Health benefits of tea
Encyclopedia
The health effects of tea have been examined ever since the first infusions of Camellia sinensis
about 4700 years ago in China. The legendary emperor Shennong
claimed in The Divine Farmer's Herb-Root Classic that Camellia sinensis infusions were useful for treating conditions including tumor
s, abscess
es, bladder
ailments, and lethargy. Possible beneficial health effects of tea consumption have been suggested and supported by some studies, but others have found no beneficial effects. The studies contrast other claims, including antinutritional effects such as preventing absorption of iron
and protein
, usually attributed to tannin. The vast majority of studies have been of green tea
; however, some studies have been made of the other types of tea derived from Camellia sinensis, such as white
, oolong
, and black tea
. Green tea has been claimed to be helpful for atherosclerosis
, LDL cholesterol
, cancer
, inflammatory bowel disease
, diabetes, liver disease
, weight loss
, neurodegenerative diseases, and even halitosis
.
, a type of antioxidant
. In a freshly picked tea leaf, catechins can compose up to 30% of the dry weight. Catechins are highest in concentration in white and green teas, while black tea has substantially fewer due to its oxidative preparation. Research by the U.S. Department of Agriculture has suggested that levels of antioxidants in green and black tea do not differ greatly, with green tea having an oxygen radical absorbance capacity
(ORAC) of 1253 and black tea an ORAC of 1128 (measured in μmolTE/100g). The amounts of carbohydrate
s, fat
, and protein
found in tea are negligible. Although tea contains various types of phenolics and tannin, tea does not contain tannic acid
. Tannic acid is not an appropriate standard for any type of tannin analysis because of its poorly defined composition.
and the stimulant caffeine
at about 3% of its dry weight, translating to between 30 mg and 90 mg per 8 oz (250 ml) cup depending on type, brand and brewing method. Tea also contains small amounts of theobromine
and theophylline
. Due to modern day environmental pollution fluoride
and aluminum have also been found to occur in tea, with certain types of brick tea
made from old leaves and stems having the highest levels. This occurs due to the tea plant's high sensitivity to and absorption of environmental pollutants. Dry tea has more caffeine by weight than coffee; nevertheless, more dried coffee is used than dry tea in preparing the beverage, which means that a cup of brewed tea contains significantly less caffeine than a cup of coffee of the same size.
properties due to their role in disrupting a specific stage of the bacterial DNA replication
process.
magazine mentions that numerous studies suggest that green tea
protects against a range of cancers, including lung, prostate and breast cancer. The reason cited is the antioxidant
epigallocatechin gallate
(EGCG), according to Hirofumi Tachibana's team at Kyushu University
. Their research showed that growth of human lung cancer cells with a cell receptor called 67 LR is slowed significantly after drinking just two or three cups of green tea, which contains EGCG. The research also showed that 67 LR is involved in the propagation of prion
diseases such as human Creutzfeldt-Jakob (related to mad cow disease in animals). This is not direct evidence of tea's effect on prion diseases, but a hint that EGCG's effect on 67 LR is an interesting lead in the search for treatments.
White tea
has been claimed to be more effective, based upon preliminary work by Santana-Rios et al.
Another study from the Life Science journal Carcinogenesis showed that green tea, in combination with tamoxifen
, is effective in suppressing breast cancer growth in vitro
human breast cancer tumors and in vivo
animal experiments in mice. A study at Taiwan
's Chung Shan Medical University
found that people who drank at least one cup of green tea per day were five times less likely to develop lung cancer than those who did not.
The anticarcinogenic effect of green tea on gastric cancer was refuted by a large-scale, population-based, prospective cohort study in Japan that involved more than 26,000 residents. Several case control studies suggest an inverse relation between green tea consumption and gastric cancer. Further evaluation is needed to assess the role of green tea and gastric cancer reduction.
Topical applications of green tea extracts (EGCG
) have protective effects on UVA
- and UVB
-induced skin damage (photoaging
and carcinogenesis
).
