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Miura et al., conducted an experiment, to examine the intake of green tea polyphenols renders LDL resistant to ex vivo oxidation in humans male volunteers were assigned the same dietary pattern. They were equally divided into two groups: control and tea. The tea group ingested 300 mg of green tea polyphenol extract twice daily. Plasma concentrations of lipids, ascorbate, α-tocopherol, and lipid peroxides did not change before and after the experiment in either group, but β-carotene was higher in the tea group. These results suggested that daily consumption of seven to eight cups (approximately 100 mL each cup) of green tea might increase resistance of LDL to in vivo oxidation, leading to lowering the risk of cardiovascular diseases.
Erbaet al., (2005) investigated the effect of the addition of two cups of green tea (containing approximately 250 mg of total catechins) to a controlled diet in a group of healthy adults with respect to a group following the same controlled diet but not consuming green tea. Antioxidant status and lipid profile in plasma were measured at the beginning and at the end of trial. Consumption of GT caused a significant increase in plasma total antioxidant activity, significant decreases in plasma peroxides level and induced DNA oxidative damage in lymphocytes), a moderate although significant decrease in LDL cholesterol with respect to control. The study suggested the ability of GT, consumed within a balanced controlled diet, to improve overall the anti-oxidative status and to protect against oxidative damage in humans.
Zaveri, (2005) reported that the use of green tea as a cancer chemo preventive or for other health benefits has been confounded by the low oral bioavailability of its active poly phenolic catechins, particularly epigallocatechin-3-gallate (EGCG), the most active catechin. This review summarized the purported beneficial effects of green tea and EGCG in various animal models of human diseases. Dose-related differences in the effects of EGCG in cancer versus neurodegenerative and cardiovascular diseases, as well as discrepancies between doses used in in vitro studies and achievable plasma understanding of the in vivo effects of green tea catechins in humans, before the use of green tea is widely adopted as health-promoting measure.
Ohmoriet al., (2005) studied to enlighten whether green tea consumption may have these effects in vivo or not, which may be beneficial against atherosclerosis. Green tea has shown to inhibit LDL oxidation, platelet aggregation, and matrix metallo proteinases (MMPs) actions in vitro. They measured serum malondialdehyde-modified LDL (MDA-LDL) concentrations and urine 8-epi-prostaglandin in healthy nonsmokers male. They drank 7 cups of water daily for couple of weeks and drank 7 cups of green tea daily for the next weeks. They concluded that daily consumption of green tea decreased serum MDA-LDL concentrations, but it had no significant effects on platelet aggregation, platelet TX production or plasma MMPs concentrations. Other results suggested that green tea consumption also inhibit LDL oxidation in vivo.
Cheng. (2006) reported that tea is one of the most widely consumed beverages in the world, besides water. It can be categorized into three types, depending on the level of fermentation, i.e., green (unfermented), oolong (partially fermented) and black (fermented) tea. Green tea has been found to be superior to black tea in terms of antioxidant activity owing to the higher content of (−)-epigallocatechingallate. The processes used in the manufacture of black tea are known to decrease levels of the mono-metriccatechins to a much greater extent than the less severe conditions applied to other teas. The cardio-protective effect of flavonoids from green tea can be attributed to not only antioxidant, anti-thrombogenic and anti-inflammatory properties but also improvement of coronary flow velocity reserve. He discussed the effects of green tea on atherosclerosis, coronary heart disease, hypertension, diabetes, metabolic syndrome and obesity, and, finally, its comparison with black tea.
Kuriyamaet al., (2006) performed an experiment on adults without history of stroke, coronary heart disease, or cancer to investigate the associations between green tea consumption and mortality due to cardiovascular diseases, cancer, and all causes. Green tea consumption was inversely associated with mortality due to all causes and due to cardiovascular diseases. The inverse association with all-cause mortality was stronger in women than that of men. In men, the ratio of mortality due to all causes was associated with different green tea consumption. The inverse association with cardiovascular disease mortality was stronger than that with all-cause mortality. Among the types of cardiovascular disease mortality, the strongest inverse association was observed for stroke mortality. In contrast, the hazard ratios of cancer mortality were not significant.
Cabrera et al. (2006) reviewed that tea is the most consumed drink in the world besides water. Green tea is a 'non-fermented tea, and contains more catechins, as compared to black tea or oolong tea. Catechins are in vitro and in vivo strong anti-oxidants, its content of certain minerals and vitamins increases the antioxidant potential. Since ancient times, green tea has been considered by the traditional Chinese medicine as a healthy beverage. Recent human studies suggest that green tea may contribute to reduction in the risk of cardiovascular disease and some forms of cancer, as well as to the promotion of oral health and other physiological functions such as anti-hypertensive effect, obesity control, antibacterial and anti-viral activity, increase in bone mineralization, anti-fibrotic properties, and neuro protective power. Increasing concern in its health benefits has led to the inclusion of green tea in the group of beverages with functional properties.
