The effect of black tea on risk factors of cardiovascular disease in a normal population. Preventive effects of drinking green tea on cancer and cardiovascular disease: epidemiological evidence for multiple targeting prevention. Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial. Green tea and black tea consumption in relation to colorectal cancer risk: the Singapore Chinese Health Study. Standardized capsule of Camellia sinensis lowers cardiovascular risk factors in a randomized, double-blind, placebo-controlled study. Prospective cohort study of green tea consumption and colorectal cancer risk in women. Green tea consumption and prostate cancer risk in Japanese men: a prospective study. No association between green tea and prostate cancer risk in Japanese men: the Ohsaki Cohort Study.
A prospective randomized controlled clinical trial determined the effect of Mauritian black tea consumption on fasting blood plasma levels of glucose, lipid profiles and antioxidant status in a normal population.
                The study group (71%) consumed 3 x 200 ml of black tea infusate/day for 12 weeks without additives followed by a 3 week wash-out. The control group (29%) consumed equivalent volume of hot water for same intervention period.
                The tea used had high levels of gallic acid derivatives (50 ± 0.4 mg/L), flavan-3-ols (42 ± 2 mg/L), flavonols (32 ± 1 mg/L) and theaflavins (90 ± 1 mg/L). Daily 9 g supplementation of black tea infusate induced, in a normal population, a highly significant decrease of fasting serum glucose (18.4%; p<0.001) and triglyceride levels (35.8%; p<0.01), a significant decrease in LDL/HDL plasma cholesterol ratio (16.6%; p<0.05) and a non significant increase in HDL plasma cholesterol levels (20.3%), while a highly significant rise in plasma antioxidant propensity (FRAP: 418%; p<0.001) was noted .
                Black tea consumed within a normal diet contributes to a decrease of independent cardiovascular risk factors and improves the overall antioxidant status in humans.
                Copyright © 2011 Elsevier Inc. All rights reserved. The significance of drinking green tea in prevention of two of the main lifestyle-related diseases, cancer and cardiovascular disease, was demonstrated in terms of a prospective cohort study on a total of 8,552 general residents in Saitama Prefecture, Japan. On the basis of the follow-up study, we revealed decreased relative risk of cancer incidence for those consuming over 10 cups a day, compared with those consuming below 3 cups: 0.54 (95% confidence interval, 0.22-1.34) for men, 0.57 (0.34-0.98) for women, and 0.59 (0.35-0.98) for both sexes. Furthermore, a significant delay in cancer onset was associated with increased consumption of green tea. Next, decreased relative risk of death from cardiovascular disease was 0.58 (0.34-0.99) for men, 0.82 (0.49-1.38) for women, and 0.72 (0.60-1.04) for members of both sexes consuming over 10 cups a day. Finally, we evaluated the life-prolonging effects of drinking green tea on cumulative survival, using the life table. Tea consumption has been associated with decreased cardiovascular risk, but potential mechanisms of benefit are ill-defined. While epidemiologic studies suggest that drinking multiple cups of tea per day lowers low-density lipoprotein cholesterol (LDL-C), previous trials of tea drinking and administration of green tea extract have failed to show any impact on lipids and lipoproteins in humans. Our objective was to study the impact of a theaflavin-enriched green tea extract on the lipids and lipoproteins of subjects with mild to moderate hypercholesterolemia.
                Double-blind, randomized, placebo-controlled, parallel-group trial set in outpatient clinics in 6 urban hospitals in China. A total of 240 men and women 18 years or older on a low-fat diet with mild to moderate hypercholesterolemia were randomly assigned to receive a daily capsule containing theaflavin-enriched green tea extract (375 mg) or placebo for 12 weeks. Main outcome measures were mean percentage changes in total cholesterol, LDL-C, high-density lipoprotein cholesterol (HDL-C), and triglyceride levels compared with baseline.
                After 12 weeks, the mean +/- SEM changes from baseline in total cholesterol, LDL-C, HDL-C, and triglyceride levels were -11.3% +/- 0.9% (P =.01), -16.4% +/- 1.1% (P =.01), 2.3% +/- 2.1% (P =.27), and 2.6% +/- 3.5% (P =.47), respectively, in the tea extract group. The mean levels of total cholesterol, LDL-C, HDL-C, and triglycerides did not change significantly in the placebo group. No significant adverse events were observed.
