Dietary Flavanols

Dietary Flavanols Study - Understanding the mechanisms behind cardiovascular disease reduction and cognitive enhancement by dietary flavanols

Cardiovascular disease is one of the leading cause of deaths worldwide. There is evidence to suggest that a diet high in flavanols (found in high concentrations in green tea), is related to reductions in deaths by cardiovascular disease. Blood viscosity affects the ability of blood to flow through the body, which can alter the risk of cardiovascular disease development. This study aims to test if the consumption of green tea acutely effects blood viscosity over 8 hours.

Purpose of the study

The aim is to understand whether there is an acute effect of green tea consumption on blood viscosity in people over the age of 65.

Who can take part in this study?

The study will recruit 35 adults, 65+ years old. Suitable volunteers should:

Have a body mass index between 19-30 kg/m².
Be non-smokers.

Exclusion criteria

You are not eligible to take part in the study if any of the following applies to you:

Participants under (BMI <18.5 kg/m2) or extremely over-nourished (BMI >30 kg/m2).
Participants on prescription medication for CVD or regularly taking blood thinning drugs such as aspirin.
Participants with a history of CVD or CVD in immediate family/ high resting blood pressure.
Participants with any food allergies/intolerances.
Participants with a history of metabolic diseases/ high resting blood glucose.
Participants with high resting levels of inflammatory markers (CRP).
Participants on hormone replacement therapy.
Participants with abnormal red blood cell count or low haemoglobin stores.
Participants with any known blood borne infections.

What will taking part in the study involve?

Screening visit

You will be invited to come for an initial screening visit at the Hugh Sinclair Unit of Human Nutrition in the Department of Food & Nutritional Sciences (University of Reading). The visit will take place in the morning, and you will be asked to arrive in an unfed state (fasted, not eating or drinking anything except water from 12 hours before the visit). First, the study will be explained in detail and your consent for participating in this study will be taken. After that, your weight, height and blood pressure will be measured before a small blood sample (4.5 mL, volume equivalent to just less than a teaspoon) is collected. The screening visit should take no more than 40 minutes and you will be provided with a light breakfast before you leave.

If you are found suitable for the study and are willing to participate, we will confirm with you your participation in the study. If you have any abnormal results, these will be reported to you and your GP.

Preparation for study visits

For 24 hours before your study visit you will be advised not to drink alcoholic or caffeinated beverages, to avoid aerobic/intense exercise and to not consume foods high in flavonoids (a list of foods will be provided). You will also be asked to avoid all food and drink, except water, from 8pm on the evening before each study visit until you are given the study breakfast the following day. You will be asked to keep a record of everything you eat and drink in the 24 hours leading up to your study visits.

Main study visits

Both study visits will last approximately 8.5 hours and will be identical in structure. For each visit you will be asked to come to the Hugh Sinclair Unit of Human Nutrition for the day where you will have unlimited access to drinking water and areas to work, read and use the internet between blood samples.

On arrival, we will ask you to give a 24-hour dietary recall. We will then take a resting blood pressure measurement, finger prick blood sample and a fasted blood sample (35.5 mL, approximately 2.4 tablespoons). We will then ask you to consume approximately 250ml of either hot water or green tea followed by a breakfast we will provide. We will then take a second blood pressure measurement and blood sample 2 hours after staring you drink (approximately 10:05am). You will then be provided with a lunch. We will take a final blood pressure measurement and blood sample 8 hours after starting the drink (approximately 4:05pm). This will be the end of the study visit, and you will be provided with a snack to take home. During one of the two visits only, we will also ask you to fill out a questionnaire about your habitual food intake. The two visits will take place at least a week apart and the exact process will be repeated. At the time of each blood sample, we will also ask for a spot urine sample.

Study contact

Please contact nutritionvolunteers@reading.ac.uk for more information about this study.