Berry good - understanding the role of flavonoids in our diet
We are often urged to eat our five a day and it’s a concept that endures around much of the world.
Advice from the World Health Organisation recommends adults eat a minimum of 400g of fruit and vegetables per day in order to maintain a healthy, balanced diet.
Research shows there are significant health benefits from consuming a diet rich in fruit and vegetables; a higher intake can help lower the risk of a number of chronic conditions including diabetes, heart disease, stroke and some cancers.
In fact recent evidence suggests that a healthy diet should contain more than five portions a day, with guidelines in Australia and the US being updated to reflect this. Yet government guidelines can prove hard to follow with less than 30% of the population meeting healthy eating targets in the UK.
What if we could know exactly which fruit and vegetables were most beneficial for health, what chemicals they contain that are specifically able to reduce the risk of chronic disease and how much we should eat of them in order to truly impact on our health?
Professor Aedín Cassidy’s research is focussed on identifying which food constituents might be important for health and on providing evidence to help shape dietary advice, optimising the benefits of fruit and vegetable intake in reducing the risk of developing diabetes and heart disease.
THE ROLE OF FLAVONOIDS
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Evidence shows that what we eat plays a key role in maintaining optimal health and reducing our susceptibility to developing chronic diseases like diabetes and heart disease.
Yet poor diet still contributes one of the largest economic burdens to the NHS, costing £5.8 billion per year (Scarborough 2011).
Despite improvements in treatments resulting in significant declines in mortality rates it is clear that prevention also plays a key role in the future management of disease, and that good nutrition is essential to this.
Professor Cassidy's research highlights the beneficial effects of naturally occurring compounds in fruits and vegetables called flavonoids, as likely constituents in lowering disease risk.
As part of a long-term collaboration with Harvard, Cassidy’s recent findings have led the way in showing that several specific flavonoid classes (those present in berries and citrus fruits) are associated with a lower risk of having a heart attack, stroke, or developing type 2 diabetes.
Professor Cassidy has shown that higher intakes of one group of flavonoids, called anthocyanins, can impact on a whole range of health issues – including hypertension, myocardial infarction, and type 2 diabetes.
High blood pressure affects around ten million people in the UK. Despite being relatively common, if left untreated hypertension can lead to serious health issues including heart disease and stroke.
Professor Cassidy's work with Harvard shows that eating just a few portions of anthocyanin-rich foods every week is associated with a reduced risk of developing hypertension. By studying the habitual diet of more than 134,000 women and 23,000 men (who did not originally have hypertension) over a period of 14 years they were able to show that simple dietary change like adding a few portions of berries to the habitual diet had the potential to have a significant impact on preventing the development of hypertension.
"Anthocyanins are readily incorporated into the diet as they are present in many commonly consumed foods,” comments Professor Cassidy “Blueberries were the richest source in this particular study as they are frequently consumed in the US. Other rich sources of anthocyanins in the UK include blackcurrants, blood oranges, aubergines and raspberries”
Myocardial infarction (MI), or heart attack as it is more commonly known, is one of the leading causes of death worldwide. An expanding ageing population and increasing prevalence of obesity means preventive medicine is becoming increasingly important, and an optimised diet is central to improving cardiovascular health.
A ‘heart-healthy’ diet which favours healthy fats, nutrient rich fruit and vegetables, and fibre can help lower cholesterol, control blood pressure and blood sugar levels and reduce risk of heart disease or stroke.
"We have shown," explains Professor Cassidy, "that even at an early age, eating more blueberries and strawberries may reduce the risk of a heart attack later in life."
In a collaboration with Harvard they conducted the first population-based study to look at the impact of diet, specifically flavonoids, on risk of having an MI in younger and middle-aged women. Cassidy adds, "Blueberries and strawberries contain high levels of compounds called anthocyanins that have cardiovascular benefits, and our study shows that women who ate at least three portions per week had a lower risk of having a heart attack."
TYPE 2 DIABETES
The number of people with type 2 diabetes is rising rapidly, with over 3.5m in the UK alone. Often diagnosed in older people and associated with obesity, left untreated diabetes can result in significant ill-health. People with diabetes are also up to five times more likely to develop cardiovascular disease.
Professor Cassidy’s department performed a year long clinical trial in 93 medicated postmenopausal women with type 2 diabetes in order to find out whether flavonoids could help to reduce risk factors related to controlling blood sugar levels or having a heart attack or stroke. Risk factors included insulin levels, blood pressure and pulse wave velocity as a measure of how flexible our arteries are.
In a randomised controlled trial, where half the group ate flavonoid-enriched chocolate every day while the other half of the group ate a similar placebo chocolate bar with no flavonoids, the results showed that flavonoid intake lowered the women’s insulin levels and improved their vascular health.
In collaboration with TwinsUK, based at King’s College London, Professor Cassidy conducted complementary population based studies analysing the relationship between habitual flavonoid intakes and blood levels of glucose, insulin and markers of inflammation.
The research looked at the benefits of eating certain sub-groups of flavonoids, focussing mainly on anthocyanins, found in berries, red grapes, wine and other red or blue-coloured fruits and vegetables.
"This is one of the first large-scale human studies to look at how these powerful bioactive compounds might reduce the risk of diabetes,” explained Professor Cassidy. “Laboratory studies have shown these compounds regulate blood glucose and insulin levels – with the potential to reduce the risk of type 2 diabetes. But until now little has been know about how habitual intakes might affect insulin resistance and inflammation in humans."
"We found that those who regularly consumed more anthocyanins had lower insulin resistance. High insulin resistance is associated with an increased risk of developing Type 2 diabetes, so what we are seeing is that people who eat foods rich in these compounds - such as berries, grapes, wine - are less likely to develop the disease.
"We also found that those who ate the most anthocyanins were least likely to have chronic inflammation - which is associated with many of today's most pressing health concerns including diabetes, obesity, cardiovascular disease, and cancer.
"What we don't yet know is exactly how much of these compounds are necessary to potentially reduce the risk of type 2 diabetes."
LET FOOD BE THY MEDICINE?/FOOD FOR THOUGHT?
Although it has been known for a long time that fruit and vegetables are key ingredients for health, the link between a higher intake of flavonoids - especially anthocyanins – and improved health, especially heart health, is growing.
Prof Cassidy hopes that by further understanding the role compounds such as anthocyanins play in maintaining health, her research will be able to provide crucial evidence to inform global nutrition guidelines, helping to combat the critical rise in chronic disease.
Aedin Cassidy is a former Professor of Nutrition, Norwich Medical School. Her current role is Director of Interdisciplinary Research, IGFS, Queen's University Belfast