A single dose of tea with or without milk increases plasma antioxidant activity in humans
R Leelan, AJC Roodenberg, LBM Tijburg & SA Wiseman, European Journal of Clinical Nutrition, 2000, 54: 87-92

Objective: To investigate the effect of black and green tea consumption, with or without milk, on the plasma antioxidant activity in humans.

Design: In a complete cross-over design, 21 healthy volunteers (10 male, 11 female) received a single dose of black tea, green tea (2g tea solids in 300ml of water) or water with or without milk. Blood samples were obtained at baseline and at several time points up to 2h post-tea drinking. Plasma was analysed for total catechins and antioxidant activity, using the ferric reducing ability of plasma (FRAP) assay.

Results: Consumption of black tea resulted in a significant increase in plasma antioxidant activity reaching maximum levels at about 60 min. A larger increase was observed after consumption of green tea. As anticipated from the higher catechin concentration in green tea, the rise in plasma total catechins was significantly higher after consumption of green tea when compared to black tea. Addition of milk to black or green tea did not affect the observed increases in plasma antioxidant activity.

Conclusions: Consumption of a single dose of black and green tea induces a significant rise in plasma antioxidant activity in vivo. Addition of milk to tea does not abolish this increase. Whether the observed increases in plasma antioxidant activity after a single dose of tea prevent in vivo oxidative damage remains to be established.

Black and green tea exhibit antioxidant activity.
Goldbohm, R.A., Hertog, M.G., Brants, H.A.M., van Poppel, G. and van den Brant, A., European Journal of Clinical Nutrition Vol. 50 28-32 1996

Objective: Evaluation of the in vitro antioxidant activity of green and black tea, their in vivo effect on plasma antioxidant potential in man and the effect of milk addition.

Design: The antioxidant activity of the tea, with and without milk, was tested in vitro by measuring the length of peroxyl radical induced lag-phase. The in vivo activity was tested on two groups of five healthy adults. Each group ingested 300 ml of either black or green tea, after overnight fast. The experiment was repeated on a separate day, adding 100 ml whole milk to the tea (ratio 1:4). Five subjects acted as controls. The human plasma antioxidant capacity (TRAP) was measured before and 30, 50 and 80 mins. from the ingestion of tea.

Results: Both teas inhibited the in vitro peroxidation in a dose-dependent manner. Green tea was sixfold more potent than black tea. The addition of milk to either tea did not appreciably modify their in vitro antioxidant potential. In vivo, the ingestion of tea produced a significant increase of TRAP (P <0.05), similar in both teas, which peaked at 30-50min. When tea was consumed with milk, their in vivo activity was totally inhibited.

Conclusions: The paper shows that tea possesses a strong antioxidant activity in vitro, which is believed to be exerted by its polyphenols moiety. It also provides compelling evidence that tea has also a potent in vivo activity in man. The promptness of the in vivo response suggests that the absorption of the bioactive components of tea take place in the upper part of the gastrointestinal system. The inhibition of this effect by milk is thought to be due to the complexation of tea polyphenols by milk proteins. These findings might help to clarify the putative role of dietary polyphenols in modulating oxidative stress in vivo.

Sponsorship: This work was funded by the National Research Council (Italy) Project RAISA, Subproject 4, Paper no. 2326.

Antioxidant Capacity and Polyphenolic Components of Teas: Implications for Altering in Vivo Antioxidant Status1
Ronald L Prior*2 and Guohua Cao*, US Department of Agriculture* Agriculture Research Service, Jean Mayer Human Nutrition Research Center on Aging of Tufts University, Boston, Massachusetts 02111; and Nutritional Science Department, University of Connecticut, Storrs, Connecticut 06269

The Oxygen Radical Absorbance Capacity (ORAC) assay was used to determine the total antioxidant capacity of tea. Green and black teas (n=18) had a mean antioxidant capacity of 761.1 * 85.3 pmol Trolox Equivalents (TE) per g dry matter. However, their antioxidant capacity varied from 235 pmol to over 1526 pmol Trolox equivalents (TE)/g dry matter, and total phenolics ranged from 32 to 147 mg/g in different commercial teas. One tea phenolics extract had an antioxidant capacity of 4796 mumol TE/g dry matter and 625 mg total phenolics/g. On a dry matter basis, an antioxidant capacity of 761 mumol TE/g is considerably higher than any of the other fruits and vegetables measured in our laboratory. However, since dry tea is not consumed directly, brewing conditions may influence the final antioxidant capacity in the tea as consumed. We tested both green and black teas by placing one tea bag (1.95 g) in 150 ml (5 oz.) of boiling water. In the first brewed cup, approximately 84% of the total antioxidant activity was solubilized within the first 5 min. of brewing. An additional 13% of the antioxidant activity was extracted into the second glass of 150 ml with an additional 5 min of brewing. At the dilutions obtained after the first brewing, the tea as consumed would contain approximately 8.31 pmol TE per ml. This total antioxidant capacity compares to other drinks from fruits and vegetables that had antioxidant capacity values ranging from 1.6 to 15 pmol TE/ml. At these antioxidant levels, consumption of 150 ml of tea could make a significant contribution to the total daily antioxidant capacity intake. (-)-Epicatechin and (=)-catechin, two components from tea, had an antioxidant capacity of 2.36 and 2.49 pmol/pmol or 8.13 and 8.58 pmol/mg, respectively. In 16 tea samples we observed a mean of 10.0 * 0.6 pmol TE/mg total phenolics. Tea can be an important source of what has been referred to as “non nutrient” antioxidant phytochemicals. However, with the variation that exists in antioxidant capacity with various tea preparations, measures of antioxidant capacity intake are critical to the study of intake and health outcomes and/or biomarkers of health outcomes.

TEA & CANCER

A Barrier to Cancer?
John Weisburger, PhD

Whether tea really helps prevent cancer is still under debate, but research in its favour is piling up. In one of the largest studies to date, Iowa researchers found that tea may be a powerful cancer fighter, according to a study published in the July 1996 issue of the American Journal of Epidemiology. The study of more than 35,000 postmenopausal women showed that those who drank at least two cups of black tea a day were 40% less likely to develop urinary tract cancer and 68% less likely to develop cancer in the digestive tract than women who did not drink tea.
Other research shows that tea may be a promising weapon in the fight against cancers of the stomach, bladder, oesophagus, and prostate. Moreover, a study in China concluded that smokers who drink tea have a lower incidence of lung cancer, Weisburger noted in an April 1999 summary of the Second International Symposium on Tea and Human Health.

If tea indeed reduces cancer risk, it may be because its polyphenols pack a three-part punch. First, they prevent free radicals from damaging DNA, nipping cancer initiation in the bud. Second, they seem to prevent uncontrolled cell growth, slowing cancer development. And third, certain polyphenols may even destroy cancer cells without harming the surrounding healthy cells. When Japanese researchers combined cancer medications with polyphenols, the treatment was 20 times more effective than the cancer drugs alone, according to a study published in the March 1998 issue of the Japanese Journal of Cancer Research.