Tea
White tea, green tea, black tea, and oolong tea all come from the same plant, Camellia Sinensis. What differentiates one tea from another is the way the tea leaves are processed.
White tea (which actually brews up slightly pinkish) is made from tea buds and very young leaves which are steamed or “fired” (heated) and then dried. Green teas are brewed from slightly more mature leaves, which are allowed to wither before they are steamed or dried.
Oolong teas are made from teas allowed to dry in the air for a longer time than white or green teas (but for less time than black teas) before being steamed or fired. Leaves meant for black teas are rolled and broken up to allow full drying before they are processed. During fermentation polyphenoloxidase, an enzyme in the leaves, hastens the oxidation of phenols in the leaves, creating brown pigments that darken the leaves and intensify their flavor. (Souchong, pekoe, and orange pekoe are terms used to describe grades of black-tea leaves. Souchong leaves are round; orange pekoe leaves are thin and wiry; pekoe leaves are shorter and rounder than orange pekoe.)
The tea plant is a good source of the B vitamin folate, and it is high in fluorides. It is not uncommon to find a tea plant with a fluoride concentration of 100 ppm (parts per million). By comparison, fluoridated water is generally 1 ppm fluoride. The USDA estimates that a six-ounce cup of tea prepared with tap water may provide 663 mcg fluoride.
Like coffee and chocolate, tea contains the methylxanthine stimulants, caffeine, theophylline, and theobromine. (Coffee has more caffeine; tea has more theophylline; and chocolate has more theobromine.) The amount of caffeine in the tea depends on how it’s made: Tea brewed from loose leaves almost always has more caffeine than tea made from tea bags or instant tea.
Caffeine and Fluoride Content of Brewed Teas
Tea Caffeine (mg/8-oz. cup) Fluoride (mg/8-oz. cup)
White 15 (na)
Green 20 0.3–0.4
Black 40 0.2–0.5
Oolong 30 0.1–0.2
Decaffeinated 2 (na)
Coffee (5-oz. cup) 40–170* (na)
Tea leaves are also rich in flavonoids, naturally occurring chemical compounds creditedwith tea’s ability to lower cholesterol, reduce the risk of some kinds of cancer, and protectthe teeth from cavity-causing bacteria. Fresh tea leaves are rich in flavonoids called catechins,but processing the leaves to make black and green teas releases enzymes that enableindividual catechins to join with others, forming new flavor and coloring agents calledpolyphenols (poly means many) that give flavor and color to black and green teas. The lengthof time tea leaves are left to dry before processing affects the rate at which their catechinsare converted to polyphenols. For example, white teas have fewer polyphenols than greenteas, which have fewer than oolong, which has fewer than black teas. As a result, nutritionresearchers at the Linus Pauling Institute at Oregon State University report that the catechincontent of white tea is three times that of green tea, with black tea a distant third. (Seebelow, Medical uses and/or benefits.)
Finally, tea leaves also contain antinutrient enzymes that can split the thiamin (vitaminB1) molecule so that it is no longer nutritionally useful. This is not generally considereda problem for healthy people who eat a balanced diet and consume normal amounts of tea,but it might trigger a thiamin deficiency if you drink a lot of tea and your diet is marginal inthiamin. The tannins in tea are also potential antinutrients that bind calcium and iron intoinsoluble compounds your body cannot absorb. According to the National Research Council of the National Academy of Sciences, an “inordinate” consumption of tea might substantiallyreduce the absorption of iron from foods. Tannins also interfere with the absorption of thiamin(vitamin B1) and vitamin B12. Finally, tea contains oxalates that can bind calcium andmight contribute to the formation of calcium-oxalate kidney stones in people predisposedto form stones.
Catechin Content of Various Teas
Tea/8-oz. serving Catechins
White tea 20.7 (estimate)*
Green tea 6.9 mg
Oolong (na)
Black tea 3.5 mg
*Based on the theory that white tea has three times as much as green tea.
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With milk. Milk protein (casein) binds and inactivates tannins.
Bland diet
Low-oxalate diet (for people who form calcium-oxalate kidney stones)
Look for: Tightly sealed packages. Tea loses flavor and freshness when it is exposed to air, moisture, or light.
Store tea in a cool, dark cabinet in an air- and moistureproof container, preferably a glass jar.
When brewing tea, always start with an absolutely clean glass, china, or enamel pot and, if possible, soft, mineral-free water. The tannins in tea leaves react with metals and minerals to create the compounds that make up the film sometimes seen floating on top of a cup of tea.
When tea leaves are immersed in water they begin to release flavoring agents plus bitter tannins, the astringent chemicals that coagulate proteins on the surface of the mucous membranes lining the mouth, making the tissues pucker. The best tea is brewed at the boiling point of water, a temperature that allows the tea leaves to release flavoring agents quickly without overloading the tea with bitter tannins.
If the brewing water is below the boiling point, the leaves will release their flavoring agents so slowly that by the time enough flavor molecules have been released into the brew, the ratio of bitter tannins will be so high that the tea tastes bitter. Brewing tea in water that is too hot also makes a bitter drink. At temperatures above boiling, the tannins are released so fast that they turn tea bitter in a minute or two.
