Green Tea Drinking Research Articles

Catechin stability of EGC- and EGCG-enriched tea drinks produced by a two-step extraction procedure

Catechin content of green tea drinks commercially available is reported to be very low in comparison with tea traditionally prepared, due to catechins conversion to their corresponding epimers during production. The purpose of this present study was to produce catechin-enriched tea drinks according to a two-step brewing procedure and to verify the catechin stability of those enriched drinks during storage. Those results confirmed that it is possible to produce EGC- and EGCG-enriched tea drinks regardless of the green tea used. Good extraction efficiencies were reached for the first and second extraction steps with catechin extraction yields ranging from 63.6% to 84.8%. Furthermore, it appeared that the catechin content in the two enriched tea drinks demonstrated a great stability since no significant degradation occurred within 8 weeks of storage. This simple two-step extraction procedure could be considered as an interesting way to produce enriched green tea drinks with more potent and stable bioactive catechins.

Element Composition of Tea Leaves and Tea Infusions and Its Impact on Health

Tea infusion is the most frequently consumed beverage worldwide next to water, with about 20 billion cups consumed daily. In Taiwan, daily consumption averages 2.5 cups of tea infusion per person. Many studies have concluded that tea has numerous beneficial effects on health. However, some undesirable trace elements, such as arsenic, chromium, cadmium, lead, etc., are a concern. This study has three aims: (1) to measure the concentrations of arsenic and heavy metal elements, such as chromium, cadmium, and lead, as well as the essential trace elements contained in dried tea leaves of the common brands in Taiwan; (2) to determine the percentage released and concentration of each of these elements after infusion of these tea leaves with boiling water; (3) to assess the carcinogenic risk from daily tea consumption, to provide reference values for the general public. This study showed the total content of arsenic and heavy metals in green tea, oolong tea, and black tea produced in Taiwan was 0.11, 5.61, and 10.11 microg/g, respectively, indicating that the level of arsenic and heavy metal contamination of tea leaves was lower in Taiwan than other regions of the world. The hazard index (HI) of daily tea drinking of green tea, oolong tea, and black tea was low and within the bounds of safety (<1). Tea is an indispensable part of everyday life for many people in Taiwan, studies should continue to ensure that public health is maintained.

Green tea and coffee intake and risk of pancreatic cancer in a large-scale, population-based cohort study in Japan (JPHC study)

Pancreatic cancer is one of the most aggressive and treatment-refractory malignancies in humans. The most effective means of reducing pancreatic cancer mortality may be primary prevention. Although laboratory studies have demonstrated that green tea possesses anticancer activities, results from epidemiological studies have failed to show a consistent cancer-preventive effect. In addition, there is a lingering concern that coffee mighty increase the risk of pancreatic cancer although the most recent epidemiological studies showed no overall association between coffee and risk. Here, we examined the association between the drinking of green tea or coffee and the risk of pancreatic cancer in a large population-based cohort study in Japan (JPHC study). In total, 102 137 participants were followed for an average of 11 years through to the end of 2003. A total of 233 incident cases of pancreatic cancer were identified among 1 116 945 person-years of follow-up. Overall, the risk of pancreatic cancer was not associated with either green tea or coffee intake in our population, although a reduced risk was apparent among men who drank at least three cups of coffee per day compared with those who did not drink any or only rarely drank coffee. In conclusion, our findings support the idea that green tea or coffee consumption does not have a substantial impact on pancreatic cancer risk in general.

Diet and lifestyle associated with increased bone mineral density: cross-sectional study of Japanese elderly women at an osteoporosis outpatient clinic

