It is estimated that the average world-wide consumption of tea (Camellia sinensis) is slightly in excess of 100 ml per day, but it can range up to 20 cups per day (Graham, 1992). Tea was the major source of flavonoids in a Dutch study which correlated lower risks for cardiovascular disease to higher intakes of flavonoids (Hertog et al. 1993). Green and black tea leaves contain up to 35% polyphenols by dry weight, whose nature is dependent on the tea variety and especially the processing. In general, green tea is rich in flavonols, (mainly catechin, epicatechin, and epigallocatechin), flavandiols, and simple phenolic acids. Black tea is formed by fermentation of green tea, and this process tends to polymerize (i.e. condense, as in "condensed tannins") the polyphenols. Black tea is rich in theaflavins and thearubigens, which are oxidized and polymerized derivatives of the catechins. A number of minor volatile compounds are also formed during fermentation, and these produce the myriad of flavors and aromas in black tea botanical varieties and commercial blends. The theaflavins and thearubigens give black tea its characteristic astringency and reddish color. The astringency of black tea is often moderated by the addition of sugar and/or milk to tea. Oolong tea is semi-fermented and has characteristics and chemistry intermediate between black and green (Gutman and Ryu, 1996; Serafini et al. 1996). Although most herbal beverage-type teas have not been studied to anywhere near the extent that Camellia sinensis has, many favorite herb teas are fairly similar to green tea in that they contain flavonoids and phenolic acids. Examples of such favorite tea herbs are chamomile, raspberry leaf, peppermint, lemon balm, hibiscus, rosemary, rosehips, meadowsweet, and many popular herbal blends on the market.
Tea polyphenols are known to be antioxidant, anti-carcinogenic, anti-mutagenic, and may protect against many diseases. Recent research is reviewed in detail by Graham (1992), Willson and Clifford (1992) and Gutman and Ryu (1996). Higher levels of tea consumption are linked to lower risks for esophageal, gastric, pancreatic, and colon cancer. Tea consumption also appears to lower platelet aggregation, cholesterol levels, blood pressure, and incidence of dental caries (cavities). In vitro tests have shown that tea polyphenols can inhibit the growth of bacteria, viruses, and protozoa, but there are no in vivo studies indicating that tea consumption prevents or cures such infections.
A cup of tea is something that many women cherish, and make a part of their daily routine. Oriental cultures in particular celebrate tea with ceremonies, rituals, and special teapots and tea cups. Different teas are used for different times of the year, occasions, and physical ailments or conditions. Tea consumption is thought to promote longevity, tranquillity, and happiness. There may be some truth in this-the ceremony associated with tea as well as the tea itself may relieve tension and produce a feeling of psychological well-being (Willson and Clifford, 1992; Sadakata et al. 1992).
Tea seems like an ideal beverage for women, since it's full of flavor, yet can be free of calories and/or caffeine if one chooses. However, for many years doctors and nutritionists have warned women that tea drinking can be a major cause of anemia. The reason for this is that the tea polyphenols, commonly known as "tannins" have a great affinity for iron, and bind to iron ions in the digestive tract. The bound iron cannot be absorbed, so no matter the intake, anemia can occur. The solution to this problem is fairly simple, though. If tea is consumed with milk, the polyphenols complex with the milk proteins, and thus leave the iron more or less free to be absorbed. This complexing with milk may be familiar to some of you: sometimes milk will curdle when added to strong tea. This does not necessarily mean that the milk has "gone off", only that your particular cup of tea had a strong affinity for milk protein, or is very strong. You may find that skim milk curdles more readily than whole milk or half-and-half, due to skim milk's higher protein content per serving. The move toward stronger teas with more "kick" and less fat has actually increased this little nuisance.
Now that we have this problem sewn up, the progress of science will do what it often does best, and throw a monkey wrench into our plans. In a recent in vitro and controlled in vivo human study, Serafini et al. (1996) confirmed the antioxidant effect of commercial Chinese green and Earl Grey black tea with and without milk. Teas were prepared with boiling water and were typical commercial products. In vitro, both green and black teas strongly inhibited peroxidation, and green tea was 6 times more protective than black tea. The addition of whole milk had no effect on the system.
In vivo, two groups of five subjects each were given 300 ml unsweetened green or black tea after an overnight fast. On a separate day, the same subjects were given tea plus whole milk in a 4 to 1 ratio. Five control subjects were given water. Blood samples were taken 30, 50, and 80 minutes after tea ingestion. Green tea inhibited peroxidation of the blood samples over baseline by 40%, with the peak inhibition occurring at 30 minutes. Black tea inhibited peroxidation of the blood samples by 48%, with the peak occurring at 50 minutes. There were no significant changes above baseline in the control group. The addition of milk totally or near totally inhibited the antioxidant effect of both teas. This can be due to the complexing of the polyphenols with milk proteins, and to slight increases in the gastric pH (i.e. less acidity in the stomach) caused by the introduction of milk, which may act to decrease the absorption of polyphenols. (Simple phenolics can be absorbed directly through the stomach lining). The authors concluded that the polymeric polyphenols in black tea are likely to be broken down fairly rapidly, probably in the stomach (especially by the stomach acid) and in the upper intestines. In addition, in vitro tests are not predictive of in vivo results. Either green or black tea can provide significant antioxidant protection, but not when consumed with milk.
