Tea drinkers who opt for cheaper supermarket blends could be at a higher risk of bone and teeth problems, researchers, including an Indian origin scientist, have claimed.
Many supermarket value brands have been found to contain potentially harmful levels of fluoride - a mineral that can severely damage bones if consumed in large amounts, researchers said.
Levels of fluoride found in 38 tea products were compared with each other and to the US National Academy of Sciences' (NAS) daily dietary reference intake in the research by Laura Chan, Professor Aradhana Mehra and Professor Paul Lynch from the University of Derby London.
Using Ion Selective Electrode (ISE) analysis - which can analyse trace elements, such as fluoride, in a liquid - of the dry tea, and of the tea infusions brewed with boiling water for two minutes, the researchers compared the fluoride levels ingested by someone drinking the average daily intake of tea (four cups or one litre).
Significant differences in fluoride levels were discovered when economy black tea blends from supermarkets Asda, Tesco, Morrisons and Sainsbury's were compared with branded black tea blends such as PG Tips, Twining's, Typhoo; and with green tea blends including Clipper Organic leaf, Green Twining's bags and pure blends.
Infusions of economy black tea blends, such as Asda Smartprice, Tesco Value, Morrisons Value, Sainsbury's Basics, and Waitrose Essential, were found to have the highest concentration of fluoride - an average of six milligrammes (mg) per litre.
Although, Waitrose Essential was significantly lower in fluoride compared to the other economy black blends.
When compared to the NAS daily dietary reference intake of four milligrammes of fluoride per day, these economy blends of tea contained from 75 per cent to 120 per cent of the recommended daily intake.
Infusions of green tea blends had the next highest concentrations, followed by branded black blends such as PG Tips, Twining's and Typhoo with an average of 3.3 mg per litre, then pure blends.
Oolong and Pu'er teas had the lowest concentrations of fluoride - an average of 0.7 mg/litre or just ten per cent to 16 per cent of the daily reference intake.
"Although fluoride is considered an essential micro-nutrient for human health, in the prevention of tooth decay and promotion of healthy bone growth, excess fluoride in the diet can have detrimental effects. Dental fluorosis, the mottling of tooth enamel, and skeletal fluorosis, pain and damage to bones and joints through calcification, can occur," said Chan.
The study was published in journal Food Research International.