Lung carcinogensis in a rat model
Dr F L Chung

In this project Dr Chung studies the efficacy of black tea and caffeine on lung tumorigenesis induced by the tobacco carcinogen NNK in F344 rats. The investigation produced positive results. A lifetime tumour bioassay showed that black tea given in drinking water can inhibit the development of lung tumours in F344 rats treated with NNK. the tumour inhibitory effect is apparently due to the polyphenolic compounds in black tea such as theaflavins and theraubigins, and, to a significant extent, to the caffeine which is also present in tea. this is the first study of the contribution of black tea towards the prevention of lung carcinogenesis in rats. The results further strengthen the argument for thorough and targeted epidemiological studies to better define the role of tea in normal diet as a contributor to the prevention of lung cancer.

Tea and Oesophageal Cancer

Tea consumption is an independent determinant of oesophageal cancer risk
Hu J, Nyren O, Wolk A, Bergstrom R, Yuen J, Adami H O, Guo L, Li H, Xu X and et al. International Journal of Cancer Vol. 57 38-46 1994.

A hospital-based case-control study of oesophageal cancer was carried out in the Heilongjiang Province, a low-risk area for oesophageal cancer in China. From May 1985 to May 1989, 196 histologically confirmed cases and 392 controls with other (non-neoplastic) diseases were personally interviewed in the wards of 5 major hospitals. Information was obtained about usual consumption in the early 1980s of 32 major contributors to the diet in the province, socio-demographic status, smoking and alcohol consumption. Odds ratios (OR) were obtained from logistic regression models, and confounding was controlled by means of multivariate models. Smoking and alcohol consumption were major risk factors for oesophageal cancer in this population. Smokers of handmade cigarettes exhibited a particularly high risk. A near multiplicative synergism was found between smoking and alcohol consumption. There was a significant inverse dose-risk trend for combined consumption of vegetables and fruits; a 300-g increase per day lowered risk by 35%. Vitamin C intake was negatively associated with risk; a 100-mg increase per day lowered risk by 39%. Our data suggest a modifying effect of vitamin C and beta-carotene on risk associated with smoking, but the power of analyses was low. Salt, salt-preserved foods and pickled vegetables were not associated with increased risk. High temperature of meals and drinks was a strong risk indicator in this population. The strength of tea and overall tea consumption were independent determinants of the risk.

TEA AND CARDIOVASCULAR DISEASES

Tea Flavonoids and Cardiovascular Diseases: A Review

The LDT oxidative modification hypothesis of atherosclerosis, first postulated by Steinberg and colleagues (1991), has stimulated scientific interest in the potential of flavonoids from vegetables, wine and also tea to protect against CHD. Even a modest effect of tea on heart disease risk would be important from a public health point of view, because tea is the second most frequently consumed beverage in the world, and CVD is the most frequent cause of death in Western societies. Some prospective epidemiological studies have demonstrated lower rates of coronary heart disease in drinkers of black tea, but the evidence is not consistent.

Tea flavonoids possess various properties that may interfere with the process of atherogenesis. Tea components demonstrate strong antioxidant activity and inhibit LDL oxidizability in vitro. a number of tea components are absorbed (Hollman et al., 1997) but the evidence that tea consumption reduces LDL oxidation in vivo by increasing the intrinsic resistance of LDL to oxidation is inclusive. Furthermore it is not known whether the capacity of flavonoids to inhibit enzymatic and metalion catalyzed oxidative processes in vitro is relevant in vivo. Hypocholesterolemic activity of tea components has been suggested based on experimental animal and epidemiological findings. However, this could not be confirmed in short-term trials in humans.

Tea flavonoids possess a number of activities that may inhibit inflammatory processes in vitro, but the relevance for the in vitro situation is not clear as yet. Recent observations that ingestion of black tea and green tea reduces platelet aggregations in vivo indicate that flavonoids from tea play role in thrombotic processes in addition to or rather than in the early stages of atherogenesis. This could explain the observation in some epidemiological studies that tea intake is inversely associated with CHD mortality but not disease incidence. However, experimental data in man are as yet scarce.

The concept that tea intake may protect against cardiovascular disease has rested heavily on cellular and animal experiment that used conditions and/or concentrations unlikely to occur in man. More realistic studies in man have eliminated some hypotheses, such as that of a significant effect of black tea on serum cholesterol levels. However, the epidemiological studies definitively leave open the possibility that tea flavonoids have a beneficial effect on CHD and stroke risk. In view of the widespread consumption of tea, the effect of tea on CVD risk merits further exploitation. Such exploration should focus on studies in man or in animal models of proven validity.

April 1999, Research Shows Drinking Tea Reduces the Risk of Heart Attacks

A recent study published in the American Journal of Epidemiology and reported in The Lancet indicates that the risk of heart attacks in people who drank one, or more, cups of tea a day was about half that of those who drank no tea. Currently death rates from coronary heart disease in the UK are among the highest in the world with someone having a heart attack every two minutes.

Researchers from Boston who carried out the study looked at the tea and coffee drinking patterns of 340 men and women who had previously had heart attacks and compared them with a group of healthy people. The researchers suggested that the benefits of drinking tea may be attributed to the high concentration of flavonoids in tea which reduce blood clotting and the deposition of cholesterol in the blood vessels.

Several other research studies have also provided evidence about tea’s positive effect on heart disease: A Scandinavian study of men aged between 50-69 showed that drinking 4-5 cups of tea a day reduced the risk of stroke by 69% and other studies have indicated that drinking 4-5 cups of tea a day may also have a beneficial effect on high blood cholesterol and high blood pressure.

Dr Simon Maxwell, a Clinical Pharmacologist from Edinburgh University states: 'These exciting studies offer further information about the role that dietary flavonoids may play in reducing the risk of circulatory diseases'.