GREEN and black teas are made from the same leaves but their preparation before they reach the shops is different. The leaves used for green tea are steamed or dried at high temperatures; those destined to become black tea are treated by enzymatic oxidation. As a result the biochemical composition differs.

Both forms are rich in the antioxidants known as flavonoids. Research in the past 20 years has demonstrated that both reduce the incidence of cardiovascular disease, including coronary arterial troubles and ischaemic strokes.

The average cup of black tea contains as high an anti- oxidant level as a standard helping of strawberries, blueberries or cranberries. The British cuppa has twice the antioxidant content of an average-size apple.

The importance of this latest Japanese paper — published in JAMA, a respected American journal — is that it seems to show that green tea drinkers, such as the Japanese, derive a greater benefit from their daily intake than Europeans do from their daily black tea. The differences in the methods of preparation of the tea leaves from the natural leaf result in green tea having more flavonoid catechins, whereas black tea has greater amounts of theaflavins and other polyphenols.

The catechin antioxidants thought to account for the health-giving powers of green tea reduce coronary heart disease and ischaemic strokes by affecting the structure of the arterial wall, possibly causing some arterial dilation, and by making the blood less likely to clot.

They may alter the proportion of the total cholesterol carried as high-density lipoprotein, the “good” cholesterol, as opposed to LDL, the pernicious cholesterol.

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