Black tea consumption dose-dependently improves flow-mediated dilation in healthy males

Department of Internal Medicine and Public Health, University of L'Aquila, L'Aquila, Italy.
Journal of Hypertension (Impact Factor: 4.72). 04/2009; 27(4):774-81. DOI: 10.1097/HJH.0b013e328326066c
Source: PubMed


Flavonoids may protect against cardiovascular disease. Tea is a major source of dietary flavonoids. Studies indicate black tea improves endothelial function but data on arterial haemodynamics, blood pressure (BP) and insulin resistance are equivocal. Inconsistency may be due to flaws in study design or flavonoid doses tested. Further, no study has evaluated the dose-response curve. Our study aimed to test the effects of various doses of black tea on vascular function, BP and insulin resistance.
According to a randomized, double-blind, controlled, cross-over design, 19 healthy men were assigned to receive either five treatments with a twice daily intake of black tea (0, 100, 200, 400 and 800 mg tea flavonoids/day) in five periods lasting 1 week each.
Black tea dose dependently increased flow-mediated dilation (FMD) from 7.8% (control) to 9.0, 9.1, 9.6 and 10.3% after the different flavonoid doses, respectively (P = 0.0001). Already 100 mg/day (less than 1 cup of tea) increased FMD compared with control (P = 0.0113). FMD improvement after 800 mg/day was significant compared with control (P < 0.0001) but also to 100 mg/day (P = 0.0121) and 200 mg/day (P = 0.0275). Black tea intake decreased office systolic (-2.6 mmHg, P = 0.0007) and diastolic (-2.2 mmHg, P = 0.006) BP as well as stiffness index (P = 0.0159) without changes in other parameters studied.
Our study is the first showing black tea ingestion dose dependently improved FMD and decreased peripheral arterial stiffness in healthy volunteers. Our data suggest that worldwide all tea drinkers could benefit from protective cardiovascular effects exerted by tea.

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    • "Interestingly,each1-pointincreaseintheperceivedqualityscore ofthestudieswasassociatedwitha1mmHglargerreductionin theDBPeffectestimate.Thecovariateanalysisfoundno substantialinfluenceofamountofteaflavonoids,controllingfor caffeinecontent,orthedurationoftheintervention. Figure2.NetchangesinSBP(A)andDBP(B)inrandomizedstudiesofblackteaconsumption.Horizontallinesrepresent95%confidence intervals.Greydiamondsrepresentthepooledestimatesusingfixedandrandomeffectsmodelsrespectively.Grassietal.2009reportedbothoffice andambulatoryBP–bothsetsofdatawereincludedintheanalyses,buttokeeptheweightofthestudyproportionate,theweightofeacharmwas halved. "
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    ABSTRACT: Objective Epidemiological evidence has linked consumption of black tea, produced from Camellia sinensis, with a reduced risk of cardiovascular diseases. However, intervention studies on the effects of tea consumption on blood pressure (BP) have reported inconsistent results. Our objective was to conduct a systematic literature review with meta-analysis of controlled human intervention studies examining the effect of tea consumption on BP. Methods We systematically searched Medline, Biosis, Chemical Abstracts and EMBASE databases through July 2013. For inclusion, studies had to meet the following pre-defined criteria: 1) placebo controlled design in human adults, 2) minimum of 1 week black tea consumption as the sole intervention, 3) reported effects on systolic BP (SBP) or diastolic BP (DBP) or both. A random effects model was used to calculate the pooled overall effect of black tea on BP. Results Eleven studies (12 intervention arms, 378 subjects, dose of 4–5 cups of tea) met our inclusion criteria. The pooled mean effect of regular tea ingestion was −1.8 mmHg (95% CI: −2.8, −0.7; P = 0.0013) for SBP and −1.3 mmHg (95% CI: −1.8, −0.8; P<0.0001) for DBP. In covariate analyses, we found that the method of tea preparation (tea extract powders versus leaf tea), baseline SBP and DBP, and the quality score of the study affected the effect size of the tea intervention (all P<0.05). No evidence of publication bias could be detected. Conclusions Our meta-analysis indicates that regular consumption of black tea can reduce BP. Although the effect is small, such effects could be important for cardiovascular health at population level.
    Full-text · Article · Jul 2014 · PLoS ONE
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    • "Randomized controlled trial showed that black tea intervention can improve flow-mediated dilation which indicated a cardiovascular protective effect of black tea [6]. Hypercholesterolemia is closely correlated with risk of cardiovascular diseases, such as atherosclerosis and coronary artery disease [7]. "
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    ABSTRACT: Background & Aims The results of randomized controlled trials in relation to the effect of regular black tea consumption on serum cholesterol concentration were inconsistent. We aimed to investigate and quantify the effect of black tea consumption on serum concentrations of total, LDL and HDL cholesterol. Methods We systematically searched and identified relevant literatures in PubMed, Scopus and the Cochrane Library. Inclusion and exclusion of studies, data extraction, quality assessment and meta-analysis were conducted according to the PRISMA statement. Results Ten eligible studies with 411 participants were identified in the present meta-analysis. No significant heterogeneity was found between studies. Consumption of black tea significantly reduced LDL cholesterol concentration (-4.64 mg/dL; 95% CI: -8.99, -0.30 mg/dL; P = 0.036). No remarkable change was detected in total cholesterol (-2.04 mg/dL; 95% CI: -6.43, 2.35 mg/dL; P = 0.363) or HDL cholesterol (-1.15 mg/dL; 95% CI: -3.04, 0.75 mg/dL; P = 0.236). Subgroup analysis showed that the lowering effect on LDL cholesterol was more effective in subjects with higher cardiovascular risk. Conclusions Black tea consumption significantly lowered serum concentration of LDL cholesterol, especially in subjects with higher cardiovascular risk. Black tea intake did not impose obvious effect on serum concentrations of total and HDL cholesterol.
    Full-text · Article · Jun 2014 · Clinical Nutrition
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    • "Effects of juar tea on eEC-SOD levels and LDL oxidizability 411 beneficial effects of tea polyphenols on endothelial function (Jochmann et al. 2008; Grassi et al. 2009) might be mediated through eEC-SOD, which should be elucidated in future studies. Oxidative modification of LDL has been considered to play an important role in the development of atherosclerosis, and consistent with this idea, LDL oxidizability has been reported to be an independent predictor for CHD (Fraley and Tsimikas 2006). "
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    Preview · Article · Jan 2013 · International Journal of Food Sciences and Nutrition
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