TEA AND ATHEROSCLEROSIS

Joe Vinson, Department of Chemistry
University of Scranton, Scranton, PA 18510, USA
E-mail: vinson@scranton.edu

 

 

Introduction

Tea is the most popular beverage in the world, except for water. The average per capita consumption is 110 ml [1]. Black tea accounts for 80% of the world's tea production [2]. When green tea is fermented, black tea is formed. This enzymatic oxidation reaction causes a shift from simple catechin compounds in green tea to more complicated polyphenols in black tea which gives black tea its characteristic color and taste. It is generally believed by the lay public and scientists alike that green tea is more beneficial to health since it contains more antioxidants, and it is well known that the Orient has less cardiovascular disease than the Western world.
The oxidative theory of atherosclerosis was proposed years ago [3]. Although antioxidant therapies have been shown to modulate atherosclerosis in experimental animals, similar monotherapies (vitamin E for example) have failed to show consistent clinical benefit in human trials [4]. However the clinical trials have involved adult subjects with atherosclerosis already present, since this disease starts early in life. As far as tea is concerned, no studies have yet been done to compare green with black tea.


Animal Studies with Tea

In reviewing the literature with animal models of atherosclerosis, one recurring variable has been the dose used. All are suprapharmacological, considering the weight of the animals compared to the dose. For instance, green tea given in the drinking water at 0.3% to cholesterol/high fat fed rabbits only slightly reduced atherosclerosis, while black tea was without effect. Both teas significantly decreased the oxidizability of LDL by 15% [5]. Green tea, in a concentrated extract (equivalent to > 50 cups/day for a human), significantly inhibited atherosclerosis in the Apo-E-deficient mouse [6].
Our group has used a cholesterol/saturated-fat-fed hamster model of atherosclerosis. Hamsters have similar lipid profiles to humans when given this regimen. We compared both green and black tea at two different concentrations in their drinking water: 1.25% (the usual human concentration), and 0.0625% (20-fold diluted) [7]. The diet was fed for 10 weeks when early atherosclerosis in the form of foam cells was present on the aorta. Animals fed a normal diet, with no added cholesterol or fat, were also given the two forms of tea. Interestingly in the normal groups drinking tea, significant improvements were found in the lipid profile, cholesterol, LDL, LDL/HDL, and triglycerides, especially with the high dose. Oxidizability of LDL+VLDL was decreased up to 15% with the high dose of teas. Both teas had similar effects. As expected in the control group fed cholesterol and fat, there was an increase in cholesterol, LDL, LDL/HDL, triglycerides, fibrinogen, and a decrease in the oxidizability of pooled LDL+VLDL oxidizability compared to the control group. Both teas significantly decreased the lipids. The lipoprotein oxidizability was greatly decreased by the teas, to the extent that it was equal to the normal control group. Teas at both doses significantly decreased foam cell coverage. There were significant correlations between cholesterol, LDL, LDL/HDL, lipoprotein oxidizability, fibrinogen, and atherosclerosis. There was no significant difference between green and black tea in this model. On a human dose basis, the low dose of tea in the study was equivalent to two 8-ounce cups of tea/day. Thus both green and black tea were found to improve the lipid profile in both normal and hypercholesterolemic animals. This is the first study to compare green and black tea and both were found to have equal benefit. Also this study is the first to show that tea causes an improvement in lipids and lipid oxidation parameters in normal animals.
Most recently an intriguing article has been published using epigallocatechin gallate (EGCG, the major catechin in green tea) in Apo-E-null mice with new versus established atherosclerosis in the same animals [8]. The dose given peritoneally was equivalent to about 5 cups/day. EGCG was able to significantly reduce recent cuff-induced atherosclerotic plaque but had no effect on the established lesions induced by hypercholesterolemia. The mechanism was hypothesized to be anitiproliferative and also antioxidative. This result emphasizes the preventive aspect of tea supplementation, specifically one of the ingredients in green tea.


Epidemiological and Interventional Human Studies

Numerous epidemiological studies show that tea consumption reduces the risk of stroke, myocardial infarction, and coronary heart disease. Meta-analysis of studies from 1966 to 2000 and those before 2001 show risk of these decreased with increased tea consumption in many regions of the world [9,10]. In a Dutch study that measured aortic atherosclerosis which was then followed for two to three years, the odds ratio for drinking 1-2 cups/day was 0.54. This decreased to 0.31 for > 4 cups/day [11]. The prevalence of myocardial infarction but not coronary artery disease was significantly decreased with increasing green tea intake in Japan [12]. In a U.S. study, long-term total and cardiovascular mortality were inversely associated with moderate tea drinking (< 2 cups/day) and heavy tea drinking (> 2 cups/day) compared to non-tea drinkers [13]. In a group of Japanese patients who underwent coronary angiography, green tea consumption (average 6 cups/day) was significantly higher in those without CAD than those with the disease (3.5 cups/day). [14]. The green tea consumption per day was an independent predictor for CAD in this study. A Saudi study also showed that consumption of 6 cups of black tea/day produced a 50% lower risk of CHD than 1 cup/day adjusted for all other risk factors. There was a positive dose-response reduction of CHD with tea drinking [15].
However, it is the intervention studies that persuade. There are both functional cardiac and lipid effects due to acute and long-term supplementation. In subjects with proven coronary artery disease, 450 ml of black tea either consumed once or twice daily for 4 weeks, improved endothelium-dependent flow-mediated dilation. Plasma antioxidant capacity also improved after long-term supplementation [16]. The results of this study were confirmed with a dose of 5 cups of black tea/day [17]. Although not an intervention study, this same group showed that black tea consumption was associated with lower diastolic and systolic blood pressure in older women [18]. Black tea, but not caffeine, acutely increased coronary flow velocity reserve in young healthy male subjects [19]. Two intervention lipid studies have used black tea. The first was a blinded placebo-controlled crossover study. Black tea (5 cups/day) was given to15 mildly hypercholesterolemic subjects on a Step-1 diet. Compared to the placebo this produced significant decreases in cholesterol and LDL without affecting LDL oxidation or plasma antioxidant capacity [20]. A much larger study, a double-blind placebo-controlled parallel-group trial at 6 clinics in China studied 240 mild to moderate hypercholesterolemic subjects on a low-fat diet for 12 weeks with a capsule which contained primarily black tea extract but also some green tea extract. Cholesterol, LDL, and HDL significantly decreased relative to the placebo with no adverse side effects [21]. A recent cross-sectional epidemiology study from Saudi Arabia confirmed the lipid effect of black tea. Women who drank more than 6 cups/day of tea had significantly lower plasma cholesterol than non-tea drinkers [22]. The only interventional study involving green tea was done in Portugal and reported at the European Atherosclerosis Society Congress. Four weeks of drinking 1 liter of green tea produced a significant reduction in total cholesterol, LDL, and apoB. Also beneficial was a significant increase in HDL and apoA-1. This was coupled with a decrease in lipid peroxidation and an increase in antioxidant capacity [23]. This was confirmed in a Japanese study where green tea consumption was associated with lower serum total cholesterol in healthy subjects [24].


Conclusion

It thus appears from recent work that teas have the potential to decrease the risk of coronary disease by a variety of mechanisms. There is evidence that a lifetime of drinking tea will have the most benefit. Both green and black tea are recommended as "healthy" beverages to be consumed both early and often for prevention of cardiovascular disease.

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