BBCi News reported in May 2003 that "Herbal tea damages teeth". The article stated that research suggested dentists who treat patients with tooth erosion should advise them against drinking tea. The article also presented quotes from a spokesman for Twinings (leading herbal tea UK manufacturer) rejecting the claims. The research study was reported in the Journal of Dentistry.
Where does the evidence come from?
The study was undertaken by Judith Phelan and Jeremy Rees from the division of restorative dentistry, University of Bristol Dental School: The erosive potential of some herbal teas. Journal of Dentistry 2003; 31(4): 241-246.
What were the authors' objectives?
To screen a number of herbal tea products for their potential to cause dental erosion. The authors sought to compare a number of commercially available herbal teas and compare these with traditional tea, water, and orange juice.
What was the nature of the evidence?
The study was an in vitro study to test the erosive potential of a variety of herbal teas and compare these with traditional tea, water and orange juice.
What interventions were examined in the research?
The teas tested were:
- Lift instant tea
- Echinacea and raspberry
- Blackcurrant, ginseng and vanilla
- Raspberry, cranberry and elderflower
- Camomile
- Traditional blackcurrant
- Traditional lemon
- Peach and passionfruit
- Lipton ice tea (lemon)
The erosive potential of these products were assessed in the laboratory by measuring their pH (using an electronic pH meter), neutralisable acidity (by measuring how much 0.1M sodium hydroxide solution was needed to neutralise the tea sample) and their ability to erode enamel (using profilometry). These were compared to the positive control orange juice.
All herbal 'bag based' tea drinks were produced using a standard method: one teabag was added to 250ml of fresh boiling water and stirred at 0.2.4 and 5 min then the bag was removed. The solution was cooled until it reached 37°C before testing. The non-bag products (Lipton Ice tea and Lift Instant Lemon tea) were prepared using manufacturers' instructions.
What were the findings?
The pH of the teas ranged from 3.15 to 7.08 compared to 3.73 for orange juice. The traditional black tea and camomile tea were significantly more alkaline than the other teas (p<0.001).
The neutralisable acidity values ranged from 3.45ml for traditional black tea to 60.3ml for the Lipton Ice Tea Lemon. The neutralisable acidity value for orange juice was 21.4 ml. The neutralisable acidity of the traditional tea was significantly lower than all of the herbal teas, apart from camomile tea (p<0.001). Lift Instant Tea and Lipton Ice Tea had a significantly higher neutralisable acidity than the other herbal teas (p< 0.001).
The amount of enamel lost following immersion in the drinks ranged from 0.00 to 9.6 micromillimeters. Compared to the traditional tea, camomile and water, the enamel loss caused by all other teas was significantly higher (p<0.00). When the enamel erosion caused by the teas was compared with that for orange juice it was found tat the following teas caused significantly greater erosion:
- Blackcurrant, ginseng and vanilla
- Raspberry, cranberry and elderflower
- Raspberry, strawberry and loganberry
- Traditional blackcurrant
- Peach and passionfruit
- Lipton Ice Tea (lemon)
What were the authors' conclusions?
The authors concluded that many of the herbal teas tested were more erosive than orange juice and that this information will be of use to clinicians when counselling patients with tooth surface loss.
How reliable are the conclusions?
The research was an in vitro laboratory study, and the results should be interpreted with caution. The measurements of enamel erosion by the various drinks does not represent a real life situation in which other factors will affect the erosion: the flushing and remineralising effects of saliva, and that the enamel surface in a clinical setting would be covered in a protective pellicle/plaque layer.
Additionally the types of teas being tested were misrepresented in this research. Most of the teas were fruit infusions, which would be expected to have a high pH and neutralisable acidity. However the research formulates conclusions on the erosive potential of herbal teas. The only herbal infusion tested was camomile tea which was found to be significantly more alkaline than other teas and was so close to neutrality that it proved impossible to measure the neutralisable acidity, or to measure the amount of enamel erosion that it caused.
Systematic reviews
No systematic reviews relevant to this topic were found.
How did the media report the study findings?
The newspaper article followed the research paper quite closely but did not report the authors discussion on the need for caution when interpreting the results. The article did not go into any detail about the range of teas tested and did not mention that most of the samples were fruit infusions not herbal teas.
Links to the relevant, available news articles
BBC news 3 May 2003: Herbal tea damages teeth
