I have heard that drinking tea is good for you and that it can help reduce the risk of heart disease. Is this true? 

This answer is brought to you by many of the Australian nutrition professionals who regularly contribute to a nutrition email discussion group.

Tea has been drunk in China for well over 4,000 years. Legend has it that in 2737 BC, Emperor Shen-Nung drank, and enjoyed, the dark liquid that resulted when tea leaves accidentally fell into boiling water. From that royal beginning, tea drinking gradually spread around the world until it is now the most commonly drunk non-alcoholic beverage.

Tea leaves are the dried leaves of a species of Camellia (not the same species as those grown by many people in their gardens, but a close relative). There are two main types of tea - green and black. These come from the same plant, but have been treated differently: green tea is heated soon after picking and is not subjected to further processing; black tea, on the other hand, is dried and then exposed to the air before it is heated. Consequently, green and black tea differ noticeably in appearance, taste and chemical composition. Green tea is more common in Asia, while black tea is the tea of choice for most people in Western countries.

Both green and black tea contain caffeine, a drug that has a mild stimulating effect. The quantity of caffeine provided by a cup of tea depends on its strength: the stronger the 'brew', the greater the quantity of caffeine. A medium-strength cup of tea will provide about one third as much caffeine as a cup of percolated coffee, and about two thirds as much as a cup of instant coffee. Caffeine intakes that result from drinking four or five cups of tea each day are not associated with any harmful effect to health in adults. Because it is not known if caffeine is absolutely harmless to the unborn baby, pregnant and breastfeeding women should probably restrict intake of caffeine (e.g. to that provided by three or four cups of tea per day).

For several years it has been suspected that drinking tea might help protect against heart disease. One way in which tea could be protective is through the effects of 'antioxidants' - chemicals in tea that help protect blood cholesterol (among other blood components) from being oxidised. Oxidation of cholesterol turns it into a form that is strongly associated with increased risk of heart disease. This antioxidant effect of tea may also be helpful in reducing the risk of some cancers. There are other ways in which tea may be beneficial to health, too. For example, the same chemicals that appear to protect blood cholesterol also reduce the likelihood that blood will clot in the arteries of the heart (the immediate cause of most heart attacks).

The evidence, while not overwhelming, is quite strong that tea may be beneficial to health generally, and to heart health in particular. Population studies have usually shown that tea drinkers have significantly less risk of heart disease than people who do not drink tea. Of course, other factors could be important here. For example, coffee drinkers tend to smoke more than tea drinkers, so the association of tea with better health may be a statistical illusion. However, studies in test tubes have shown that several chemicals in tea will reduce the oxidation of cholesterol.  Also, studies in which people drank either tea or water showed that, shortly afterwards, the tea drinkers had lower levels of oxidised cholesterol in their blood than those who drank plain water.

One question that remains to be resolved is 'what is the effect on health of adding milk to tea?' Early studies indicated that milk might interfere with the antioxidant activity of tea, but more recent results suggest that milk is unlikely to reduce the antioxidant effect of tea in the body. It appears that green tea, black tea, and black tea with milk all have similar health-promoting effects. Population studies suggest that as little as one cup of tea per day confers benefits.

One point worth noting is that drinking tea with a meal will interfere with iron intake from foods of plant origin. Unless you have a problem with too much iron in the blood (a condition known as 'haemochromatosis', which affects about one person in 300) your iron status will be better if you drink tea between meals rather than with a meal.

It is known that a diet that is high in fruits, vegetables and whole grain cereals, and relatively low in fat (especially saturated fat), combined with a lifestyle that includes daily moderately-vigorous activity, is very likely to be health-promoting. Current evidence suggests that a 'cuppa' (or better still, several) each day may even further reduce the risk of diseases such as heart disease.

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[Date issued: August 1999]

Disclaimer: This material is provided on the basis that it constitutes advice of a general nature only. It is not intended to replace the advice of a physician or a dietitian.