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[Dr. N. Subramanian]

Q. I was a heavy coffee drinker, but now I'm getting off coffee by switching to tea, usually two to three cups of strong black tea a day (occasionally green tea instead). I feel less jittery, but now I hear the tannin in tea might be bad for me – true?

A. Tannins are found not only in tea, where they are indispensable to the production of tea's flavor and color, but they are found in many foods, such as cheeses and nuts, and in drinks such as wine. A plant contains tannin as a defense, to prevent it from being eaten. The bitter taste, as well as interference with starch digestion, tends to make the plant unpalatable to many animals, though tannins are not concentrated enough in tea to interfere with digestion if they are used in moderation. For some of us, the bitter taste of tannin is pleasurable. However, as always, people react differently to various food components, and for some, tannins cause headaches.
Tannins are touted as excellent antioxidants, promoted by the tea industry as well as wine and cheese makers. Catechin, one of several thousand proanthocyanidins or polyphenols, is a type of tannin peculiar to tea. Several of these proanthocyanidins are found to lower total cholesterol and improve the ratio of "good," or HDL, cholesterol to "bad," or LDL, cholesterol. They also seem to lower blood pressure, reduce the risk of cancer, stimulate the immune system, and have anti-bacterial properties.
High-tannin tea has also been shown to reduce the need for blood removal from people with iron overload, or hemochromatosis. Hemochromatosis arises from a genetic defect that allows uncontrolled absorption of iron. Iron overload, affecting one person in 200, is a major factor in congestive heart failure, a rapidly growing burden on the health care system. In one study, drinking tea with meals and without lemon or milk was shown to be effective in preventing iron absorption. In animal studies, liver iron stores increased significantly on an iron-enriched diet but not when the animals consumed the same diet supplemented with tea.
Tea and coffee both contain caffeine, a stimulant, but tea also has tannin and theanine, which are calming. The presence of these chemical compounds together in tea allows you to control its effect. When boiling water is poured onto the tea leaves, in the first two minutes all the caffeine is drawn out. At this point tea is most stimulating. During the next few minutes, tannin and theanine are gradually brought out of the tea leaves. After about five minutes this will tend to cancel out the effects of the caffeine and will make a more relaxing, calming tea. If you want only the calming effects from tea, discard the liquid from the first two minutes of steeping and use only the liquid from subsequent steeping, containing little caffeine and more tannin and theanine.
The question of whether tannins are connected to migraine headaches is still unresolved. Tannins are said to constrict blood vessels, but a migraine is usually caused by dilation of blood vessels, so how can tannins cause migraines? The answer may lie with the neurotransmitter serotonin. If tannin binds starches – needed by the body to produce serotonin – in people who are extremely sensitive to their serotonin levels, this lack of serotonin can lead to a migraine.
For those not prone to migraines, tea is certainly a much better choice than coffee.