HUMAN EXPOSURE ASSESSMENT OF FLUORIDE FROM TEA (CAMELLIA SINENSIS L.) WITH SPECIFIC REFERENCE TO HUMAN BIOACCESSIBILITY STUDIES by Laura Chan

This study aims to determine the concentrations of fluoride in UK tea products andtheir infusions. This is related to the uptake and distribution of fluoride within teaplants Camellia sinensis (L.). Human oral bioaccessibility of fluoride from theconsumption of tea infusions was estimated, using an in vitro approach. The possiblehealth significance from fluoride exposure is discussed.Fluoride in tea products and the distribution within the tea plant was determinedusing a method, involving alkali fused digestion with ion chromatography and aconductivity detector for the instrumentation. For the aqueous infusions and thesupernatants in the bioaccessibility experiments, ion selective electrode with avoltmeter was adopted.Mean fluoride concentrations in tea products and their infusions varied significantly(p<0.001; n=3) and were related to the type of tea product and the retail cost. Thehigher priced teas, such as Darjeeling, Assam and Oolong, had lower fluorideconcentrations. The lower priced supermarket Economy ranged teas were significantlyhigher (p<0.05) in fluoride and exhibited concentrations similar to Chinese Brick tea,which is prepared using mature tea leaves. The higher quality products are preparedby selecting the finest tips of tea (buds), whereas an Economy products use coarserharvesting techniques to include mature leaves in the product.Fluoride affinity and tolerance of C. sinensis was assessed by a series of fluoride dosingexperiments, ranging from 0 to 200 mg. Following fluoride dosing, a rapid uptake andaccumulation occurred throughout the tea plants, resulting in partial necrosis ofrandom leaves. Despite the necrosis, the plants tolerated the fluoride and continuedto increase in height, although at a significantly slower rate (p<0.05) compared to thecontrol plants. Accumulation of fluoride was observed to be mostly in the matureleaves followed by younger buds, then the roots. This relates to the part of the plantivused to produce the tea types, with mature leaves for Economy products and the budsfor the finer teas.The in vitro bioaccessibility assessment of fluoride estimated that over 91.4% offluoride from a tea infusion is available in the human gastric compartment, with 92.1%in the gastro-intestinal compartment. The addition of milk reduced fluoride absorptionin the gastric and gastro-intestinal compartments to 73.8 and 83.1%, respectively,possibly reacting to form calcium fluoride. Despite the percentage bioaccessibility, theconcentration of fluoride available for absorption in the human gut was dependentupon choice of tea product. Based on an adult male, the findings suggest thatconsuming a litre of Economy tea can fulfil or exceed (75 to 120%) the recommendeddietary reference intake (DRI) of fluoride at 4 mg a day, but only partially fulfil (25 to40%) when consuming a more expensive Pure blend such as Assam.With regards to health, tea consumption is a source of fluoride in the diet and is highlyavailable for absorption in the human gut. Tea alone can fulfil an adult fluoride DRI,but is dependent upon choice of tea product. Excess fluoride in the diet can lead todetrimental health effects such as fluorosis of the teeth and skeletal fluorosis andconsuming economy branded tea can lead to a higher exposure.