BackgroundSeveral studies have already demonstrated that lifestyle characteristics, such as physical activity, smoking, and alcohol intake, are associated with bone mineral density (BMD). Coffee intake was shown to be negatively associated with BMD, whereas tea drinking was reported to be associated with increased BMD. A review of the literature, however, revealed that few studies have described the association between BMD and lifestyle, including characteristic Japanese foods such as fish, natto, and Japanese green tea. The aim of this study was to identify lifestyle factors associated with BMD. MethodsA total of 632 women age ≥60 years were enrolled in this study. Subjects were interviewed about their lifestyle by means of a questionnaire regarding the consumption pattern of dietary items. BMD was measured at the lumbar spine by dual energy X-ray absorptiometry. ResultsThe BMD was higher in subjects with the habits of alcohol drinking, green tea drinking, and physical activity and lower in those with the habits of smoking and cheese consumption. Multiple regression analysis showed that factors associated with BMD were smoking, alcohol consumption, green tea drinking, and physical activity after adjusting for age and body mass index (BMI). ConclusionsIn this cross-sectional study at an osteoporosis outpatient clinic, patients with the habits of alcohol drinking, green tea drinking, and physical activity had significantly higher BMD, and those who smoked had significantly lower BMD than patients without each habit after adjusting for age, BMI, and other variables regarding lifestyle.

Effects of Soil Selenium Supplementation Level on Selenium Contents of Green Tea Leaves and Milk Vetch

This study was conducted to investigate the effects of soil selenium (Se) supplementation level on Se contents of green tea and milk vetch. Four different concentrations of sodium selenite (Na₂SeO₃) solutions (0.0, 3.3, 33.0 and 165.0 ㎍/mL) were prepared and one liter of each solution was well mixed with 10 ㎏ of compost (cowpea soil) to give four different levels of Se-containing soil: T₁, 0; T₂, 33; T₃, 330; T₄, and 1,650 ㎍/100 g soil. Green tea plants and milk vetch were individually cultivated in those soils for 60 days. Se contents of freeze-dried green tea leaves were 6.87, 10.40, 12.04, and 20.19 ㎍/g, respectively; all of which were significantly different (p＜0.05) from the others except for T₂ and T₃. The results showed that Se-contents of green tea leaves were increased 1.5～2.9 times as the Se level in the soil increased. Regression equation between Se contents in green tea (Y) and soil Se supplementation level (X) was: Y=0.007X＋8.857. However, Se contents in the milk vetch were increased significantly (p＜0.05) more with the same treatments T₃ (74 ㎍/g) and T₄ (187 ㎍/g) in comparison to those at T₁ (5.0 ㎍/g) and T₂ (12.0 ㎍/g). The increases ranged from approximately between 2.4 to 37.4 times that of the control group. Regression equation between Se contents in milk vetch (Y) and soil Se supplementation level (X) was: Y=0.1063X＋15.989. The large difference of Se contents between green tea leaves and milk vetch would be attributed by the difference of protein contents between the 30% or higher protein-content of legumes and 15～20% protein of shrubs. The present study clearly indicates that green tea leaves and milk vetch can be enriched in selenium by supplementing the soil with Se. Therefore, Se-enriched green tea or milk vetch powder could be utilized as functional foods in Se-fortified green tea drinks or salads, or as food additives to enhance the daily intake of Se.

Diet habits, alcohol drinking, tobacco smoking, green tea drinking, and the risk of esophageal squamous cell carcinoma in the Chinese population

This study aims to investigate the risk of esophageal squamous cell carcinoma in relation to exogenous factors in a rural area of China with a high incidence of esophageal squamous cell carcinoma. A population-based case-control study was conducted in Yangzhong County, Jiangsu Province, China, with 355 histologically confirmed esophageal squamous cell carcinoma cases recruited between 1 January 2004 and 28 February 2006 and 408 controls matched by sex and age, randomly selected from the local population. Stratified logistic regression analysis by sex revealed that hot-temperature food items, pork braised in brown sauce and old stocked rice intake could increase the risk of esophageal squamous cell carcinoma with odds ratio of 2.127 (95% confidence interval: 1.394-3.245), 2.059 (95% confidence interval: 1.417-2.993) and 9.059 (95% confidence interval: 5.930-13.840), respectively, in men and 3.048 (95% confidence interval: 1.733-5.364), 1.914 (95% confidence interval: 1.159-3.162) and 14.532 (95% confidence interval: 7.816-27.019), respectively, in women, whereas diet high in salt and chili, tobacco smoking and alcohol drinking only showed possible risk effects in men with odds ratio 2.338 (95% confidence interval: 1.568-3.485), 3.378 (95% confidence interval: 2.117-5.389), 1.976 (95% confidence interval: 1.337-2.921) and 2.197 (95% confidence interval: 1.510-3.195), respectively. Green tea drinking showed a protective effect in women (odds ratio=0.257; 95% confidence interval: 0.070-0.941). Findings from this study provided evidence that dietary habits, tobacco-smoking and alcohol drinking contribute to the etiology of esophageal squamous cell carcinoma. A healthy dietary habit, with smoking cessation and alcohol controlling is of a great importance in the prevention of esophageal cancer.