You cannot judge the flavor of brewed tea by its color. Brewed black teas turn reddish brown, brewed green teas are almost colorless, and brewed white teas may be pinkish, but they all have distinctive flavors.
As a stimulant and mood elevator. Caffeine is a stimulant. It increases alertness and concentration,intensifies muscle responses, quickens heartbeat, and elevates mood. Its effectsderive from the fact that its molecular structure is similar to that of adenosine, a naturalchemical by-product of normal cell activity. Adenosine is a regular chemical that keeps nervecell activity within safe limits. When caffeine molecules hook up to sites in the brain whereadenosine molecules normally dock, nerve cells continue to fire indiscriminately, producingthe jangly feeling sometimes associated with drinking excess amounts of tea, coffee, andother caffeine products.
As a rule, it takes five to six hours to metabolize and excrete caffeine from the body.During that time, its effects may vary widely from person to person. Some find its stimulationpleasant, even relaxing; others experience restlessness, nervousness, hyperactivity,insomnia, flushing, and upset stomach after as little as one cup a day. It is possible to developa tolerance for caffeine, so people who drink tea every day are likely to find it less immediatelystimulating than those who drink it only once in a while.
NOTE: Theophylline, the primary stimulant in tea, relaxes the smooth muscles liningthe bronchi (the small passages that carry air into the lungs). As a drug, theophylline iseffective in relieving asthmatic spasms, but the relatively low concentrations in brewed teaare too small to produce therapeutic results.
Lower risk of some kinds of cancer. In 1991, a number of scientific teams at the Fourth ChemicalCongress of North America announced the identification of chemicals in teas that showpositive results in laboratory studies in which laboratory animals given green and blacktea have lower rates of skin tumors, esophageal tumors, gastrointestinal tract tumors, andtumors of the lung, liver and pancreas.
Eight years later, in January 1999, Purdue Universityresearchers released a study showing that EGCg, a compound in green tea, inhibits anenzyme required for cancer cell growth, killing cancer cells in laboratory dishes withoutharming healthy cells. The Purdue findings suggest that drinking four cups of green tea a daymay produce a lower overall risk of cancer. NOTE: People who drink tea when it is very hot(131°F to 153°F) have a higher risk of esophageal cancer than do people who drink tea at atemperature of 95°F to 117°F. The higher rate of cancer is almost certainly due to the tissuesbeing injured repeatedly by the extremely hot liquid.
Lower risk of cardiovascular disease (heart attack and stroke). Numerous studies have suggestedthat consuming moderate amounts of tea (five cups per day) reduces both overallmortality (death from all causes) and the risk of death from cardiovascular disease. There areseveral possible explanations for this finding. For example, in 2008, a report from INSERM,France’s national institute for medical research, found that women who drank three ormore cups of tea a day were 11 percent less likely than non–tea drinkers to have cholesterolplaques (deposits) inside their arteries.
In addition, drinking tea appears to increase the abilityof blood vessels to expand, an important factor in protecting against blood clots that mayblock the vessel, leading to a heart attack or stroke. In a clinical trial, one group of patientswith coronary artery disease and mildly elevated cholesterol levels were each given four tosix cups of black tea a day for at least four weeks, while a second group got either a beveragewith the equivalent amount of caffeine or plain hot water.
The blood vessels of patientswho drank tea daily dilated more effectively. Some researchers attribute this effect to thecatechins in tea.Lower risk of cardiovascular disease (heart attack and stroke). Numerous studies have suggestedthat consuming moderate amounts of tea (five cups per day) reduces both overallmortality (death from all causes) and the risk of death from cardiovascular disease. There areseveral possible explanations for this finding.
For example, in 2008, a report from INSERM,France’s national institute for medical research, found that women who drank three ormore cups of tea a day were 11 percent less likely than non–tea drinkers to have cholesterolplaques (deposits) inside their arteries. In addition, drinking tea appears to increase the abilityof blood vessels to expand, an important factor in protecting against blood clots that mayblock the vessel, leading to a heart attack or stroke. In a clinical trial, one group of patientswith coronary artery disease and mildly elevated cholesterol levels were each given four tosix cups of black tea a day for at least four weeks, while a second group got either a beveragewith the equivalent amount of caffeine or plain hot water.
The blood vessels of patientswho drank tea daily dilated more effectively. Some researchers attribute this effect to thecatechins in tea.
Many researchers do not consider these results conclusive either because many studiesshowing lower mortality were too small or because tea consumption in the general populationwas too low to allow reliable comparisons between tea drinkers and non–tea drinkers.As a result, while both black and green teas (and presumably white teas) appear to be protective,further research is needed to provide firm conclusions about tea and heart health.Lower risk of some forms of cancer.
Animal studies suggest that both green and black teasmay reduce the risk of cancers of the skin, lung, mouth, esophagus, stomach, colon, pancreas,bladder, and prostate, while white tea and green tea reduce the incidence of intestinalpolyps. Again, the effects are attributed to the flavonoids (catechins) in the teas. However,human studies have produced inconsistent results. For example, while some studies show adecreased risk of colon cancer among tea drinkers, others do not. In general, the assumptionis that further evidence is required before linking tea consumption and cancer prevention.
