Teas and their known health benefits

•  Preventing/treating cancer. link
  
• Treating multiple sclerosis. link
  
• Preventing the degradation of cell membranes by neutralizing the spread of free radicals. link
  
• Reducing the negative effects of LDL cholesterol (bad cholesterol) by lowering levels of triglycerides and increasing the production of HDL cholesterol good cholesterol.
• Increasing fat oxidation (helps the body use fat as an energy source) and raising metabolism. link
  
• Joy Bauer, a New York City nutritionist, says [the catechins in green tea] increase levels of the metabolism speeding brain chemical norepinephrine.
  
• Drinking green tea mixed with honey can oftentimes have a soothing effect on a sore throat.
  
  

Tea has a long history of medical benefits, first noticed in ancient times, and continuing to be discovered today.

Currently over 450 chemical substances have been discovered in tea, some of which are microelements capable of supplementing nutrient substances needed by the body and some other microelements can prevent or cure disease.

Green tea is a nutritious drink full of vitamins.  It contains a kind of hydroxybenzene, which can restrain cancer cells and thus help to prevent or resist cancer.

Oolong tea can control the absorption of dextrose by the human body, and is traditionally used in Chinese society as a weight loss aid.

Black (red) tea is mild, which is good for phlegm reducing, digesting and increasing appetite, especially good for people with a weak spleen.

Pu'er tea has been shown to help prevent cardiovascular diseases and has been known in China as the, "Tea of Longevity."

Tea containscatechins, a type of antioxidant. In a fresh tea leaf, catechins can be up to 30% of the dry weight. Catechins are highest in concentration in white and green teas, while black tea has substantially less due to its oxidative preparation.

Tea contains theanine, and the stimulant caffeine at about 3% of its dry weight, translating to between 30mg and 90mg per 8oz (or 0.25 L) cup depending on type and brand and brewing method.

Tea also contains small amounts of theobromine, theophylline and fluoride, with certain types of brick tea made from old leaves and stems having the highest levels. Regular drinking of tea can prevent dental cavity to some extent. However, excessive consumption of tea (brick tea in particular) has led to cases of fluorosis. In addition to these properties, tea leaves are also known to help prevent radiation.

A 2006 study published in the September 13 issue of the Journal of the American Medical Association concluded "Green tea consumption is associated with reduced mortality due to all causes and due to cardiovascular disease but not with reduced mortality due to cancer." The study, conducted by the Tohoku University School of Public Policy in Japan, followed 40,530 Japanese adults, ages 40-79, with no history of stroke, coronary heart disease, or cancer at baseline beginning in 1994. The study followed all participants for up to 11 years for death from all causes and for up to 7 years for death from a specific cause. Participants who consumed 5 or more cups of tea per day had a 16 percent lower risk of all-cause mortality and a 26 percent lower risk of cardiovascular disease than participants who consumed less than one cup of tea per day. The study also states, "If green tea does protect humans against CVD or cancer, it is expected that consumption of this beverage would substantially contribute to the prolonging of life expectancy, given that CVD and cancer are the two leading causes of death worldwide."

Oncologist Dr. Mitchell Gaynor indicates in his cancer prevention book [Cite] that "Green tea catechins are among the phenolic compounds known to suppress the formation of tetracycline amines and antihistamines, known to be potent carcinogens. Many other carcinogens are likewise rendered less harmful thanks to the action of green tea polyphenols on inducing enzymes that detoxify various undesirable compounds, inhibiting those enzymes that would make certain carcinogens bioactive."

A study published in the February 2006 edition of the American Journal of Clinical Nutrition concluded "A higher consumption of green tea is associated with a lower prevalence of cognitive impairment in humans."  In May 2006, researchers at Yale University School of Medicine weighed in on the issue with a review article that looked at more than 100 studies on the health benefits of green tea. They pointed to what they called an "Asian paradox," which refers to lower rates of heart disease and cancer in Asia despite high rates of cigarette smoking. They theorized that the 1.2 liters of green tea that is consumed by many Asians each day provides high levels of polyphenols and other antioxidants. These compounds may work in several ways to improve cardiovascular health, including preventing blood platelets from sticking together (This anticoagulant effect is the reason doctors warn surgical patients to avoid green tea prior to procedures that rely on a patient's clotting ability) and improving cholesterol levels, said the researchers, whose study appeared in the May issue of the Journal of the American College of Surgeons. Specifically, green tea may prevent the oxidation of LDL cholesterol (the "bad" type), which, in turn, can reduce the buildup of plaque in arteries, the researchers wrote.

A study published in the August 22, 2006 edition of Biological Psychology looked at the modification of the stress response via L-Theanine, a chemical found in green tea. It "suggested that the oral intake of L-Theanine could cause anti-stress effects via the inhibition of cortical neuron excitation."

In a double-blind, randomized, placebo-controlled trial done by Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, 240 adults were given either theaflavin-enriched green tea extract in form of 375mg capsule daily or a placebo. After 12 weeks, patients in the tea extract group had significantly less low-density lipoprotein cholesterol (LDL-C) and total cholesterol (16.4% and 11.3% lower than baseline, p<0.01) than the placebo group. The author concluded that theaflavin-enriched green tea extract can be used together with other dietary approaches to reduce LDL-C.

A study published in the January, 2005 edition of the American Journal of Clinical Nutrition concluded "Daily consumption of tea containing 690 mg catechins for 12 wk reduced body fat, which suggests that the ingestion of catechins might be useful in the prevention and improvement of lifestyle-related diseases, mainly obesity."

Antioxidants in green tea may prevent and reduce the severity of rheumatoid arthritis, according to a Case Western Reserve University School of Medicine study published in the April 13 2005 issue of the Proceedings of the National Academy of Sciences. The study examined the effects of green tea polyphenols on collagen-induced arthritis in mice, which is similar to rheumatoid arthritis in humans. In each of three different study groups, the mice given the green tea polyphenols were significantly less likely to develop arthritis. Of the 18 mice that received the green tea, only eight (44 percent) developed arthritis. Among the 18 mice that did not receive the green tea, all but one (94 percent) developed arthritis. In addition, researchers noted that the eight arthritic mice that received the green tea polyphenols developed less severe forms of arthritis.

A German study found that an extract of green tea and hot water (filtered), applied externally to the skin for 10 minutes, three times a day could help people with skin damaged from radiation therapy (after 16-22 days).

A study published in the December 1999 American Journal of Clinical Nutrition found that "Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both."  In lab tests, EGCG, found in green tea, was found to prevent HIV from attacking T-Cells. However, it is not known if this has any effect on humans yet.

A study in the August, 2003 issue of a new potential application of Cellular and Molecular Life Sciences found that "a new potential application of (–)-epigallocatechin-3-gallate [a component of green tea] in prevention or treatment of inflammatory processes is suggested"

Historical references to tea's medicinal properties

The famous litterateur Sima Xiangru (179-117 BC) or the Western Han has recorded twenty kinds of medicine in the Sichuan area, tea being one of them.  Contempoary people believed that tea could not only make drunken people sober up, and keep people strong and energetic.  They also believed it could also help people dispel anxiety or irritation and even elevate them to be celestial.

A famous doctor in the Ming dynasty, Li Shizhen (1518-1593 AD) wrote in his  Compendium of Materia Medica, "Tea is bitter and cold, the coldest of colds and the most able to subdue the human heat.  Once the heat goes, the body goes right."

As a dried plant, tea preserves some vitamins and played an important role in keeping Chinese sailors' health in history, such as the voyage led by Zheng He.