The anti-fibrotic effect of green tea with a high catechin content in the galactosamine-injured rat liver

Previously, we reported that the oral administration of green tea rich in catechins restored levels of several biomarkers increasing in galactosamine-treated rats to nearly control values. These biomarkers included serum transaminase activities, serum concentrations of tumor necrosis factor-alpha and interleukin 1-beta, and the hepatic mRNA expression of these inflammatory cytokines. In the present study, we examined possible anti-fibrotic effects of green tea in galactosamine-induced hepatitis. The results of the reverse transcription and polymerase chain reaction indicated that the increase in gene expression of the alpha1 chain of collagen type 1 and transforming growth factor beta-1 in the injured liver 24 h post-injection of galactosamine was suppressed by the administration of green tea. Masson's trichrome staining demonstrated that the extent of fibrogenesis after 14 days was greater in the galactosamine-injured livers not treated with green tea than the treated ones. These results suggest that the drinking of green tea with a high catechin content may help to prevent and/or attenuate the development of fibrosis in hepatitis.

Green tea and the prevention of breast cancer: a case-control study in Southeast China

Breast cancer is the most common malignancy in women worldwide. Tea has anticarcinogenic effects against breast cancer in experimental studies. However, epidemiologic evidence that tea protects against breast cancer has been inconsistent. A case-control study was conducted in Southeast China between 2004 and 2005. The incidence cases were 1009 female patients aged 20-87 years with histologically confirmed breast cancer. The 1009 age-matched controls were healthy women randomly recruited from breast disease clinics. Information on duration, frequency, quantity, preparation, type of tea consumption, diet and lifestyle were collected by face-to-face interview using a validated and reliable questionnaire. Conditional logistic regression analyses were used to estimate odds ratios (ORs) and associated 95% confidence intervals. Compared with non-tea drinkers, green tea drinkers tended to reside in urban, have better education and have higher consumption of coffee, alcohol, soy, vegetables and fruits. After adjusting established and potential confounders, green tea consumption was associated with a reduced risk of breast cancer. The ORs were 0.87 (0.73-1.04) in women consuming 1-249 g of dried green tea leaves per annum, 0.68 (0.54-0.86) for 250-499 g per annum, 0.59 (0.45-0.77) for 500-749 g per annum and 0.61 (0.48-0.78) for >or=750 g per annum, with a statistically significant test for trend (P < 0.001). Similar dose-response relationships were observed for duration of drinking green tea, number of cups consumed and new batches prepared per day. We conclude that regular consumption of green tea can protect against breast cancer. More research to closely examine the relationship between tea consumption and breast cancer risk is warranted.