Lower risk of dental cavities. By observation, there appears to be a link between tea drinkingand a lower risk of dental decay. In addition, one study of more than 6,000 14-year oldchildren in the United Kingdom found that those who drank tea had significantly fewerdental caries than non–tea drinkers, regardless of whether they drank their tea plain or withsugar or milk and sugar. This result may be attributable to the natural presence of fluoridesin tea leaves.
Methylxanthine (theophylline and caffeine) effects. All methylxanthines are central-nervoussystemstimulants, vasoactive compounds that dilate the skeletal blood vessels and constrictblood vessels in the brain. Theophylline, which effectively relaxes the smooth muscles in thebronchi—the small passages that carry air into the lungs—is used as an asthma medication,but the relatively low concentrations of theophylline in brewed tea are too small to producetherapeutic effects.
Stimulation of the central nervous system. Taken in excessive amounts, caffeine and theophylline may cause rapid heartbeat, restlessness, sleeplessness, and/or depression in sensitive individuals. Since different people can tolerate different amounts of caffeine and theophylline without suffering ill effects, exactly which dose produces problems varies from person to person.
Constipation. The tannins in tea may be constipating.
Increased severity of premenstrual syndrome (PMS). Beta-estradiol and progesterone, two hormones that rise and fall during the monthly menstrual cycle, directly affect brain levels of adenosine (see above). Beta-estradiol (an estrogen), which rises just before ovulation, keeps adenosine from slowing down nerve cell activity, which may be why many women feel pleasantly energized at mid-cycle. Progesterone encourages adenosine; it’s a soothing hormone. That may be why many women feel tense and irritable when progesterone levels fall just before menstrual bleeding begins. Because caffeine alters adenosine activity in the brain, drinking tea may make beta-estradiol’s “highs” higher and progesterone’s “lows” lower. Because tea contains less caffeine than coffee, its effects would be much weaker.
Drugs that make it harder to metabolize caffeine. Some medical drugs slow the body’s metabolism of caffeine, thus increasing its stimulating effect. The list of such drugs includes cimetidine (Tagamet), disulfiram (Antabuse), estrogens, fluoroquinolone antibiotics (e.g., ciprofloxacin, enoxacin, norfloxacin), fluconazole (Diflucan), fluvoxamine (Luvox), mexiletine (Mexitil), riluzole (Rilutek), terbinafine (Lamisil), and verapamil (Calan). If you are taking one of these medicines, check with your doctor regarding your consumption of caffeinated beverages.
Drugs whose adverse effects increase due to consumption of large amounts of caffeine. This list includes such drugs as clozapine (Clozaril), ephedrine, epinephrine, metaproterenal (Alupent), monoamine oxidase inhibitors, phenylpropanolamine, and theophylline. In addition, suddenly decreasing your caffeine intake may increase blood levels of lithium, a drug used to control mood swings. If you are taking one of these medicines, check with your doctor regarding your consumption of caffeinated beverages.
Allopurinol. Tea and other beverages containing the methylxanthine stimulants (caffeine, theophylline, and theobromine) reduce the effectiveness of the xanthine inhibitor, antigout drug allopurinol.
Antibiotics. Drinking tea increases stomach acidity, which reduces the absorption of the antibiotics ampicillin, erythromycin, griseofulvin, penicillin, and tetracycline.
Anticoagulants. Green tea is high in vitamin K, the blood-clotting vitamin produced naturally by bacteria in our intestines. Using foods rich in vitamin K while you are taking an anticoagulant (warfarin, Coumadin, Panwarfin) may reduce the effectiveness of the anticoagulant, so larger doses are required.
Antiulcer medication. Drinking tea makes the stomach more acid and may reduce the effectiveness of normal doses of cimetidine and other antiulcer medication.
Iron supplements. Caffeine and tannic acid bind with iron to form insoluble compounds your body cannot absorb. Ideally, iron supplements and tea should be taken at least two hours apart.
Monoamine oxidase (MAO) inhibitors. Monoamine oxidase inhibitors are drugs used to treat depression. They inactivate naturally occurring enzymes in your body that metabolize tyramine, a substance found in many fermented or aged foods. Tyramine constricts blood vessels and increases blood pressure. Caffeine has some similarity to tyramine; if you consume excessive amounts of a caffeinated beverage such as tea while you are taking an MAO inhibitor, the result may be a hypertensive crisis.
Nonprescription drugs containing caffeine. The caffeine in brewed tea may add to the stimulant effects of the caffeine in some cold remedies, diuretics, pain relievers, stimulants, and weight-control products. Some over-the-counter cold pills contain 30 mg caffeine, some pain relievers 130 mg, and some weight-control products as much as 280 mg caffeine. There are 21 to 47 mg caffeine in a five-ounce cup of brewed tea.
Sedatives. The caffeine in tea may counteract the drowsiness caused by sedative drugs.
Theophylline. The theophylline and caffeine in brewed tea may intensify the effects and/or increase the risk of side effects from this antiasthmatic drug.