If you favor tea without milk and would rather protect yourself from cancer and cavities than anemia, it is of course possible to consume tea away from meals that contain a lot of iron. This means that if you have meat or fish for dinner, you may want to skip iced tea or hot tea for several hours before and after the meal. Keep in mind when you do this that you may not yet be free of monkey wrenches. Binding of iron, zinc, and sometimes other essential trace elements is not restricted to tea, but is widespread throughout the plant kingdom. Spinach, dandelion greens, and nettles are widely described as "good sources of iron", but they, in fact, lead to iron depletion. These and other dark leafy green plants do contain iron, but the polyphenolics, oxalic acid, and phytates that they contain bind up iron in the digestive tract, rendering it unabsorbable. What's more, spinach and similar greens were shown to actually grab some of the iron provided by other foods in mixed meals (Brune et al. 1989; Tunatawiroon et al. 1991; Dr. Rufus Chaney USDA Beltsville, personal communication)! Oregano is exceptionally good at binding up iron: 1.5 g added to a roll made with iron-fortified wheat flour inhibited iron absorption by 69% as compared to a similar plain roll (Brune et al., 1989; galloyl phenolics were though to be responsible). Duke (1995) found that oregano had the highest antioxidant potential of selected edible/medicinal mints, and this is likely not coincidental. In general, it may be that the better the polyphenolic antioxidant profile, the better iron is complexed, so as usual natural products have their good and bad points depending on how you look at it. Typically oregano is not consumed in great quantity; however excessive use of herbal teas with oregano and related plants from the mint family will likely pose the same type of risk for anemia that C. sinensis teas do.
Soy foods, other legumes, whole grains, and brans are notorious sources of phytates and other nutrient-absorption inhibitors (Bressani et al. 1983; Prasad 1993; Fallon and Enig 1995) and this is one of the drawbacks of high fiber, low fat, and mainly vegetarian diets. The actual intake of iron and zinc may be more than adequate, yet vegetarian women of childbearing age are often still anemic, and may be severely zinc deficient. Similarly, children raised in affluent households where the families practice macrobiotic diets (very restrictive, pure vegan) have been shown consistently to have severe nutritional deficiencies, lower birth weight, subsequent infant/childhood growth retardation, and slower development of gross motor, speech, and language skills than children raised on omnivorous diets (Dagnelie et al. 1994). The most common deficiencies were vitamin B12, vitamin D, calcium, iron, zinc, essential fatty acids, and protein. Believe it or not, many of these children suffer from rickets! We can only imagine the risks engendered for osteoporosis and arthritis later in life.
Given all these concerns, the mantra of the nutritional supplement skeptic "you can get everything you need from a balanced diet" is just not practical. The ultimate solution for women who want to protect both themselves and their families from anemia and chronic diseases, (while also following the diet of their choice, be it good or bad . . .) is to take supplements which ensure that they get adequate trace elements, vitamins, and yes-even tea polyphenols. It might be easier to take an herbal tea or "botanical antioxidant" supplement in between meals than worry about how and when you drink tea. Similarly, mineral supplements can be taken alone if necessary, or with meals or snacks that contain little or no tea, soy, or whole grains.
Graham, H.N. (1992). Green tea composition, consumption, and polyphenol chemistry. Prev Med 21: 334-350.
Hertog, MG., Hollman, PCH. (1995). Potential health effects of the dietary flavonol quercetin. Eur J Clin Nutr 50: 63-71.
Gutman, RL., Ryu, B.H. (1996). Rediscovering tea. Herbalgram 37: 33-48.
Serafini, M., Ghiselli, A., Ferro-Luzzi, A. (1996). In vivo antioxidant effect of green and black tea in man. Eur J Clin Nutr 50: 28-32.
Willson, KC., Clifford, MN. eds. (1992). Tea: Cultivation to Consumption. Chapman and Hall, New York.
Sadakata, S., Fukao, A., Hisamichi, S. (1992). Mortality among female practitioners of the Chanyou (Japanese Òtea ceremonyÓ). Tohoku J Exp Med 166: 475-477.
Brune, M., Rossander, L., Hallberg, L. (1989). Iron absorption and phenolic compounds: importance of different phenolic structures. Eur J Clin Nutr 43: 517-558.
Tuntawiroon, M., Sritongkul, N., Brune, M. et al. (1991). Dose-dependent inhibitory effect of phenolic compounds in foods on nonhene-iron absorption in men. Am J Clin Nutr 53: 554-557.
Duke, J.A. (1995). Synergy in the garden. Organic Gardening July/Aug, 41-46.
Bressani, R., Elias, LG., Wolzac, A. et al. (1983). Tannin in common beans: methods of analysis and effects on protein quality. J Food Sci 48: 1000-1001.
Prasad, A.S. (1993). Essential and Toxic Trace Elements in Human Health and Disease: An Update: Wiley-Liss, New York, 1993.
Fallon, SW, Enig, MG. (1995), Soy products for dairy products? Not so fast. Health Freedom News, September 12-20.
Dagnellie, PC., van Dusseldorp, M., van Staveren, WA., Hautvast, JGAJ. Effects of macrobiotic diets on linear growth in infants and children until 10 years of age. Eur J Clin Nutr 48: S103-S112.