The effect of green tea in oxidative stress

Green tea, an infusion prepared with the leaves of Camellia sinensis is particularly rich in flavonoids, which are strong antioxidants. Tea drinking, by providing antioxidants, may become valuable in several oxidative stress conditions. Our aim was to evaluate the effect of green tea drinking on some factors reflecting the development of oxidative stress in plasma and in erythrocytes. The study was performed in 34 Portuguese subjects. We evaluated the total antioxidant status (TAS), the lipid peroxidation products-malonyldialdehyde (MDA) and malonyldialdehyde+4-hydroxy-2(E)-nonenal (MDA+4-HNE)-and the oxidative changes in erythrocyte membrane, namely membrane bound haemoglobin (MBH) and the band 3 profile. Analytical evaluations were performed after 3 weeks drinking 1l of water daily, and after 4 weeks drinking 1l of green tea daily. Tea was prepared daily at the same conditions of temperature, time of infusion and concentration. After green tea drinking, we found a significant reduction in serum levels of MDA and MDA+4-HNE and in the oxidative stress within the erythrocyte, as suggested by a significantly lower value of MBH and by changes in band 3 profile towards a normal mean profile, namely an increase in the band 3 monomer. A rise in the antioxidant capacity was also observed. Our data suggest for green tea drinking a beneficial effect, by reducing the development or the enhancement of oxidative stress and, therefore, protecting the individual for oxidative stress diseases. Moreover, we propose further studies about the value of band 3 profile and of MBH in providing a cumulative measurement of the effect of green tea drinking upon the oxidative stress in cells. Moreover, further studies are also needed, to clarify the effect of green tea consumption, the value of regular green tea consumption and the way it should be prepared to reach a healthy effect.

Habitual green tea consumption and risk of an aneurysmal rupture subarachnoid hemorrhage: A case–control study in Nagoya, Japan

Green tea, a popular beverage in Japan, contains many polyphenolic antioxidants, which might prevent cardiovascular disease. This study is designed to determine whether the consumption of green tea is associated with a reduced risk for subarachnoid hemorrhage (SAH) using a case-control study. Incident SAH cases (n=201) were identified and individually matched by age (+/-2 years) and gender to hospital (n=201) and community controls (n=201) from April 1992 to March 1997. Habitual regular tea consumption was assessed with a structured questionnaire. Conditional logistic regression models were used to compute odds ratios adjusted for smoking, history of hypertension, and educational levels. The proportion of the consumption of one time or more of tea per day was higher in controls (70.9%) than in SAH patients (60.3%). Multivariate analyses showed that green tea consumption was inversely associated with SAH risk. Subjects consuming <1, and >or=1 time per day had adjusted ORs of 0.74 (CI: 0.34-1.58), and 0.56 (CI: 0.32-0.98) in comparison with non daily green tea drinkers, respectively (p-trend <0.001). In a case-control study in Japan, we found that habitual green tea consumption may be strongly associated with a reduced risk for SAH. Our findings will be useful in targeting individuals and populations for the primary prevention of SAH.

A Frequent Drinking of Green Tea Lowers the Levels of Endogenous Oxidative Stress in Small Intestines, Erythrocytes and Kidneys in Rats

Endogenous antioxidative potential was examined in rats given green tea as daily drinking water for 4 weeks. Rats ingested 196 μmol/kg body weight/day of catechins (sum total of 8 kinds of catechins), and plasma levels were around 0.24 μM. The green tea also contained 2.1 mM ascorbic acid, but the plasma level was similar to that in control rats drinking water, about 30 μM. The tea-drinking rats had significantly lower levels of lipid peroxidation in the small intestines and kidneys, 30% and 40% lower, respectively, than the controls, and their erythrocytes showed significant resistance to aqueous peroxyl radicals generated from azo initiator. Then, the effects of 8 catechins were examined on the antioxidative potency of ascorbic acid in in vitro. Catechins suppressed the oxidation of deoxyguanosine after the immediate exhaustion of ascorbic acid. Thus, frequent daily drinking of green tea improved the antioxidative potential of ascorbic acid.

Smoking, Alcohol Drinking, Green Tea Consumption and the Risk of Esophageal Cancer in Japanese Men

