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Flavonoids: an introduction

Polyphenols, and flavonoids in general, are frequently mentioned as reasons why some food might be "super". Watch David Field explain more.
-Hello. I’m David Field from the University of Reading in the UK. In this first video, I’m going to just do a general introduction to a class of phytochemicals called flavonoids. The reason that plants synthesize flavonoids is in response to various stressors that they face in their environment. For example, anthocyanin which is produced by blueberries and gives them the purplish bluish color that you’re familiar with, is produced in response to ultraviolet light from the sun and also to cold. When there is more sun, there is going to be more anthocyanin in the blueberries and also if there’s more frost or cold at night, they’ll be more anthocyanin because that molecule protects the berries against both damage from the sun.
It acts as a sunscreen but also protects against frostbite if you like. There is however one more function of flavonoids for plants that doesn’t come under the general heading of a way of defending against stressful environmental factors and that is that because of the bright colors that flavonoids can give to the fruits, leaves and flowers petals of plants. They also act to attract pollinating insects such as bees to the plants. Now a little bit of the history. What triggered scientists to become interested in flavonoids few decades ago. Well, observations were made about a group of people known as the Kuna, who live in Panama in Central America.
The majority of the Kuna live on the mainland of Panama but a significant minority of them live on some small, endemic looking islands just off the coast of Panama on the San Blas Islands. The Kuna living on the islands seem to have much lower rates of cardiovascular problems and also diabetes than the Kuna who were living on the mainland of Panama. Initial hypotheses about why this might be included things like, well, it might be more stressful in the mainland than it is on the islands. It was noticed that the Kuna who live on the islands have got the habit of drinking every day a cocoa drink which is pretty raw.
It’s not very processed which is significant because that means that the flavonoids from the cocoa won’t have been altered or denatured by the heat or other source of processing. They worked out that they were getting a dose of over 900 milligrams a day on average of cocoa flavonoids. This was thought could perhaps be the thing that accounted for the difference in cardiovascular problems and diabetes between the Kuna on the islands and the Kuna living on the mainland. Further some tests were then done on the blood pressure of the Kuna living on the islands, finding that they typically have lower blood pressure.
This suggested that their endothelial function might be different and better in some way to that of the Kuna living on the islands. The endothelium is a thin layer of cells that lines all the blood vessels in the body. The endothelium has the effect of controlling the smooth muscles that surround the blood vessels to produce the contraction and the dilation that regulates the flow of blood. Down at the level of detail how this happens is the endothelium produces a signalling molecule nitric oxide which is actually a gas. It turns out that flavonoids and cocoa flavonoid in particular, in this case, increase the amount of nitric oxide that is produced in the body particularly by the endothelium.
This has the effect of greater relaxation of blood vessels and, therefore, greater blood flow. One of the consequences of that is a fall in blood pressure. Scientists got quite excited about that, not just because of the benefits for blood pressure, which obviously helpful in and of themselves, but also because the mechanism that the signaling molecule the nitric oxide has other roles in the body. It’s not just involved in this single pathway by which the muscles relax and contracts surrounding the blood vessels, it’s also acting as a signaling molecule for various processes in the brain, and in the brain actually even acts as neurotransmitter.
This led to the idea that we’re going to talk about in my next video is that there might well be positive effects for the brain of consuming dietary flavonoids just as there are for the cardiovascular system.

What are flavonoids?

In the first week we already mentioned the fact that some antioxidative or anti-inflammatory property of foods is used as a reason to elevate them to “super” status.

Flavonoids are a class of molecules and have been extensively studied: they possess antioxidant properties in vitro and in animal models, but they have also been linked to other beneficial effects, starting with a reduction in blood pressure and increased cardiovascular health.

These molecules are widespread in nature – they are found, for instance, in apples and citrus fruits, in berries and tea, in cocoa and some green vegetables. Despite this fact, flavonoids are poorly absorbed by the digestive system and are metabolized quickly: this is why scientists are interested in both the long and short term effects of diets particularly rich in them.

In this first video, we will start our discussion of flavonoids with the example of a population that traditionally consumes a flavonoid-rich beverage every day, the Kuna living in San Blas (Panama), and with the mechanism that could be responsible for the beneficial effects of flavonoids on our cardiovascular system. In the next activity, we will continue this discussion and move on to other areas where flavonoids might exert a beneficial effect: brain health and cognitive functions.

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