The story goes that the Emperor Shen Nong was boiling a pot of water in 2737 B.C., when a gust of wind blew a tea leaf into the water. The emperor was pleased with both the taste and effects of the new beverage. He declared that “tea can provide vigor of body, contentment of mind and determination of purpose.” Chen Zang, a famous pharmacist of the Tang Dynasty noted, “Every medicine is the only medicine for a specific disease, but tea is the medicine for all diseases.” Another pharmacist, Want Ang, proved himself prescient when he said that drinking tea for a long time can eliminate fat.
Today tea is the second most popular beverage in the world, trailing only water. The three main types of tea are black, green and oolong. All are derived from the plant Camellia sinensis, specifically its leaves. The main differences between the teas lies in the degree of fermentation, with black tea being the most fermented and green tea the least. Green tea is produced from steaming fresh leaves at high temperatures, which inactivates oxidizing enzymes but leaves intact the polyphenol antioxidants that are its primary active ingredients.
Black tea accounts for 78 percent of worldwide tea consumption, green tea for 20 percent and oolong less than 2 percent. Green and oolong teas are drunk mainly in Asia, while black tea is more popular in Europe and the United States. Oolong is considered an intermediate between black and green tea, in that it’s partially fermented. Another variety, white tea, contains both leaves and tea buds, which impart a pale color.
The polyphenols in tea are known chemically as flavonols or catechins, the latter of which make up 30 to 40 percent of the dry weight of green tea. The major and most active catechin in green tea is epigallocatechin gallate, or EGCG, 65 percent of total catechin content. A cup of green tea contains 100 to 200 milligrams of EGCG.1 Other catechins found in green tea are also in chocolate, black grapes, red wine and apples. Black tea, because of the greater fermentation process, has the lowest catechin content, though it has some unique ingredients that also impart health benefits, as we’ll see.
Though tea is primarily categorized as an antioxidant, its effects extend well beyond that, with a versatility that few other supplements or foods can match. Green tea offers cardiovascular protection, cancer preventive effects, brain protection and fat-loss properties. How? Read on.
There’s some controversy about the extent to which the human body can absorb flavonols. While in vitro, or test-tube, studies show a number of beneficial effects, they don’t seem to occur in the body. Catechin uptake is very limited—0.2 to 2 percent of the amount taken in. The maximum absorption in the blood is reached 1.4 to 2.4 hours following intake, with EGCG lasting the longest, an average of five hours.2
The kind of food that you wash down with tea affects polyphenol absorption. Tea polyphenols have an affinity for an amino acid called proline, which is contained in casein. In some countries, such as England, milk is commonly added to tea. In the case of black tea, this doesn’t make much difference, since black tea is relatively low in active polyphenols. Some studies show that the casein in milk can completely negate the activity of the polyphenols by binding to them. Other studies show that this doesn’t occur.3 Green tea polyphenols form strong complexes with iron, which some studies show blunts their activity. One study found that eating meat, which is rich in iron, along with casein decreased green tea’s antioxidant activity.4 The same study demonstrated that, at least in test tubes, vitamin C enhanced the tea’s antioxidant properties.
Another study, however, which used 30 human female subjects who had low iron stores, revealed that tea did not affect the absorption of non-heme iron, a type of iron found in plant and animal foods.5 Still, tea’s binding effect on iron applies only to non-heme iron and would not work with heme iron, the type of iron found in red meat. In any event, taking vitamin C, which boosts iron uptake, can help overcome any absorption impairment. In regard to other minerals, tea polyphenols interfere with the uptake of sodium and aluminum—a good thing—but not of manganese, calcium or magnesium.6
Tea Against Cancer A number of studies show that tea polyphenols help inhibit tumor formation and growth. The diseases affected are leukemia, as well as cancers of the prostate, breast, esophagus, stomach, pancreas, colon, lung, skin, liver, bladder and ovaries.