BACKGROUNDAlthough smoking and alcohol drinking are established risk factors of esophageal cancer, their public health impact is unclear. Furthermore, the effect of green tea is controversial.METHODSThe present study was based on a pooled analysis of two prospective cohort studies. A self-administered questionnaire about health habits was distributed to 9,008 men in Cohort 1 and 17,715 men in Cohort 2, aged 40 years or older, with no previous history of cancer. We identified 38 and 40 patient cases with esophageal cancer among the subjects in Cohort 1 (9.0 years of follow-up) and Cohort 2 (7.6 years of follow-up), respectively. Cox proportional hazards regression was used to estimate hazard ratios (HRs) of the risk of esophageal cancer incidence.RESULTSCigarette smoking, alcohol drinking and green tea consumption were significantly associated with an increased risk of esophageal cancer. Compared with men who had never smoked, never drunk alcohol or green tea, the pooled multivariate HRs (95% confidence intervals) were 5.09 (1.80-14.40) (p for trend <0.0001), 2.73 (1.55-4.81) (p for trend=0.0002), or 1.67 (0.89-3.16) (P for trend=0.04) for men who were currently smoking ≥20 cigarettes/day, drinking alcohol daily, or drinking ≥5 cups green tea/day, respectively. The population attributable fractions of esophageal cancer incidence that was attributable to smoking, alcohol drinking and green tea consumption were 72.0%, 48.6%, and 22.1%, respectively.CONCLUSIONSAmong the variables studied, smoking has the largest public health impact on esophageal cancer incidence in Japanese men, followed by alcohol drinking and green tea drinking.

Favorable Effects of Tea on Reducing the Cognitive Deficits and Brain Morphological Changes in Senescence-Accelerated Mice

The present study was carried out to explore the effects of oolong and green teas on improving the memory deficits and brain pathological changes in senescence accelerated-prone mice P8 (SAMP8). Six-month-old mice were supplied with oolong tea, green tea or water as the sole drinking fluid for 16 wk. The memory ability of mice was evaluated by passive and active avoidance tests, while the extent of the brain degeneration was measured by the spongiosis grades and the lipofuscin percentage in the hippocampus. The total grading score and serum biochemical levels were also measured. The results indicated that the mice supplemented with the oolong and green tea drinks reversed the cognitive impairment, lessened the spongy degeneration and lipofuscin, and increased the serum Trolox equivalent antioxidant capacity more than the control group. The total grading score of the oolong tea group was lower than that of the control group in male mice, whereas it did not differ among female groups. No differentiations in the concentrations of total cholesterol. triglyceride, glucose, iron or hemoglobin were observed among three drink groups. In conclusion, oolong and green teas could reduce the deteriorations of cognitive ability, brain degenerative changes and aging process in SAMP8, probably through the potent antioxidative activity of the tea.

Rapid Determination of Eight Catechins in Bottled Green Tea Drinks using Isocratic Elution Method/RP-HPLC-UV

An accurate, simple and rapid isocratic elution method for the simulutaneous determination of eight catechins in bottled green tea drinks using reversed-phase (RP) high performance liquid chromatography (HPLC) with ultraviolet detecter (UV) and short column (100 mm×4.6 mm i. d., particle diameter 3 μm) has been studied. As a result, good linearity of the calibration curve were obtained in the concentration range from 1 mg l-1 to 100 mg l-1 (|r| =0.9998-0.9974) . The detection limits based on S/N=3 were 0.62 mg l-1 for (-) -gallocatechin (GC), 0.78 mg l-1 for (-) -epigallocatechin (EGC), 0.59 mg l-1for (+) -catechin (C), 0.38 mg l-1 for 7- (β-hydroxyethyl) theophylline, 0.42 mg l-1 for (-) -epigallocatechin gallate (EGCg), 0.57 mg l-1 for (-) -epicatechin (EC), 0.48 mg l-1 for (-) -gallocatechin gallate (GCg), 0.40 mg l-1 for (-) -epicatechin gallate (ECg), and 0.43 mg l-1 for (-) -catechin gallate (Cg) in 5 μl injection. The eight catechins and 7- (β-hydroxyethyl) theophylline were separated by an isocratic elution method within 30 min. This Isocratic elution method could be successfully applied to the rapid determination of eight catechins in bottled green tea drinks.

