The Antioxidant Properties of Tea

Customers Experience Marked Improves From Drinking 2-4 Cups a Day!

Increasing evidence is highlighting the role antioxidants play in protecting against certain conditions such as heart disease, stroke and cancers. It has been proposed that the mechanisms leading to these diseases may be promoted by free radicals and that antioxidants may oppose the action of these molecules. In addition to the well known antioxidants such as Vitamins C and E, there is growing research demonstrating the potentially beneficial effects of plant-derived antioxidants, polyphenols, found in fruits, vegetables, nuts, cereals and drinks such as tea and red wine.

Free Radicals Explained

Free radicals are unstable molecules that include the hydrogen atom, nitric oxide (NO) and reactive oxygen species. These naturally occur in the body as a result of chemical reactions during normal cellular processes. They can also be formed in response to excess pollution, too much UV sunlight and exposure to cigarette smoke. In an attempt to stabilize, they attack other molecules in the body potentially leading to cell damage and triggering the formation of another free radical resulting in a chain reaction. Some scientists believe that this type of free radical action has been implicated in certain chronic and aging diseases such as cancer, heart disease, stroke, rheumatoid arthritis, cataracts and Alzheimer’s disease.

Sources of Dietary Antioxidants

Traditionally dietary antioxidants were thought of as Vitamin E and C and the carotenoid b- carotene. In recent years there has been particular interest in the antioxidant activity and health benefits of other phytochemicals. Table 2 lists two examples of phytochemicals and their food sources. Tea has one of the highest total flavonoids contents of all plants at 15% of the leaf by dry weight and is also the major source of flavonoids in the UK diet, providing approximately 80% of dietary flavonoids for the population as a whole.According to a survey conducted by MAFF, approximately 30mg of flavonoids/ person/ day is consumed in the UK.

Tea Flavonoids

The types and amounts of flavonoids present in tea will differ dependent on the variety of leaf, growing environment, processing, manufacturing, particle size of ground tea leaves and infusion preparation. Green teas contain more of the simple flavonoids called catechins, while the oxidization that the leaves undergo to make black tea converts these simple flavonoids to the more complex varieties called theaflavins and thearubigins. Tea flavonoids are water-soluble and one study has shown that a cup of UK tea that has been allowed to brew for 40-60 seconds will typically deliver approximately 140mg of flavonoids, whilst a second carried out by the UK Tea Trade Technical Committee. Using typical UK consumer brewing conditions and encompassing the range of blends and bag weights commonly on sale in the UK gives a figure of 125mg/ 235ml serving. The longer the tea is left to brew, the higher the concentration of flavonoids. Tea flavonoids, in both green tea and black tea, demonstrate antioxidant activity and while not a replacement for fruit and vegetables, the antioxidant activity of tea has been compared to that of fruit and vegetables in a number of studies. One study concluded that 3 cups of tea a f day has approximately the same antioxidant power as eating six apples. Another study found that one or two cups of tea has the same ‘radical scavenging capacity’ as five portions of fruit and or vegetables 400mg vitamin C equivalents. In fact many common flavonoids are several times more potent than Vitamin C or E.

Health Benefits of Tea Flavonoids

The antioxidant activity and potential health benefits of flavonoids has been well documented and extensively reviewed in the literature. Interest in this field has resulted in a growth in the amount of research being undertaken in the area of flavonoids and heart disease, cancer and oral health. Furthermore, because of the accumulating evidence to suggest that oxidative stress plays a pivotal role in neurodegenerative diseases, the positive effect of tea’s polyphenols are now being considered as possible neuroprotective agents in progressive neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. Recent epidemiological studies have shown a reduced risk of Parkinson’s disease associated with the consumption of 2 or more cups of tea a day as well as a significant reduction of Parkinson’s disease risk in tea drinkers in a Chinese population. As well as antioxidant properties, animal and in-vitro studies suggest that certain polyphenols found in tea may have a protective role through their action on cell signaling pathways as well as their influence on the mortality of neuronal cells. However, well-controlled, in vivo studies are required to further understand the action of tea polyphenols in the brain.

Absorption of Tea Favonoids

Until recently the majority of the research demonstrating the antioxidant activity of tea flavonoids was either using animal models or laboratory cellular studies. Increasing numbers of human studies are now concluding that the body does in fact absorb some of these antioxidants. For example, enhanced plasma levels of catechin have consistently been foundfollowing the consumption of green and black tea, ranging from0.63–1.8 µmol/L for green and 0.2–0.34 µmol/Lfor black tea. The plasma levels peaked after 1.5–2.6hours and were back to baseline within 24 hours. Further research is currently being undertaken on the metabolism, distribution and excretion of tea flavonoids and its metabolites. As well as being absorbed these flavonoids demonstrate anti-oxidative potential in vivo.A number of studies have shown that plasma antioxidant activity peaks 30-60 minutes after moderate tea consumption (1-6 cups). Despite plasma catechin levels being higher following the consumption of green tea compared to black tea, their antioxidant activity is similar. This finding has led to the suggestion that the theaflavins and thearubigens in black tea also have anti-oxidative properties.

The addition of milk to tea, as enjoyed by the majority of the UK population, does not appear to affect the antioxidant activity of the tea flavonoids.

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