According to scientists who study the mechanisms of cancer, the ideal qualities of a cancer-preventive substance should include the following:7
• Known mechanism
• Human acceptance
• Little or no toxicity
• High effectiveness
• Can be taken orally
• Low cost
• Stable active form
• Proven effective in the laboratory
All of those factors apply to tea, yet proof of its strength against cancer is not definitive for a number of reasons. The amount of tea that protects animals from cancer is far more than most humans drink. Some studies estimate that the minimum you need is 10 cups a day. The mechanisms through which tea blocks tumors in animals may not be applicable to humans. Many known carcinogens in animals don’t affect humans, and vice versa. ALL Even so, tea is a plausible anticancer agent. It interferes with the pathways that tumors exploit to grow. Tea polyphenols can block cell proliferation, a hallmark of cancer, and may also help active cancer cells self-destruct.8
A study involving mice, which develop prostate cancer more or less the way humans do, found that giving them a dose of polyphenols equilvalent to six cups of green tea inhibited the development and spread of prostate cancer.9 The levels of insulinlike growth factor-1 and insulinlike growth factor-binding protein-3 were inhibited by 70 to 83 percent. That’s significant because IGF-1 stimulates tumor proliferation by way of cell proliferation. The study also showed that green tea inhibited other markers of tumor spread: vascular endothelial growth factor, urokinase plasminogen activator and matrix metalloproteinase 2 and 9.
Tumors spread in the body via angiogenesis, the name given to the formation of new blood vessels. To grow, tumors require a rich blood supply, and if something interferes with the growth of new blood vessels, the tumor will shrink and die. That’s a major focus of cancer research, and many scientists are investigating experimental drugs that may inhibit it—important because 90 percent of all cancers are curable before they begin to spread.
A study reported in the journal Nature in 1999 by researchers from the Karolinska Instutute in Stockholm, Sweden, focused on one group of four mice that got tea as their sole source of fluid and another four mice that got plain water only. The authors used gene therapy to stimulate the abnormal growth of blood vessels in the eyes of the rodents. The ones that drank only the green tea had 35 to 70 percent less blood vessel growth than the water-drinking mice.
One reason that testosterone is thought to stimulate prostate cancer is that it increases the activity of ornithine decarboxylase, an enzyme in the prostate gland. ODC is known to be overabundant in prostate tumors. In one study mice were treated with testosterone and then given ODC in their drinking water, which led to a significant increase in ODC activity in the mice.10 Then the mice were given green tea, and ODC activity decreased by 40 percent. The study suggests that green tea may eliminate the impact of testosterone on prostate cancer. Although studies in the United States show no relationship between the intake of tea and breast cancer, a Japanese study turned up an inverse relationship between breast cancer and tea intake after seven years. That may be due to green tea’s interference with estrogen metabolism, which is known to stimulate breast cancer. It’s noteworthy for bodybuilders who are concerned about estrogen.
An alarming report a few years ago linked esophageal cancer to tea drinking. An analysis of 28 human studies of green tea and cancer reported a link between decreased cancer rates and green tea intake in 17 of the studies. Seven showed a higher rate of cancer among green tea drinkers, while another five linked esophageal cancer to drinking particularly hot tea. Scalding tea is known to damage cells in the esophagus, which could lead to cancer. The solution is simple: Don’t drink tea so hot that it burns your throat.
Smoking is the greatest risk factor for lung cancer. One experiment found that drinking two cups of black tea a day reduced the incidence of lung cancer by 66 percent in 855 male smokers in Uruguay. Another study discovered that regular intake of green tea may offer some antioxidant protection against the carcinogens in tobacco smoke by preventing the DNA damage that sets in motion the development of precancerous cell mutations.11 Green tea boosted the self-destruction of cancer cells and prevented the miscoding of DNA through gene regulation, and it activated the liver enzymes that can spur the breakdown and excretion of tobacco-smoke carcinogens.
Purdue University researchers suggest that green tea may block cancer by interacting with quinol oxidase, or NOX, an enzyme found on the surface of cancer cells that the cells use to grow and spread. Normal cells also use NOX for growth phases, when it’s stimulated by growth hormone. Cancer cells can produce the enzyme without the hormone, and drugs that block the enzyme inhibit tumor growth. Studies of cell cultures found that while black tea inhibited the activity of the enzyme, green tea was 10 to 100 times more potent. The Purdue researchers found that drinking four or more cups a day was enough to diffuse the cancer-causing effects of NOX without adversely affecting normal cell growth.