Protective effect of green tea on erythrocyte membrane of different age rats intoxicated with ethanol

It is known that aging is characterized by changes in cell metabolism resulting in modification of the structure and function of cell membrane components which is mainly the consequence of reactive oxygen species action. These disturbances are also enhanced by different xenobiotics, e.g. ethanol. Therefore, the aim of this paper is to examine green tea influence on total antioxidant status (TAS) and on composition and electric charge of erythrocyte membrane phospholipids in ethanol intoxicated rats of various ages. Antioxidant abilities of erythrocytes were estimated by measuring TAS. Qualitative and quantitative composition of phospholipids in the membrane was determined by HPLC, while the extent of erythrocytes lipid peroxidation was estimated by HPLC measurement of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) levels. Electrophoresis was used to determine the surface charge density of the rat erythrocyte membrane. It was shown that the process of aging was accompanied by a decrease in TAS and in the total amount of phospholipids as well as by enhancement of lipid peroxidation and increase in surface charge density of erythrocyte membrane. Ethanol administration caused, in term, decrease in TAS and increase in the level of all phospholipids and lipid peroxidation products. Ethanol as well significantly enhanced changes in surface charge density of erythrocyte membrane. The ingestion of green tea partially prevented decrease in erythrocyte antioxidant abilities observed during aging and ethanol intoxication. Moreover, long-term drinking of green tea protects the structure of the erythrocytes membrane disturbed during aging process and/or chronic ethanol intoxication.

The Wonder of Plants

Epidemiological studies suggest that higher tea consumption was associated with lower risk of depressive symptoms, but this has not been found consistently. Moreover, the effect of different types of tea on depressive symptoms needs to be further explored. This study aimed to examine the association between tea consumption and depressive symptoms in Chinese elderly.We analyzed the baseline data from Zhejiang Major Public Health Surveillance Program including 9371 participants. Depressive symptoms was assessed through the application of Patient Health Questionnaire-9 scale (PHQ-9). Logistic regression models, controlled for an extensive range of potential confounders, were generated to evaluate the association between tea consumption and risk of depressive symptoms.The black tea drinkers had a significantly decreased risk of depressive symptoms (p<0.01), whereas no association was found in green tea drinkers. Compared with non-drinkers, the adjusted ORs (95% CIs) were 0.48 (0.23, 0.99) and 0.35 (0.17, 0.72) for participants consuming <3 cups and ≥3 cups of black tea per day, respectively (P for trend: <0.01). A linear association between concentration of black tea and depressive symptoms was also confirmed in our study.Cross-sectional data could not make a causation conclusion, and the observed association in our study could not be ascribed to any specific component in tea.Our results indicated that higher black tea consumption was associated with a lower prevalence of depressive symptoms in the elderly.

Green tea drinking and multigenetic index on the risk of stomach cancer in a Chinese population

The purpose of our study was to examine the roles of green tea drinking, other risk and protective factors, and polymorphism of susceptibility genes such as GSTM1, GSTT1, GSTP1, and p53 codon 72 and their possible joint effects on the risk of stomach cancer. A population-based case-control study was conducted in Taixing, China, including 206 newly diagnosed cases with stomach cancer and 415 healthy control subjects. Epidemiological data were collected by in-person interviews using a standard questionnaire. Polymorphisms of susceptibility genes were assayed by PCR-RFLP techniques. A multigenetic index was created by summing up the number of risk genotypes. The data were analyzed using the logistic regression model. A reverse association between green tea drinking and risk of stomach cancer was observed with an adjusted odds ratio (OR) of 0.59 (95% confidence interval [CI] = 0.34-1.01). Dose-response relationship was shown (p-trend < 0.05). A higher score on the multigenetic index was associated with increased risk of stomach cancer with an adjusted OR of 2.21 (95% CI = 1.02-4.79) for those with at least 3 risk genotypes compared to those with <2 risk genotypes. Green tea drinking was suggested to have more than multiplicative interactions with alcohol consumption with an adjusted OR for interaction of 4.57 (95% CI = 1.62-12.89), and with higher multigenetic index with adjusted OR for interaction of 2.31 (95% CI = 0.88-6.03). The protective effect of green tea drinking was observed on the risk of stomach cancer and the possible effect modification by susceptibility genes was suggested.

