Tea lowers the blood sugar level in hyperglycemic rats
Gomes A, Vedasiromoni JR, Das M, Sharma RM, Ganguly DK (1995): Antihyperglycemic effect of black tea (Camellia sinensis) in rat. J. Ethnopharmacol.45, 223-226.

Both Black and Green tea extracts were found to possess preventive as well as curative effects on streptozotochin-induced diabetes in rates. While green tea was more effective as a preventive, black tea was more effective as a curative agent. It was also found that tea treated animals overcame more easily the toxic effect of streptozotocin. It is suggested that the tea extracts possibly protect the B-cells of islets of Langerhans from the toxic effect of streptozotocin and also help regeneration of the damaged cells.

Black Tea enhances gastrointestinal motility
Chaudhuri L, Basu S, seth P, Chaudhuri T, Besra SE, Vedasiormoni JR, Das M, Ganguly DK (2000): Life Sc.66 (9), 847-854, Maity S. Vedaisiromoni JR, Chaudhuri L, Ganguly DK (2001): role of reduced glutathione 9GSH) and nitric oxide (NO) in black tea extract-mediated protection of ulcerogen induced changes in motility and gastric emptying in rat. Japan J. Pharmacol. 85,358-364.

Drug interaction (both in vivo and in vitro) studies suggest a cholinergic involvement and a partial role of prostaglandin and nitric oxide in the prokinetic effect of black tea on gastrointestinal motility.

Intestinal motility as well as gastric emptying were significantly reduced in rates treated with glutathione depleting agents. Prior oral administration of black tea extract for 7 days significantly increased the intestinal transit and gastric emptying with restoration of serum GSH level. Drug interaction studies provide evidence that nitric oxide may play a role in black tea mediated improvement of intestinal motility changes and gastric emptying induced by ulcerogen.

Black Tea inhibits tumour growth and inflammation
Das M, Sur P, Gomes A, Vedasiromoni JR, Ganguly DK (2001): Inhibition of tumour growth and inflammation by consumption of tea. Phytotherapy Research (in press).

The antitumour effect of tea was evaluated in the 3-methycholanthrene (3-MC) induced solid tumour model in mice. Tea extract favourably altered the changes in superoxide dismutase (a free radical scavenger) and the level of thiobarbituric acid reactive substance in the sera of mice. It also showed anti-inflammatory activity in the carrageenin-induced paw oedema in the rat.

Clinical Trial Project on Black Tea
Munsi K (1997): Studies on Diabetes Mellitus with special reference to the Effect of Black Tea in controlling Hyperglycemia and Hyperlipidemia. Doctoral (M.D.) thesis, Calcutta University.

A multicentric clinical trial project has been launched by TRA to evaluate the effect of Black Tea consumption on cholesterol and blood sugar level in diabetic and atherosclerotic patients.
Highly encouraging results on the beneficial effect of Black Tea consumption have been found in reducing Low Density Lipid (LDL) level in patient suffering cholesteromia. Significant results have also been obtained in reducing blood sugar level of non-insulin dependent diabetic patients by Black Tea consumption. Studies are currently being conducted to establish the relationship between the antidiabetic efficacy and level of tea consumption.

Tea and Oral/Dental Health

Black Tea adsorbs on human dental enamel
Sarkar S, Seth P, Chaudhuri T, Ganguly DK (2000): Effect of black tea on teeth. J. Indian Soc. Pedo. Prev. Dent.139.

The study has revealed a selective adsorption of black tea polyphenols by dental enamel. Theaflavin digallate and theaflavin gallates, polyphenolic constituents of Black tea, are adsorbed maximally whereas adsorption of catechins is lesser as compared to theaflavins. Caffeine was found to adsorbed negligibly. The adsorption of theaflavins to dental enamel may play a prominent role in inhibition of plaque formation.

Effect of black tea on caries in Hamsters
Dr Harald Linke and Dr Racquel Z LeGeros

The purpose of this study was to assess the effect of a standardised black tea solution on dental caries in a hamster model. They study used two variables: a standard laboratory chow diet or a cariogenic diet, and standardised black tea or deionised water. Throughout the experiments fluoride in the tea and in the water was monitored. Caries formation in the black tea group decreased by 56.6% (lab.chow diet) and 63.7% (cariogenic diet). However the fluoride content of the tea was higher than the water content and accordingly the different in caries formation may be a function of the fluoride or the polyphenolic content of the tea.

Evaluation of the effects of black tea on oral bacteria in vitro
Dr Philip Marsh

Tea extracts have been shown in laboratory studies to have inhibitory effects against a range of pathogenic microorganisms including viruses (e.g. influenza virus) and some bacteria (e.g. Staphylococcus aureus, Vibrio cholerae). In addition, earlier studies had shown that green tea or oolong tea extracts affect the composition, metabolism and pathogenicity of the oral microflora, but few studies have examined the antibacterial effects of black tea. The aim of this study was to investigate the effects of black tea extract (BTE) on a range of oral bacteria and on their metabolism, using a variety of in vitro test systems. Initially, a panel of more than 20 representative Gram-positive and Gram-negative oral bacteria were examined for their susceptibility to two concentrations of BTE. Next, the effect of BTE on defined mixed culture oral microbial communities was examined using continuous culture techniques. The sensitivity of biofilm and conventional liquid cultures was compared because oral bacteria grow on surfaces as biofilms (i.e. dental plaque), and biofilms are known to be more resistant to antimicrobial agents. Finally the inhibition by BTE of acid production from sucrose by streptococcus mutans (a principal causative agent of dental caries), and protease activity of Porphyromonas gignivalis (an abligately anaerobic bacterium implicated in advanced periodontal diseases), was also investigated. Bacteria grown in pure culture were inhibited only moderately by exposure to BTE for 1 hour. This exposure time was chosen to simulate more accurately the short contact times that are likely to occur in the mouth between antimicrobial agent and microorganism. At best, reductions in counts were <10-fold for any of the bacteria tested; in general, Gram-negative species were more sensitive than gram-positive species. Similarly, BTE showed only limited activity against themostat-grown communities of bacteria; no significant reductions were observed in the counts of individual bacteria in either liquid or biofilm phases of growth. However, there was insufficient time to determine whether repeated exposures to these extracts would result in accumulative inhibitory effects. Significantly, BTE inhibited the initial rate of acid production sucrose by S Mutans, with the effect still apparent after 90 minutes (two-way ANOVA, p<0.01). Low concentrations of BTE also showed a dose-dependent inhibition of the protease activity (p<0.00001) of P. gingivalis. Both of these metabolic properties are considered to be important virulence traits of these species. In conclusion, our studies suggest that BTE may have little direct effect on the microbial composition of dental plaque, but may exert subtle anti-metabolic activity against key pathogens that may reduce their disease potential.