Read 2365125 times
Connect me to:
Green Tea: Health Perspectives
Summer Volume: 2002 Issue: 9(2) page(s): 19 and 23
Eastern cultures have considered tea a healthy drink for four or more thousand years, the Chinese using it for medicinal purposes since these early times. Tea was known as a treatment for everything from sore throats to unsettled stomachs. It is still used for these purposes. Current research about the positive effects of green tea are of interest on every continent, however, not everyone agrees every medical use ascribed for this beverage. As a matter of fact, there is considerable controversy among researchers in the western world.
One such, but a minor controversy, is in using the very term 'tea.' Some people say tea and mean just the leaves, while others refer to the beverage made by infusing them in hot or boiling water. Another controversy is in which tea you mean when you say the word 'tea.' Most people do not differentiate between green, oolong, or black tea, though they should. They do not even know that every leaf or infusion is from the leaves of the very same plant, Camellia sinensis. In general, people lump all kinds of tea together because they know so little about this beverage. This is surprising as in the United States at least, people are drinking more than three billion gallons of this beverage a year.
What sets tea apart into its different color groups is the way it is processed. Usually, freshly harvested leaves are dried a mite then rapidly pan-fired, 'fermented' which more correctly is called 'oxidized,' or they are steamed to inactivate enzymatic reactions and prevent further oxidation. The leaves are then rolled to reduce moisture content and finally they are reheated, often in large mechanical dryers. To produce black and oolong teas, leaves are what is called 'withered' to allow for further oxidization. Oolong tea is green tea leaves further processed and on the way toward becoming black leaves. Just before they are referred to as black tea leaves is an intermediary name, Formosa Oolong. This language of calling tea by the color of the leaf is common in the western world. In China, tea is classified by the color of the infusion and so called by the liquid seen in the cup. There, the groupings are: white, yellow, green, and red.
Considerable research has been done on all kinds of tea, no matter the leaf or the liquid’s color. Some have concluded that one or another leaf or brew or the components of either or both has beneficial effects. Research about green tea reports benefits from natural compounds in it known as polyphenols, flavonols, and catechins. In actuality, technically these are one and the same. For those reading this article that consider themselves techno-buffs, be advised that the major catechin in green tea is epigallocatechin-3-gallate (EGCG). There are other compounds, and many of them have been studied extensively, as well, with positive and less than positive results about each of them.
Current research is pointing toward tea having anticarcinogenic, antimutagenic and antioxidant properties. A considerable number of studies done with green teas shows some chemotherapeutic effects, particularly for colorectal cancer. Tea’s biologic activity was found in rectal mucosa where it showed inhibition of a compound called prostaglandin E2 (PGE2). This particular compound has been linked to lowering cancer risk in other studies. In one of them, seventy-one percent of the subjects showed a fifty percent inhibition of PGE2 four hours after they ingest green tea infusions. Scientists are also investigating green tea’s effects on other types of human carcinomas. They are learning that the green tea polyphenols cause early cell death when consumed even in low doses. Their research shows that tea impacts cancerous cells and has less on an effect on healthy normal cells.
Green tea, more so than black tea, has been shown to inhibit the activity of quinol oxidase (NOX), an enzyme found on the surface of cancerous cells. Other researchers in Japan, where there is a high incidence of gastric cancer, found no association between the consumption of green tea and the risk of gastric cancer. Surprisingly, there was a small but not a significant increase in the risk of gastric cancer in subjects who drank more than five cups per day compared to those who drank less than two cups each day.
Studies done on green tea’s impact on cardiovascular disease show that oxidation of low-density lipoproteins (LDL’s) plays an important role in the development of atherosclerosis. One study shows that green and black teas increase antioxidant activity and that there is greater protection of LDL’s after ingesting black tea than green tea. In yet another study, all the catechins in an oil-in-water tea emulsion promoted oxidation equally. Because they did, green tea may be useful as a food preservative.
Green tea’s anti-inflammatory effects impacting immunity have also been studied. Here, they find that green tea reduces arthritis in laboratory mice; and the rodents that consume it have a lower incidence of this inflammatory disease. Furthermore, the onset of the symptoms and their severity is delayed in the mice who drink green tea infusions compared to those that do not.
Not all tea drinking has positive effects. Studies have shown that hot tea increases the risk of esophageal cancer. Several such studies show that there can be a two to three fold increased risk of this type of cancer among those who ingest hot tea. Researchers are not clear about whether this effect is due to the tea polyphenols or to physical damage of the esophageal cells due to drinking a hot liquid.
One benefit of green tea consumption points to strengthening tooth enamel and thereby preventing dental caries. That research believes that this is due to the fluoride content of the tea and its antibacterial properties. On the risk side, studies show that the levels of fluoride in tea can exceed recommended intake amounts. Therefore, tea could be harmful if consumed in large amounts. The reasoning here is that fluoride is used as a treatment for hyperthyroidism, making it a thyroid gland poison. Fluoride has also been linked to numerous central nervous system diseases. Another negative effect of drinking tea is in terms of the caffeine content. Excessive caffeine intake can be addictive. It also can cause nervousness, headaches, agitation and insomnia.
People need to know that every eight ounces of a green tea beverage contain thirty to sixty milligrams of caffeine and equivalent stimulants, the actual amount has to do with whether the leaf is whole or broken, how long it is brewed, and how green or light the leaf and/or the infusion actually is. Oolong teas have more stimulant than do green teas, and black teas have even more caffeine still. Coffee has more caffeine than does tea; there are more than a hundred milligrams of this stimulant in every eight ounces consumed. Just like tea, the darker the roast, the finer the grind, and the longer it is brewed impact the amount of caffeine.
It is nice to end on a positive note. That said, are you aware that green tea is an age-old Chinese dieter’s remedy? A recent study confirms this thinking. Those who drink several cups of green tea daily use up about seventy calories more every day than those who do not. That is seven pounds of weight lost in a year. Why, because the catechin antioxidants in the tea are enhance the metabolism of calories.
Certainly, many beneficial effects of green tea have been demonstrated; however, benefits are shown only in some studies and not in all of them. Dietary practices, age, and sex may influence these differences. Thus, there is need for more human clinical trials and more long-term studies to help determine the optimal amount of green tea to consume in a day. Additional studies are needed for black and oolong teas, too, to advise other health benefits of tea. While large quantities of tea may have negative effects due to fluoride and caffeine content, it does seems reasonable, while waiting for their results, to recommend green tea as a health drink with the following caveats: Do not consume tea in excessive amounts and do not consume it at very high temperatures.
While the jury is out researching and debating the various values in tea, keep one last thing in mind: Tea drinking is participating in a relaxing activity and that is important because stress negatively impacts health. Therefore, do be sure to enjoy a fine cup of tea.
Elaina Muñoz-Hamill is a registered dietitian currently employed as the assistant director at a major Catholic medical center/hospital in New York City. She will soon complete her Master’s Degree in Nutrition Education at Queens College.