In a July 2005 review of claims made about the health benefits of green tea, the U.S. Food and Drug Administration
concluded that it was highly unlikely that green tea reduces the risk of breast and prostate cancer. The FDA believes that the evidence does not support qualified health claims for green tea consumption and a reduced risk of cancer.
s conducted by the University of Geneva
and the University of Birmingham
indicate that green tea raises metabolic rates, speeds up fat oxidation and improves insulin sensitivity and glucose tolerance. In addition to caffeine
, green tea contains catechin phenolics that raise thermogenesis
(the production of heat by the body), and hence increases energy expenditure.
There is also a suggestion that it can increase endurance in exercise by improving fat metabolism.
, although it is worth noting that this is evidence of an association, and that future studies are needed to confirm the effect.
L-theanine, found almost exclusively in the tea plant, and in the highest doses in green tea, actively alters the attention networks of the brain, according to results of human trials announced in September 2007. It has been proposed that theanine is absorbed by the small intestine and crosses the blood-brain barrier, where it affects the brain's neurotransmitters and increases alpha brain-wave
activity. The result is a calmer, yet more alert, state of mind.
released details of a research project which indicated that theanine
may help the body's immune system response when fighting infection, by boosting the disease-fighting capacity of gamma delta T cells. The study included a four-week trial with 11 coffee drinkers and 10 tea drinkers, who consumed 600ml of coffee or black tea daily. Blood sample analysis found that the production of anti-bacterial proteins was up to five times higher in the tea-drinkers, an indicator of a stronger immune response.
, which passes through the blood-brain barrier
.
In 2010 researchers found that people who consumed tea had significantly less cognitive decline than non-tea drinkers. Study participants who drank tea 5-10 times/year, 1-3 times/month, 1-4 times/week, and 5+ times/week had average annual rates of decline
17%, 32%, 37%, and 26% lower, respectively, than non-tea drinkers.
Coffee consumption did not show any effect except at the very highest level of consumption,
where it was associated with significantly decreased decline of 20 percent.
The study used data on more than 4,800 men and women aged 65 and older from the Cardiovascular Health Study to examine change in cognitive function over time. Study participants were followed for up to 14 years for naturally-occurring cognitive decline.
(AAICAD 2010; Lenore Arab, PhD;
UCLA http://www.alz.org/icad/2010_release_large_071110_1200pm.asp)
, drinking black tea can lead to lower levels of the stress hormone cortisol
after a stressful event. Fifty minutes after being subjected to challenging tasks, subjects who had been drinking 4 cups of black tea daily for 6 weeks, had a 20% greater drop in cortisol than the placebo group. Blood platelet
activation, which is linked to blood clotting and the risk of heart attacks was also lower for tea drinkers.
was the subject of an article on BBC News
. It stated that epigallocatechin gallate
(EGCG) found in green tea can lead to the inhibition of HIV binding and may be used as a complementary therapy for HIV patients, but qualified it by noting that "It is not a cure, and nor is it a safe way to avoid infection, however, we suggest that it should be used in combination with conventional medicines to improve quality of life for those infected." It was an in vitro
(test tube) study, not an in vivo
study, which only tested effects of a chemical in green tea. "Many substances shown to prevent HIV infection in the test tube turn out to have little or no effect in real life, so I think there's a long way to go before anyone should rely on green tea to protect against HIV infection."
stated that tea phenolics help inhibit the growth of bacteria that cause bad breath.
and a temporary increase in short term memory. Further, caffeine consumption has been linked with greater athletic performance, healthy weight loss, reduction in duration and severity of headaches and is effective in treating the symptoms of asthma.
, in the second issue for May, 2008 of the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine. Researchers examined the effects of green tea phenolics administered through drinking water, on rats that were intermittently deprived of oxygen during 12-hour “night” cycles, mimicking the intermittent hypoxia that humans with OSA experience.
