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The CIRCLES study


Investigating the health benefits of blueberries

The CIRCLES study is investigating:

Recruitment has now closed for our research study.

The effects of blueberry anthocyanins on insulin resistance and vascular, lung and cognitive function in a population with metabolic syndrome.

If you are interested in finding out more about the study, you can download and read our Participant Information Sheet by clicking the link below. If you've any questions, or would like to speak to a member of the study team, please call or email us using the information on the 'Contact' page.

You are being invited to take part in a research study. Before you decide, it is important for you to understand why the research is being done and what it will involve. Please take time to read the following information carefully and discuss it with others if you wish. Ask us if there is anything that is not clear or if you would like more information. This study has been approved by the NRES Research Ethics Committee (East of England, Norfolk) and the Research Governance Committee at the Norfolk & Norwich University Hospitals NHS foundation trust.

The Chief investigator of the study is: Professor Aedín Cassidy


What is the study about?

The study will test if natural compounds in Blueberries improve the function of our heart and blood vessels, and the way that our bodies control blood sugar levels.

Why do we think this is important?

The risk of heart disease and type 2 diabetes increases when our control of blood sugar and blood vessel function (e.g. control of blood pressure) become altered. Often, at the same time, other risk factors develop such as being overweight and having raised blood fats (like ‘bad’ cholesterol).

Critically, the risk of developing these diseases is much greater when several risk factors are found together. The presence of a combination of these risks factors is often described as ‘metabolic syndrome’.

Importantly, the NHS recently reported that UK adults are, on average, overweight (with ¼ of the population being obese) and that one in four people have metabolic syndrome. As a result, there is an increasing need to find ways to reduce heart disease and diabetes risk, and to improve the health of overweight and obese people who might also (often unknowingly) have poorer blood sugar control and raised blood pressure.

What will we do?

Our research intends to find out if making a change in diet, by consuming freeze-dried blueberry powder every day for 6-months, may help to reduce the risks linked to metabolic syndrome. We believe this is of great importance for the health and wellbeing of people with metabolic syndrome in the UK, and worldwide.

Why blueberries?

It is well known that what we eat and drink can have a major role in protecting us from disease. In particular, eating more plant based foods e.g. fruits, vegetables and wholegrains appear to reduce the risk of heart disease. This may be, in part, due to natural components in these types of food, such as a group of natural compounds called ‘flavonoids’.

Blueberries contain a type of flavonoid called anthocyanin which, when eaten frequently, is linked to a lower risk of developing type 2 diabetes. The intake of anthocyanins has also been linked to lower risk of some types of heart disease, such as stroke.

How do anthocyanins work?

Although we still have much to learn about anthocyanins, some studies have shown they can improve blood sugar levels and insulin sensitivity; this might explain, in part, the lower rates of diabetes in those who eat them more regularly.

After eating anthocyanins, some studies have also shown that blood vessels become more ‘relaxed’, which helps the blood flow more freely. This could help lower blood pressure which in turn might lower the risk of damage to our heart.

There is also some emerging evidence to suggest that eating anthocyanin rich foods might be linked to better lung function, liver fat levels (which itself, is linked to heart disease risk) and cognition.

However, much more research is needed in these areas to confirm these links.

We’d like your help to find this out.

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