How to enjoy the many health benefits of tea

Tea is the world's most popular non-alcoholic beverage. Most tea is grown in India, Sri Lanka, China, Japan, Taiwan and Indonesia from a shrub in the camellia family. Like coffees, the best-quality teas are grown in the shade at high altitudes, and the finest leaves are plucked from the youngest shoots and unopened leaf buds, which also contain the highest levels of phenols, enzymes and caffeine. Researchers are discovering evidence that tea may offer not only soothing warmth and mild stimulation, but also health benefits. Here are some tips on enjoying those benefits.

Tea contains hundreds of compounds, including various flavonoids, a class of chemical with powerful antioxidant properties. A subclass of flavonoids, the catechins, is responsible for the flavour as well as many of the beneficial health effects of tea. The extent to which these compounds are present in the final beverage depends on how the leaves are processed.

• To make black tea, the dried leaves are crushed to liberate enzymes, which react with the catechins over a few hours to produce changes in colour and flavour. This is often referred to as "fermentation."
• Green tea is not fermented, it is made by first steaming the leaves to halt any enzyme activity.
• Oolong tea is partially fermented.
• The highest concentration of catechins is found in green tea, although black tea is also a good source.
• Brand-name teas are mixtures of as many as 20 different varieties of leaves, blended to ensure a consistent flavour.

Researchers at Tufts University in Boston compared the ORAC capacity of tea with 22 vegetables. ORAC refers to the oxygen radical absorbance capacity, a measurement of the total antioxidant power of foods and other chemical substances. The higher the ORAC score, the greater its antioxidant capacity.

• Although there was variation among various teas, the highest scoring teas were green tea and black tea, brewed for five minutes — they outranked the best fruits and vegetables. While this doesn't suggest that tea should replace fruits and vegetables in daily consumption, it does underline the positive effects of this drink.

• A cup of hot brewed tea has only two calories and — with one exception in green tea — no appreciable vitamins or minerals, except for fluoride.

• Green tea contains vitamin K, a nutrient needed for normal blood clotting.

Researchers report in the Proceedings of the National Academy of Sciences that they have found a chemical in tea that boosts the body's defense against disease fivefold. They say they isolated from ordinary black tea a substance called L-theanine, also found in green and oolong tea.

• L-theanine is broken down in the liver to ethylamine, a molecule that primes the response of an immune blood cell called the gamma-delta T cell.
• Gamma-delta T cells in the blood are the first line of defense against many types of bacterial, viral and parasitic infections. T
• hey might even have some anti-tumour activity. The T cells prompt the secretion of interferon, a key part of the body's chemical defense against infection.