(May 2008) found white tea extracts effective at treating bacterial infections, such as Staphylococcus
, Streptococcus
, pneumonia
and dental caries
. White tea was also found to be effective in treating fungal infections from Penicillium chrysogenum
and Saccharomyces cerevisiae
. Researchers also reported that white tea extracts showed a greater effect than green tea extracts.
(UCLA) and presented at the International Stroke Conference in February 2009 found that drinking three or more cups of either green or black tea per day can reduce the risk of suffering a stroke
by as much as 21%.
and funded by the Unilever
-owned Lipton Institute of Tea
suggests that drinking just one cup of regular, black tea per day may help to protect against cardiovascular disease. The research showed that black tea consumption does—depending on dose—improve blood vessel reactivity, reduce both blood pressure and arterial stiffness, indicating a notably better cardiovascular health profile.
A more frequent consumption of green tea was associated with a lower prevalence of depressive symptoms in another Japanese study. Researchers conducted a cross-sectional study in 1,058 community-dwelling elderly Japanese individuals 70 years of age. The prevalence of mild and severe depressive symptoms was 34.1 percent and 20.2 percent, respectively. After adjustment for confounding factors, the odds ratios for mild and severe depressive symptoms when higher green tea consumption was compared with green tea consumption of 1 cup/d were: 2 to 3 cups green tea/d and 4 cups green tea/d. Similar relations were also observed in the case of severe depressive symptoms.
; however, mature leaves contain as much as 10 to 20 times the fluoride levels of young leaves from the same plant. High fluoride intake (daily intakes over 2 mg for children, 4 mg adults) increases the risk of osteofluorosis and fractures. It is speculated that hand-picked tea would contain less fluoride than machine-harvested tea, because there is a much lower chance of harvesting older leaves during the harvest process. There is some evidence that over-intake of teas produced using mature leaves (e.g. brick tea) or a combination of mature and young (e.g. through inefficient mechanical harvesting) has been found to cause fluorosis in humans
The fluoride content of made tea depends on the picking method and fluoride content of the soil in which it is grown; tea plants absorbs this element at a greater rate than other plants. Care in the choice of the location where the plant is grown may reduce the risk.
in the long-term. While large doses of Aluminum can cause toxicity in humans, which may even result in death, there is no evidence that consuming any quantity of made tea has had this result.
Caffeine
is an addictive
drug
and overuse of tea may result in harmful side effects, such as an increased likelihood of certain sleep disorder
s. Decaffeination reduces total catechins in both black and green dry teas by about 15 times and 3 times respectively.
One consideration to take into account when investigating the relationship between caffeine and diuresis
is the amount of caffeine ingested. However, the British Dietetic Association
has suggested that tea can be used to supplement normal water consumption, and that "the style of tea and coffee and the amounts we drink in the UK are unlikely to have a negative effect [on hydration]".
, overconsumption of which can cause kidney
stones, as well as binding with free calcium
in the body; other minerals may be bound as well. The bioavailability
of oxalate from tea is low, thus negative effect requires a large intake of tea.
, with some studies having found that tea drinking may in fact be negatively associated with risk of esophageal cancer.
: "In the case-control study, risk for esophageal cancer was increased for drinking hot tea vs lukewarm or warm tea. Risk was also significantly increased for drinking tea 2 to 3 minutes after pouring, or less than 2 minutes after pouring vs drinking tea at least 4 minutes after being poured." However, the act of boiling the water in the preparation of tea is known to kill harmful bacteria in the water and can be particularly beneficial in countries with lower quality drinking water.
