dental fluorosis,
which manifests as enamel pitting and predisposition to staining
(Figure 3D), is unusual in the United States but occurs in other parts
of the world where there are naturally high levels of fluoride in the
water (eg, >2 ppm). Teeth with severe fluorosis are paradoxically
more susceptible to caries.
3) In one small 1996 study in Tibet, more than 50% of children who have consumed about 5.5 mg fluoride/day, mainly by brick tea, had dental fluorosis.
Skeletal fluorosis refers to skeletal pain and deformities due to increased bone mass caused by high fluoride intake. According to The National Academies, 1997:
an intake of at least 10 mg/day for 10 or more years is needed to
produce clinical signs of the milder forms of the condition.
1) The article Skeletal fluorosis and instant tea (The American Journal of Medicine, 2005) describes a case of a 52-years-old woman who developed skeletal fluorosis after drinking 1-2 gallons (4-8 liters) of instant tea prepared with fluoridated water for about 30 years (estimated fluoride intake: 37 to 74 mg/day).
2) In another article: Skeletal Fluorosis From Instant Tea (The Journal of Bone and Mineral Research, 2009), a 49-year-old woman, who was drinking 2 gallons (~8 liters) of instant tea with 5.8 mg fluoride/liter from age 12 (estimated fluoride intake: 44 mg/day.) has developed skeletal fluorosis.
3) In a study in Tibet/China: Brick tea fluoride as a main source of adult fluorosis, Food and Chemical Toxicology, 2003, most adults who were habitually drinking "brick tea" (average fluoride intake: 12 mg/day) had some osteosclerosis or arthritis.
4) In another study in Tibet Prevalence of Brick Tea-Type Fluorosis in the Tibet Autonomous Region (Journal of Epidemiology, 2016), 18-84 % of adults who were regularly drinking brick tea had skeletal fluorosis.
In the studies in Saudi Arabia, 2010, the UK, 2012/13, Ireland, 2016, Canada, 2018, India, 2018 and Iran, 2018 they have observed an association between modest fluoride intake by tea and fluoridated water and hypothyroidism, especially in the individuals with iodine deficiency, but more research is warranted.
I have found no studies about fluoride in tea and cancer, but according to Agency of Toxic Substances and Disease Registry, 2013, there is no association between high fluoride intake from water and cancer:
Most of the studies of people living in areas with fluoridated water
or naturally high levels of fluoride in drinking water did not find an
association between fluoride and cancer risk.
- Dental fluorosis (yellow discoloration of permanent teeth) can develop in children under age 8 who regularly drink tea with as little as 1 mg fluoride/liter. Mild fluorosis decreases, but severe fluorosis (>2 mg fluoride/day) increases the risk of caries.
- Skeletal fluorosis (increased bone density with skeletal pain or deformities) can develop in adults who start to drink tea as children or adults and consume at least 10 mg fluoride/day (for example 2 liters of tea with 5 mg fluoride/liter) for at least 10 years. Drinking 1 liter of tea with the highest fluoride level in the UK study (8 mg/liter) should not have any side effects in adults. Skeletal fluorosis in the US and UK is extremely rare.