Flavonoids are a group of around 4000 chemicals found in plants. Epidemiological studies suggest that high intakes of plant foods are beneficial to the health, and this may relate to the presence of flavonoids. Chemical analysis of flavonoids show that they are potent antioxidants in humans and consumption of flavonoids decreases systemic oxidation. For this reason flavonoids may protect from cardiovascular disease by protecting arteries from damage.
Berries are a rich source of flavonoids. The flavonoids in berries are what give the skins their dark blue, red and purple colours. This relates to the way the flavonoids absorb ultraviolet light. The flavonoids in berries give the plants protection from direct sunlight, pollution, and other free radicals, by acting as antioxidants to stabilise plant tissues. When we eat the flavonoids in berries we obtain that protection in our cells and in our blood.
Berries are a popular food because they taste good. This relates to the sugar content of the berries. Although sugar in excess is potentially a cause of cardiovascular disease, this is not the case with the sugar in berries. Because the sugar is contained in fibrous cells walls, the sugar in berries is inhibited from interacting with digestive enzymes. This delays or inhibits the absorption of the sugar and produces favourable effects on blood glucose.
The flavonoids in berries are called anthocyanins. Studies show that when we eat berries the anthocyanins appear in our blood, and here they can have an antioxidant effect. Anthocyanins are slightly different to other flavonoids because they are absorbed from the stomach. In addition, they may be absorbed in their glycoside form, which means they have a sugar attached to their structure. These differences may give anthocyanins different properties to other flavonoids.
Recent evidence suggests that free radicals may be a cause of cardiovascular disease. Free radicals can damage arteries because they inhibit an enzyme called nitric oxide synthase. This enzyme normally makes nitric oxide, a potent relaxant in the artery walls. Without the ability to relax, arteries become inelastic and do not respond with dilation when blood flow occurs. This raises blood pressure and may damage the lining of the arteries through pressure changes.
Research from the nutritional literature shows that berries lower blood pressure. They are able to do this because of the flavonoids they contain. When the flavonoids are absorbed, they enter the blood and prevent free radicals inhibiting nitric oxide synthase. This allows normal production of nitric oxide and this has a blood pressure lowering effect. Regular consumption of berries may therefore be beneficial at reducing the risk of cardiovascular disease.