(415 mg of a mixture of green, white, and oolong tea extracts, and several other herbal extracts, per dose); Exolise (360 mg of green tea extract per dose); and Tealine (250 mg of green tea extract per dose). These concerns resulted in withdrawals of the first two products and a class action lawsuit against the manufacturer of Hydroxycut. The risk is thought to be quite small: in case of Hydroxycut, 9 million bottles were sold in the U.S. over the lifetime of the product, resulting in 23 known severe cases, however, these included at least one fatality and at least three cases of liver failure resulting in a liver transplantation. In case of Exolise, the risk of an adverse effect was estimated as less than 1 per 100,000. The mechanism is not completely understood, but it is thought that, in some genetically predisposed individuals, regular consumption of green tea, particularly when combined with fasting, can result in accumulation of a flavonoid EGCG
(only present in green tea, but not in black tea) in the bloodstream to unsafe levels.
of the Berlin Universities showed that adding milk
to tea will block the normal, healthful effects that tea has in protecting against cardiovascular disease
. This occurs because casein
from the milk binds to the molecules in tea that cause the arteries to relax, especially EGCG
. Milk may also block tea's effect on other things, such as cancer. Other studies have found little to no effect from milk on the observed increase in total plasma antioxidant activity. Teas with high EGCG content, such as green tea, are not typically consumed with milk. Previous studies have observed a beneficial effect from black tea which was not attributable to the catechin content. Plant-based "milks", such as soy milk
, do not contain casein and are not known to have similar effects on tea.
Milk binds catechins, most notably EGCG. Milk also binds tannin, rendering it harmless, which helps to exemplify the effect on tea's constituent parts (i.e. EGCG binding).
such as lemon juice is common. Studies, including a study from Purdue University in 2007, found that most of the antioxidant catechins are not absorbed into the bloodstream when tea is drunk by itself. The study, however, found that adding citrus to the tea lowers the pH in the small intestine
and causes more of the catechins to be absorbed.
Camellia sinensis
Camellia sinensis is the species of plant whose leaves and leaf buds are used to produce Chinese tea. It is of the genus Camellia , a genus of flowering plants in the family Theaceae. White tea, green tea, oolong, pu-erh tea and black tea are all harvested from this species, but are processed...
about 4700 years ago in China. The legendary emperor Shennong
Shennong
Shennong , which names mean "Divine Farmer", but also known as the Emperor of the Five Grains , was a legendary ruler of China and culture hero reputed to have lived some 5,000 years ago...
claimed in The Divine Farmer's Herb-Root Classic that Camellia sinensis infusions were useful for treating conditions including tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s, abscess
Abscess
An abscess is a collection of pus that has accumulated in a cavity formed by the tissue in which the pus resides due to an infectious process or other foreign materials...
es, bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
ailments, and lethargy. Possible beneficial health effects of tea consumption have been suggested and supported by some studies, but others have found no beneficial effects. The studies contrast other claims, including antinutritional effects such as preventing absorption of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
, usually attributed to tannin. The vast majority of studies have been of green tea
Green tea
Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally...
; however, some studies have been made of the other types of tea derived from Camellia sinensis, such as white
White tea
White tea is a lightly oxidized tea grown and harvested almost exclusively in China, primarily in the Fujian province.White tea comes from the delicate buds and younger leaves of the Chinese Camellia sinensis plant. These buds and leaves are allowed to wither in natural sunlight before they are...
, oolong
Oolong
Oolong is a traditional Chinese tea produced through a unique process including withering under the strong sun and oxidation before curling and twisting. Most oolong teas, especially those of fine quality, involve unique tea plant cultivars that are exclusively used for particular varieties...
, and black tea
Black tea
Black tea is a variety of tea that is more oxidized than the oolong, green, and white varieties.All four varieties are made from leaves of the shrub Camellia sinensis. Black tea is generally stronger in flavor and contains more caffeine than the less oxidized teas. Two principal varieties of the...
. Green tea has been claimed to be helpful for atherosclerosis
Atherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
, LDL cholesterol
Low density lipoprotein
Low-density lipoprotein is one of the five major groups of lipoproteins, which in order of size, largest to smallest, are chylomicrons, VLDL, IDL, LDL, and HDL, that enable transport of cholesterol within the water-based bloodstream...
, cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
, inflammatory bowel disease
Inflammatory bowel disease
In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis.-Classification:...
