Investigating the Effects of Green Tea on Blood Viscosity

Overview

A diet high in flavonoids is becoming more established as beneficial to human health. Recent data suggest that the regular consumption of flavanols can reduce the numbers of deaths by cardiovascular disease at a population level. The mechanisms for these reductions in deaths by cardiovascular disease are still debated and little is known about their impacts on factors affecting blood viscosity. The metabolism of flavanols is complex, with different metabolites being predominant in the blood at different time points. Therefore, in this study, we will investigate the effects of green tea, a well-known source of flavanols, on blood viscosity at different time points. This will be assessed in healthy individuals with no history of cardiovascular disease aged 65+ years old. Blood viscosity will be measured before, and 2hours and 8hours after the consumption of green tea.

Participants will first be screened via a questionnaire on RedCap. This will include a list of exclusion and inclusion criteria. Examples of what will be included are: must be a non-smoker, no history of CVD or CVD in immediate family, no history of metabolic diseases, no food allergies, or intolerances and not be on any medication for cardiovascular purposes (e.g. aspirin or blood pressure medication). Before confirmation, a screening visit will be undertaken where checks for regular haematocrit, blood pressure, plasma triglycerides, blood glucose and inflammatory markers and BMI will be taken. This will involve a 4.5 ml blood sample. Additionally, the research nurse will assess the potential participant's veins, and participants who do not have 2 'good' veins for giving blood will be excluded from the trial. Following recruitment, participants will be asked to follow a set of criteria for the 24 hours prior to participating in the study. This will include, following a low polyphenol diet and not consuming any over the counter medication, caffeine or alcohol for 24 hours prior to participating. Participants will also be asked to attend fasted for 12 hours. Participants will also be asked to not take part in any vigorous/aerobic exercise in the 24 hours leading up to the study. Following recruitment, and on arrival, participants will be asked to confirm they have followed the requirements for the previous 24 hours and full informed consent will be obtained from the participant. Participants will complete a spot urine test to measure osmolality as a measure of hydration. Participants will be asked to sit in a rested position for 15 min prior to each blood sample. Blood pressure will then be measured followed by a blood sample (17.5ml). The blood sample will be passed through the viscometer to assess whole blood and plasma viscosity and part of the blood sample will be used to measure haematocrit, inflammatory markers and blood lipids. The participant will then be given 200 mL green tea. They will be asked to consume this within 15 minutes. The intervention will be provided in an opaque cup with a lid on and the participant will be asked not to remove the lid so that the contents is not revealed to them. This will be followed by a low flavonoid breakfast. The same blood sample and urine test will then be taken at 2 hours and 8 hours after the start of consuming the drink, and these will be processed in the same way. A low flavonoid meal will also be provided between the 2- and 8-hour blood sample. A second visit will involve the exact same protocol; however, the participants will be given hot water as a control condition. On the first of two visits, the participant will be asked to fill out a food frequency questionnaire. The order of green tea/control visits will be randomised and counterbalanced. In the 12-hours leading up to the visit, participants will be asked to consume 500 mL of water (a bottle will be provided). Throughout the visit, participants will be provided with unlimited water to drink and the total volume that has been consumed between each blood sample throughout the study will be recorded. On the second visit, the participant will be asked to replicate this amount.