                The theaflavin-enriched green tea extract we studied is an effective adjunct to a low-saturated-fat diet to reduce LDL-C in hypercholesterolemic adults and is well tolerated. The relationships between green tea and black tea consumption and colorectal cancer risk were examined within the Singapore Chinese Health Study, a prospective cohort study of diet and cancer involving >60,000 men and women. Intake of green tea and black tea was assessed through in-person interviews. Incident cancer cases and deaths among cohort members were identified through record linkage of the cohort database with respective databases from the nationwide Singapore Cancer Registry and the Singapore Registry of Births and Deaths. The proportional hazard regression method was used to examine the associations between intake of green and black tea separately and colorectal cancer risk with adjustment for potential confounders. After an average of 8.9 years of follow-up, 845 colorectal cancer cases were identified. Subjects who drank green tea exhibited a statistically non-significant increase in risk [relative risk (RR) = 1.12, 95% confidence interval (CI) = 0.97-1.29] relative to non-drinkers of green tea. This risk increase was mainly confined to men (RR = 1.31, 95% CI = 1.08-1.58); the comparable RR in women was 0.89 (95% CI = 0.71-1.12). In men, the green tea-colorectal cancer association was noted mainly in those with advanced disease (Duke C or D) (RR = 1.53, 95% CI = 1.19-1.97), and the association was dose dependent (P for trend = 0.0002). This latter association was especially strong within the colon subsite (RR = 1.75, 95% CI = 1.24-2.46; P for trend < 0.0001). Irrespective of gender, intake of black tea was not associated with risk of colorectal cancer (RR = 0.92, 95% CI = 0.79-1.07) in this Asian population. Previous studies examining the effect of tea drinking on cardiovascular health have produced mixed results due to their observational nature and qualitatively and quantitatively imprecise definitions of active tea components. The objective of this study was to determine if a standardized and defined decaffeinated green tea (Camellia sinensis) product lowers blood pressure, serum lipids, oxidative stress, and markers of chronic inflammation.
                A randomized, double-blind, placebo-controlled, parallel study on 111 healthy adult volunteers 21-70 y old was performed. We administered a standardized capsule of Camellia sinensis compounds (CSC) twice a day. Before and after 3 wk, blood pressure, serum lipids, serum amyloid-alpha (a marker of chronic inflammation), and serum malondialdehyde (a marker of oxidative stress) were measured.
                After 3 wk, CSC lowered systolic and diastolic blood pressures by 5 and 4 mmHg, respectively. After 3 mo, systolic blood pressure remained significantly lower. CSC lowered serum amyloid-alpha by 42% and lowered malondialdehyde by 11.9%. In men, there were 10- and 9-mg/dL reductions in total and low-density lipoprotein (LDL) cholesterol, respectively. In all subjects with a baseline LDL cholesterol level >99 mg/dL, there was 9 mg/dL lowering of total and LDL cholesterol. Adverse effects were mild and few and not different from placebo.
                CSC was effective for decreasing, in as quickly as 3 wk, blood pressure, LDL cholesterol, oxidative stress, and a marker of chronic inflammation, all independent cardiovascular risk factors. Tea and its constituents have shown anticarcinogenic activities in in vitro and animal studies. Epidemiologic studies, however, have been inconsistent. We prospectively evaluated the association between green tea consumption and colorectal cancer (CRC) risk in a cohort of 69,710 Chinese women aged 40 to 70 years. Information on tea consumption was assessed through in-person interviews at baseline and reassessed 2 to 3 years later in a follow-up survey. During 6 years of follow-up, 256 incident cases of CRC were identified. The multivariate relative risk of CRC was 0.63 (95% confidence interval, 0.45-0.88) for women who reported drinking green tea regularly at baseline compared with nonregular tea drinkers. A significant dose-response relationship was found for both the amount of tea consumed (Ptrend = 0.01) and duration in years of lifetime tea consumption (Ptrend = 0.006). The reduction in risk was most evident among those who consistently reported to drink tea regularly at both the baseline and follow-up surveys (relative risk, 0.43; 95% confidence interval, 0.24-0.77). The inverse association with regular tea drinking was observed for both colon and rectal cancers. This study suggests that regular consumption of green tea may reduce CRC risk in women. The incidence of prostate cancer is much lower in Asian than Western populations. Given that environmental factors such as dietary habits may play a major role in the causation of prostate cancer and the high consumption of green tea in Asian populations, this low incidence may be partly due to the effects of green tea. The JPHC Study (Japan Public Health Center-based Prospective Study) was established in 1990 for cohort I and in 1993 for cohort II. The subjects were 49,920 men aged 40-69 years who completed a questionnaire that included their green tea consumption habit at baseline and were followed until the end of 2004. During this time, 404 men were newly diagnosed with prostate cancer, of whom 114 had advanced cases, 271 were localized, and 19 were of an undetermined stage. Green tea was not associated with localized prostate cancer. However, consumption was associated with a dose-dependent decrease in the risk of advanced prostate cancer. The multivariate relative risk was 0.52 (95% confidence interval: 0.28, 0.96) for men drinking 5 or more cups/day compared with less than 1 cup/day (p(trend) = 0.01). Green tea may be associated with a decreased risk of advanced prostate cancer. In a prospective study of 19,561 Japanese men, green-tea intake was not associated with a lower risk of prostate cancer (110 cases), the multivariate hazard ratio for men drinking > or =5 cups compared with <1 cup per day being 0.85 (95% confidence interval 0.50-1.43, trend P = 0.81).
There are very few long-term studies to date examining green or black tea for the primary prevention of CVD. The limited evidence suggests that tea has favourable effects on CVD risk factors, but due to the small number of trials contributing to each analysis the results should be treated with some caution and further high quality trials with longer-term follow-up are needed to confirm this.