Excessive lipid induces obesity. This is a physiologically abnormal phenomenon in modern society. Obesity is closely related to excessive serum lipid. Experiments show that tea drinking plays an obesity-depressing role via an increase of fundamental metabolic rate and the degradation of fat. Investigations carried out by French, Japanese and Chinese scientists have also shown that Pu-Er tea and Oolong tea possess a significant obesity depressing effect (). Researches using different kinds of tea revealed that the serum lipid depressing and obesity depressing effects of compressed tea was greater than that of green tea and black tea ().
High levels of blood cholesterol induce the deposit of lipid on the vessel wall and cause the constriction of coronary arteries, atherosclerosis and thrombus formation. It is related to the fact that tea drinking decreases the serum lipid and cholesterol level. In the past, atherosclerosis was thought to result from a level of serum cholesterol above 200dl and a relatively low level of high-density cholesterol and high level of LDL. Current views are that it is induced by the oxidation of low-density cholesterol cholesterol that leads to foci of endothelial abnormalities associated with the process of atherosclerosis (). Te a and tea polyphenols possess the ability to prevent the oxidation of low-density cholesterol cholesterol () and anticoagulation of blood platelets and anti-atherosclerosis effects (). From the viewpoint of hemorheology, a high hemagglutination situation favors thrombus formation. Research on 120 patients with hyperlipidemia also found that tea pigment (tea polyphenols and their oxidative products are the major components), catechins, thearubigin (TR) and theaflavin possess anticoagulation and antihemagglutination activity, and the ability to promote fibrinolysis, indicating a therapeutic effect on the atherosclerosis (). Scientists from China also showed that Oolong tea drinking decreased the viscosity of blood. Newly emerging data suggests that those blood lipids that have previously undergone oxidation may be more likely to promote the development of atherosclerosis. Hence, inhibition of fat oxidation, either in vitro or in vivo, may reduce the risk of developing atherosclerosis and ultimately cardiovascular diseases (). Epidemiological studies showed that individuals consuming four or more cups of tea per day have a lower risk of atherosclerosis and coronary heart disease (). Tea also showed a certain degree of efficiency in the control of coronary heart diseases. According to a survey of coronary heart disease in the population of a tea growing area by Zhejiang Medical University in China, the coronary heart disease percentage in the population who drank no tea or occasionally drank tea was on average 5.7%, and that in the population who frequently drank tea averaged 1.07%, that was one-fifth of the above group. There were some prescriptions used in the control of coronary heart disease in Chinese traditional medicine. For example, the extracts of old tea plant root with glutinous rice wine was effective in curing the coronary heart disease. As mentioned above, tea polyphenols showed antioxidative activity (), thus suggesting a role in the prevention of atherosclerosis.
Namiki et al. () carried out an investigation on the inhibitory effect of hot water extracts prepared from various kinds of tea and catechins on platelet aggregation induced by collagen by using turbidimetry. Results showed that Japanese steamed tea and Kenya black tea possessed strong inhibitory activity (more than 50%) on the aggregation of blood platelets. Among the 6 catechins and 3 TFs as well as caffeine, (-)-EC, (+)-C, (+)-GC and theaflavin monogallate showed a marked inhibitory activity (). A compound of 4-hydroxy angular furocoumarin was isolated from the tender leaves of tea plant and showed an anticoagulating property of blood (). An inhibiting effect of a hot water extract of green tea on collagen-induced aggregation of washed rabbit platelet was shown and suggested the catechin and EGCG were the most active components (0.45 mM). This potency is in a comparable range to aspirin. Thrombin- and PAF-induced aggregation was also shown to be inhibited by EGCG (). A further experiment showed that ECG and EGCG were found to be more potent inhibitors for thrombin by mode of noncompetitive inhibition. The 50% inhibition of thrombin amidolysis by ECG and EGCG were 1.2×10-6 M and 1.1×10-6 M and of fibrin formation were 2.5×10-5 M and 5.8×10-6 M, respectively (). It is regarded that the aggregation of blood platelets was related to the activity of proteinases in fibrinolysis and kallikrein-kinin systems (). Research showed that the ester type catechins (ECG and EGCG) are more potent inhibitors to those enzymes in the fibrinolytic and the kallikrein-kinin systems, thus showing the ability to prevent thrombosis and thrombolysis (). Ali et al. () isolated a potent thromboxane formation inhibitor from fresh tea leaves. A further investigation identified the active compound as 2-amino-5-(N-ethylcarboxyamido)-pentanoid acid. It has the same chemical structure as theanine, just a different nomenclature system. It is apparently unique to tea when fed orally to mice or rats for eight weeks, a significant in vivo diminution in thromboxane level was measured in the serum. The black tea did not produce this effect. It was a potent inhibitor of thrombin-stimulated thromboxane formation in rabbit whole blood. The inhibitory activity was 100 times higher than that of caffeine (). A concentration as low as 50 µM suppresses thromboxane formation by 84% ().