Koo and Noh, (2007) evidenced from in vitro and in vivo studies that green tea or catechins inhibit the intestinal absorption of dietary lipids. Studies in vitro indicate that green tea catechins, particularly (−)-epigallocatechingallate, interfere with the emulsification, digestion, and solubility of lipids, critical steps involved in the intestinal absorption of dietary fat, cholesterol, and other lipids. Animal and epidemiological studies suggested that green tea catechins may reduce the risk of cardiovascular diseases e.g., coronary heart disease (CHD). The health benefit of green tea had been attributed to its antioxidant and anti-inflammatory properties; however, considerable evidence suggested that green tea and its catechins may reduce the risk of CHD by lowering the plasma levels of cholesterol and triglyceride. Green tea reduced the absorption and tissue accumulation of other lipophilic organic compounds. The available information suggests that green tea or its catechins might be used as safe and effective lipid-lowering therapeutic agents.
Khan and Mukhtar, (2007) reported that although health benefits have been attributed to tea, especially, green tea consumption since many years, scientific investigations of this beverage and its constituents have been underway for less than three decades. People have been consuming brewed tea from the leaves of the Camellia sinensisplant for almost 50 centuries. Currently, tea, in the form of green or black tea, is the most widely consumed beverage in the world. In vitro and animal studies provide strong evidence that polyphenols derived from tea may possess the bioactivity to affect the pathogenesis of several degenerative diseases. Among all tea polyphenols, epigallocatechin-3-gallate of green tea has been shown to be responsible for much of the health promoting ability. Tea and tea preparations have been shown to inhibit tumor formation in a variety of animal models of carcinogenesis.
Wolfram, (2007) suggested that dose-response relationships observed in several epidemiological studies have suggested that pronounced cardiovascular and metabolic health benefits can be obtained by regular consumption of 5-6 or more cups of green tea daily. Intervention studies using similar amounts of green tea, containing 200-300 mg of EGCG, have demonstrated its usefulness for maintaining cardiovascular and metabolic health. Additionally, there are numerous in vivo studies demonstrating that green tea and EGCG exert cardiovascular and metabolic benefits. Therefore, green tea and EGCG can be regarded as food components useful for the maintenance of cardiovascular and metabolic health. To prove the effectiveness for disease prevention or treatment, long-term clinical studies investigating the effects of one precisely-defined green tea product on cardiovascular and metabolic endpoints would benecessary.
Nagao et al, (2007) investigated the effect of green tea catechins in reducing body fat and risk of cardiovascular by in randomly collected Japanese men and women. The individuals were ingested 96-583 mg of green tea catechins daily with normal dietary intake and usual physical activity. The continuous ingestion of green tea high in catechins resulted in body fat, LDL cholesterol and systolic blood pressure, indicating that green tea high in catechins in take results in decrease obesity and cardiovascular risks.
Tinahoneset al. (2008) studied to determine the effect of a green tea extract on vascular function and lipid peroxidation as compared with placebo. The study was carried out with healthy women, none of them were receiving any medical treatment. The consumption of green tea extract was associated with a significant 37.4% reduction in the concentration of oxidized LDL. This study found that consumption of green tea extract by women results in modifications in vascular function and a considerable decrease in serum oxidation.
Chackoet al. (2010) investigatedthe health benefits of green tea for a wide variety of conditions, including cancer, heart disease, and liver disease due to beneficial effects of green tea catechin, particularly (-)-epigallocatechin-3-gallate, content. They related the healthful mechanisms of green tea catechins by evidences from in vitro, animal and human studies. As there were also on using green tea catechins to treat metabolic syndrome, such as obesity, type II diabetes, and cardiovascular risk factors. And they suggested that long term consumption of green tea catechins could be beneficial against high-fat diet-induced obesity and type II diabetes and to reduce the risk of heart disease.
Mineharuet al., (2011) studied to examine the relationship between the consumption of these beverages and risk of mortality from CVD, individuals aged 40-79â€…years free of stroke, coronary heart disease (CHD) and cancer at early stage were prospectively followed. The daily consumption of beverages was assessed by questionnaires. They concluded that consumption of coffee, green tea and oolong tea and caffeine intake was associated with a lower risk of mortality from CVD.
Zhenget al. (2011) identified the effect of green tea and its extract on total cholesterol (TC), LDL cholesterol, and HDL cholesterol. They identified relevant trials of green tea beverages and extracts on lipid profiles in adults. Weighted mean differences were calculated for net changes in lipid concentrations by using fixed-effects or random-effects models. The analysis of studies showed that the consumption of green tea beverages resulted in significant reductions in serum TC and LDL-cholesterol concentrations, but no effect on HDL cholesterol was observed. Analyses showed that these changes were not influenced by the type of intervention, dose of green tea, study duration, individual health status, or quality of the treatment study.