Spanish and British researchers came up with another theory of how green tea inhibits cancer. They found that EGCG binds to dihydrofolate reductase, an enzyme that helps produce DNA by activating folic acid in cells. The chemo drug methotrexate also binds to and inhibits DHFR, but ECGC has less chance of damaging healthy cells in the process. Still, since DHFR is also required to convert folic acid into its active form in the body, this raises the question of whether green tea may interfere with folic acid uptake and, paradoxically, encourage cancer. A recent test-tube study found that EGCG can indeed interfere with the uptake of folic acid in the intestine by interfering with DHFR.12
Overcooking meat is linked to colon cancer because well-done meat contains carcinogens called heterocyclic mutagens. One rat study found that drinking black and green teas inhibited the formation of those carcinogens in cooked meat and fish. A 5 percent brew of green tea decreased the carcinogen activity by more than 90 percent, chiefly because the tea stimulated the detoxification properties of liver enzymes.13
The effect of green tea on cancer is best summed up by a recent review: “Our conclusion is that daily large consumption of green tea, specifically 10 cups and over a day, will add a little lifetime to those who already lived the average life span of about 80 years, but it will help to prolong the lifetime of those aged below the average life span by avoiding premature death, specifically that caused by cancer.”14
Next time we’ll cover tea’s cardiovascular- and skin-strengthening effects, as well as how it can reduce bodyfat and improve brain function. References
1 Zaveri, N. (2005). Green tea and its polyphenolic catechins: Medicinal uses in cancer and noncancer applications. Life Sci. 78(18):2073-80.
2 Yang, C.S., et al. (1999). Inhibition of carcinogenesis by tea: Bioavailability of tea polyphenols and mechanisms of actions. Proc Exper Biol Med. 220:213-217.
3 Leenen, R., et al. (2000). A single dose of tea
with or witout milk increases plasma antioxidant activity in humans. Eur J Clin Nutr. 54:87-92.
4 Alexandropoulou, I., et al. (2006). Effects of iron, ascorbate, meat and casein on the antioxidant capacity of green tea under conditions of in vitro digestion. Food Chem. 94:359-65.
5 Ullman, U., et al. (2005). Epigallocatechin gallate (ECGC) does not impair non-heme iron absorption in man. Phytomedicine. 12:410-15.
6 Bravo, L. (1998). Polyphenols: Chemistry, dietary sources, metabolism, and nutritional significance. Nutr Rev. 56:317-35.
7 Mukhtar, H., et al. (1999). Mechanism of cancer chemopreventive activity of green tea. Pr Exp Biol Med. 220:234-238.
8 Yang, C.S., et al. (2000). Tea and tea polyphenols in cancer prevention. J Nutr. 130:472S-478S.
9 Vaqar, M.A., et al. (2004). Oral consumption of green tea polyphenols inhibits insulinlike growth factor-1 induced signaling in an autochthonous mouse model of prostate cancer. Cancer Res. 64:8715-32.
10 Gupta, S., et al. (1999). Prostate cancer chemoprevention by green tea: In vitro and in vivo inhibition of testosterone-mediated induction of ornithine decarboxylase. Cancer Res. 59:2115-20.
11 Llang, W., et al. (2007). Does the consumption of green tea reduce the risk of lung cancer among smokers? ECAM. 4:17-22.
12 Alemdaroglu, N., et al. (2007). Inhibition of folic acid uptake by catechins and tea extracts in caco-2 cells. Planta Med. 73:27-32.
13 Dashwood, R.H., et al. (1999). Cancer chemopreventive mechanisms of tea against heterocyclic amine mutagens from cooked meat. Proc Soc Exp Biol Med. 220:239-43. 14 Nakachi, K., et al. (2003). Can teatime increase one’s lifetime? Aging Res Rev. 2:1-10. IM