Imai et al. () have conducted epidemiological investigations on the relationship between tea drinking and cardiovascular disorders in Saitama region since 1986. In total, 8553 inhabitants aged over 40 years old were surveyed, the blood samples from 3625 inhabitants were collected and 36 items including total serum cholesterol, HDL, LDL, neutral lipid were analysed. The investigated people were divided into three groups according to the number of cups of green tea (<3 cups/day, 4-9 cups/day and >10 cups/day). Results showed that the total serum cholesterol, neutral lipids, and the atherosclerosis index were decreased with the increasing of amount of tea drinking. It is also interesting that the average value of peroxidized lipid in smokers who drank more green tea was lower than that in those who drank less. The peroxidized lipid value was 9.1, 9.0 and 8.5 nmol/ml in<3 cups, 4-9 cups and>10 cups/day Results showed that for the green tea, the more drunk, the less cardiovascular disorders occur (). An epidemiological investigation among 5910 non-tea drinking and non-smoking women (>40 years of age) was conducted in Sendai city, Taijiri and Wakuya villages in Miyagi region in Japan. The medical history of strokes was less frequently observed among those who consumed more green tea. These populations were followed for four additional years and the incidence of stroke and cerebral hemorrhage was two to three times lower in those who drank more green tea (5 cups was the dividing line) (). A cohort of 552 men aged 50 to 69 years old was selected in 1970 and followed up for 15 years for the epidemiological survey on dietary flavonoids and the incidence of stroke. During the 15 years of follow-up, 42 first fatal or nonfatal strokes occurred in 552 men. Results showed that dietary flavonoids including tea consumption were inversely associated with stroke incidence. The relative risk of the highest vs the lowest amount of flavonoids intake (>28.6 mg/d vs<18.3 mg/d) was 0.27 (0.11 to 0.70). In the Nertherlands, it was regarded that black tea contributed about 70% of the flavonoid intake. The relative risk for a daily consumption of 4.7 cups of tea vs less than 2.6 cups of tea was 69% reduced risk of stroke ().
Thus, it can be concluded that the possible mechanisms for the antiatherosclerosis effect of tea drinking can be explained as follows: 1. Reducing plasma lipid and cholesterol formation (); 2. Elevating the high-density cholesterol (HDL) level in plasma (); 3. Inhibiting the cell’s absorption of lipid as well as accelerating the elimination and decomposition of the cholesterol that had deposited on the artery wall (); 4. Improving the hemorheological state and microcirculation of blood as well as reducing thrombosis (); 5. Decreasing the viscosity of blood and prolonging the coagulation time of blood platelets as well as increasing the blood fluidity (); 6. Antioxidative activity on blood lipids (); 7. Inhibiting the enzymes in the fibrinolytic and the kallikrein-kinin system ().
Selections from the book: “Tea: Bioactivity and Therapeutic Potential”. Edited by Yong-su Zhen, Zong-mao Chen, Shu-jun Cheng, and Miao-lan Chen. Series “Medicinal and aromatic plants – industrial profiles”. 2002.