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Study Title and Description
The acute effect of green tea consumption on endothelial function in healthy individuals.
Key Questions Addressed
| 1 | For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on cardiovascular outcomes? |
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Primary Publication Information
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| Title | The acute effect of green tea consumption on endothelial function in healthy individuals. |
| Author | N Alexopoulos,C Vlachopoulos,K Aznaouridis,K Baou,C Vasiliadou,P Pietri,P Xaplanteris,E Stefanadi,C Stefanadis, |
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| Year | 2008 |
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Secondary Publication Information
There are currently no secondary publications defined for this study.
Extraction Form: Cardiovascular Design
| Question... Follow Up | Answer | Follow-up Answer | |
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| What outcome is being evaluated in this paper? | Cardiovascular |
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| What is the objective of the study (as reported by the authors)? | This randomized, sham procedure-controlled, crossover (three-arm) study was undertaken to evaluate the acute effect of green tea and its caffeine content on flow-mediated dilation (FMD) of the brachial artery in healthy individuals. Furthermore, we sought to test the hypothesis that any effect would be associated with changes in inflammatory or oxidative status. |
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| Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods) | Study population: The study population consisted of 14 healthy individuals [age 30 +/-3 years, nine men].]. Each of them was studied on three separate occasions. All patients were nonobese and they did not have hypertension, diabetes, hyperlipidemia, or a family history of premature vascular disease. Seven patients (50%) were smokers. They were clinically well and taking no regular cardiovascular medications or antioxidant vitamin supplementation. Patients abstained from caffeine and ethanol intake and from smoking for at least 12 h, and from flavonoid-containing food for at least 24 h before each session. Female participants were examined during the follicular phase of the menstrual cycle and none was on oral contraceptives. Study design: The studies were carried out using a randomized, single-blind (operator), sham procedure-controlled, crossover design. Patients were studied on three separate days on which they took either: (a) 6 g of green tea (Lipton Tea Company, Crawley, UK) added in 450 ml of boiled water for 5 min, (b) 125 mg of caffeine (the amount contained in 6 g of green tea; see below ‘measurement of caffeine contained in tea’) diluted into 450 ml of boiled water, or (c) 450 ml of hot water. After a 20-min rest period in the supine position, baseline measurements for the evaluation of endothelial function were taken. Then, the patients were randomized to the different arms of the study and measurements were repeated at 30, 90, and 120 min after baseline measurements. Venous blood for measuring high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (Il-6), interleukin-1b (Il-1b), total antioxidative capacity, and total lipid peroxides was drawn at baseline and at 120 min when peak plasma flavonoid concentration is anticipated. Measurement of caffeine contained in tea: The caffeine content in five samples of green tea prepared in an identical manner as in the study sessions was analyzed for caffeine content in the General Chemical State Laboratory, Athens, Greece using HPLC chromatography. The 450 ml (6 g of green tea) beverage contained 128 +/- 3 mg of caffeine. Evaluation of endothelial function: FMD is predominantly dependent on nitric oxide (NO) release by the endothelium and has been used as an estimate of endothelial function. Resting and hyperemic arterial diameters and flows and FMD of the conduit brachial artery were determined by using a high-resolution, linear array ultrasonic transducer of 7.5–10.5MHz (Hewlett-Packard, Sonos 5500, Andover, Massachusetts, USA). The brachial artery was scanned in the longitudinal plane, above the antecubital fossa. Then, reactive hyperemia was induced by inflating a forearm occlusive cuff at suprasystolic levels for 5 min. Brachial artery was continuously scanned from 30 s before to 90 s after cuff deflation. Hyperemic velocity was assessed by a Doppler signal obtained within the first 15 s after cuff deflation. At least 10 min after the 120 min cuff deflation, endothelium-independent, nitrate-induced dilatation (NID) was measured after delivering a single (0.4 mg) dose of nitroglycerin spray sublingually. |
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| How many outcome-specific endpoints are evaluated? | 4 |
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| What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) | Blood pressure (SBP and DBP) |
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| List additional health endpoints (separately). 2 | Endothelial function (flow-mediated dilatation [FMD]) |
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| List additional health endpoints (separately).3 | Inflammatory status (high-sensitivity C-reactive protein, interleukins Il-6 and Il-1b) |
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| List additional health endpoints (separately).4 | Oxidative status (total plasma antioxidative capacity, total plasma antioxidative capacity, and total plasma oxidative status/stress) |
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| List additional health endpoints (separately).5 |
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| List additional health endpoints (separately).6 |
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| Clinical, physiological, other | Physiological |
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| What is the study design? | Controlled Trial |
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| Randomized or Non-Randomized? | RCT |
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| What were the diagnostics or methods used to measure the outcome? | Objective |
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| Optional: Name of Method or short description | Resting and hyperemic arterial diameters and flows and FMD of the conduit brachial artery were determined by using a high-resolution, linear array ultrasonic transducer of 7.5–10.5MHz (Hewlett-Packard, Sonos 5500, Andover, Massachusetts, USA). Serum levels of hs-CRP were measured by immunophelometry (Dade Behring, Marburg, Germany). IL-6 and IL-1b were measured using enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, Minnesota, USA). The plasma total antioxidative capacity (TAC) was measured using ImAnOx kit, and the total plasma lipid peroxides were measured using PerOx kit. Both are photometric enzyme-linked immunosorbent assay sandwich tests provided by Immundiagnostik AG, Stubenwald- Allee 8a, D 64625 Bensheim, Germany. |
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| Caffeine (general) | Caffeine (general) |
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| Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other? | Tea |
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| Measured or self reported? | Measured |
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| Children, adolescents, adults, or pregnant included? | Adults |
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| What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) | This was a randomized cross-over study. Subjects served as their own baselines. Hot water was used as the control substance. |
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| What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods) | Baseline parameters between the three sessions were compared using one-way analysis of variance. Changes in hs-CRP, Il-6, Il-1b, TAS, TOS, or NID between tea or caffeine session and sham procedure session were compared using the Student’s t -test for paired measures. To evaluate the composite effect of tea, or caffeine versus placebo over time on all the other variables, a 4 x 2 analysis of variance for repeated measures was performed [4 periods (baseline, 30, 90, and 120 min) x 2 interventions (tea or caffeine vs. placebo)]. |
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| What conflicts of interest were reported? | Authors reported they had no conflicts of interest. |
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| Refid | 18525384 |
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| What were the sources of funding? | No information was provided. |
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Results & Comparisons
No Results found.
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