The Antifolate Activity of Tea Catechins

A naturally occurring gallated polyphenol isolated from green tea leaves, (-)-epigallocatechin gallate (EGCG), has been shown to be an inhibitor of dihydrofolate reductase (DHFR) activity in vitro at concentrations found in the serum and tissues of green tea drinkers (0.1-1.0 micromol/L). These data provide the first evidence that the prophylactic effect of green tea drinking on certain forms of cancer, suggested by epidemiologic studies, is due to the inhibition of DHFR by EGCG and could also explain why tea extracts have been traditionally used in "alternative medicine" as anticarcinogenic/antibiotic agents or in the treatment of conditions such as psoriasis. EGCG exhibited kinetics characteristic of a slow, tight-binding inhibitor of 7,8-dihydrofolate reduction with bovine liver DHFR (K(I) = 0.109 micromol/L), but of a classic, reversible, competitive inhibitor with chicken liver DHFR (K(I) = 10.3 micromol/L). Structural modeling showed that EGCG can bind to human DHFR at the same site and in a similar orientation to that observed for some structurally characterized DHFR inhibitor complexes. The responses of lymphoma cells to EGCG and known antifolates were similar, that is, a dose-dependent inhibition of cell growth (IC50 = 20 micromol/L for EGCG), G0-G1 phase arrest of the cell cycle, and induction of apoptosis. Folate depletion increased the sensitivity of these cell lines to antifolates and EGCG. These effects were attenuated by growing the cells in a medium containing hypoxanthine-thymidine, consistent with DHFR being the site of action for EGCG.

Tea and circulating estrogen levels in postmenopausal Chinese women in Singapore

The role of tea in the etiology of breast cancer is controversial. We recently provided the first set of human evidence that breast cancer risk is significantly inversely associated with tea intake, largely confined to intake of green tea. Since black tea and green tea possess comparable levels of the total tea polyphenols that possess antioxidative activities, reasons for the paradoxical effects of green tea and black tea on breast cancer protection are not apparent. Some limited evidence suggests that green tea may have downregulatory effects on circulating sex-steroid hormones, whereas black tea may have upregulatory effects. We therefore, investigated the relationship between tea intake, and plasma estrogen and androstenedione levels in a cross-sectional study of healthy postmenopausal Chinese women in Singapore. In this group of 130 women, 84 were non or irregular (less than once a week) tea drinkers, 27 were regular (weekly/daily) green tea drinkers and 19 were regular (weekly/daily) black tea drinkers. Relative to plasma estrone levels in non- or irregular tea drinkers (29.5 pg/ml) the levels were 13% lower in regular green tea drinkers (25.8 pg/ml) and 19% higher in regular black tea drinkers (35.0 pg/ml). These differences in estrone levels were statistically significant (P = 0.03) inspite of adjusting for age, body mass index, intake of soy, and other covariates. A similar pattern of differences between tea intake, and plasma levels of estradiol (P = 0.08) and androstenedione (P = 0.14) were found. In addition, the tea-estrogen associations were observed irrespective of the genotype of catechol-O-methyltransferase (COMT), a major enzyme that aids in the excretion of tea polyphenols in humans. Larger studies are needed to confirm results from this cross-sectional study and to better understand the potentially differing effect of black and green tea on circulating estrogen levels and ultimately on the risk of breast cancer.

Green tea with a high catechin content suppresses inflammatory cytokine expression in the galactosamine-injured rat liver

Galactosamine is known to induce hepatic injury in rats and the galactosamine-induced hepatitis is believed to be similar to viral hepatitis both morphologically and functionally. In the present study, we examined how drinking green tea affects the gene expression of inflammatory cytokines which may be up-regulated in galactosamine-induced hepatitis. As has been reported, galactosamine caused hepatic injury in rats as evidenced by an increase in serum transaminase activities and histological observations of the liver. The results of the reverse transcription and polymerase chain reaction indicated an increased gene expression of inflammatory cytokines, tumor necrosis factor-alpha and interleukin-1beta, in the injured liver and the enzyme linked immunoassay showed an increase in the serum levels of these cytokines. Oral administration of green tea rich in catechins (Healthya green tea) restored these biomarkers in the galacotsamine-treated rats to near the control levels. These results suggest that the drinking of green tea with a high catechin content may help to prevent and/or attenuate the development of a certain type of hepatitis.