, diabetes, liver disease
Liver disease
Liver disease is a broad term describing any single number of diseases affecting the liver.-Diseases:* Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons , autoimmunity or hereditary conditions...
, weight loss
Weight loss
Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...
, neurodegenerative diseases, and even halitosis
Halitosis
Halitosis is a term used to describe noticeably unpleasant odors exhaled in breathing. Halitosis is estimated to be the third most frequent reason for seeking dental aid, following tooth decay and periodontal disease.- General :...
.
Content
Tea contains catechinsFlavan-3-ol
Flavan-3-ols are a class of flavonoids that use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. These compounds include the catechins and the catechin gallates....
, a type of antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
. In a freshly picked tea leaf, catechins can compose up to 30% of the dry weight. Catechins are highest in concentration in white and green teas, while black tea has substantially fewer due to its oxidative preparation. Research by the U.S. Department of Agriculture has suggested that levels of antioxidants in green and black tea do not differ greatly, with green tea having an oxygen radical absorbance capacity
Oxygen radical absorbance capacity
Oxygen Radical Absorbance Capacity is a method of measuring antioxidant capacities in biological samples in vitro.A wide variety of foods has been tested using this method, with certain spices, berries and legumes rated highly. There exists no physiological proof in vivo that free-radical theory...
(ORAC) of 1253 and black tea an ORAC of 1128 (measured in μmolTE/100g). The amounts of carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
s, fat
Vegetable fats and oils
Vegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure...
, and protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
found in tea are negligible. Although tea contains various types of phenolics and tannin, tea does not contain tannic acid
Tannic acid
Tannic acid is a specific commercial form of tannin, a type of polyphenol. Its weak acidity is due to the numerous phenol groups in the structure...
. Tannic acid is not an appropriate standard for any type of tannin analysis because of its poorly defined composition.
Theanine and caffeine
Tea also contains theanineTheanine
Theanine , also gamma-glutamylethylamide or 5-N-ethyl-glutamine, is an amino acid and a glutamic acid analog commonly found in tea , primarily in green tea, and also in the basidiomycete mushroom Boletus badius and in guayusa. More specifically, this compound is called L-theanine, being the...
and the stimulant caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
at about 3% of its dry weight, translating to between 30 mg and 90 mg per 8 oz (250 ml) cup depending on type, brand and brewing method. Tea also contains small amounts of theobromine
Theobromine
Theobromine , also known as xantheose, is a bitter alkaloid of the cacao plant, with the chemical formula C7H8N4O2. It is found in chocolate, as well as in a number of other foods, including the leaves of the tea plant, and the kola nut...
and theophylline
Theophylline
Theophylline, also known as dimethylxanthine, is a methylxanthine drug used in therapy for respiratory diseases such as COPD and asthma under a variety of brand names. Because of its numerous side-effects, the drug is now rarely administered for clinical use. As a member of the xanthine family, it...
. Due to modern day environmental pollution fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
and aluminum have also been found to occur in tea, with certain types of brick tea
Tea brick
Tea bricks or compressed tea are blocks of whole or finely ground black tea, green tea, or post-fermented tea leaves that have been packed in molds and pressed into block form...
made from old leaves and stems having the highest levels. This occurs due to the tea plant's high sensitivity to and absorption of environmental pollutants. Dry tea has more caffeine by weight than coffee; nevertheless, more dried coffee is used than dry tea in preparing the beverage, which means that a cup of brewed tea contains significantly less caffeine than a cup of coffee of the same size.
Antibiotic effects
Green tea catechins have also been shown to possess antibioticAntibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
properties due to their role in disrupting a specific stage of the bacterial DNA replication
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
process.
Anti-cancer properties
An article in New ScientistNew Scientist
New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...
magazine mentions that numerous studies suggest that green tea
Green tea
Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally...
protects against a range of cancers, including lung, prostate and breast cancer. The reason cited is the antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
epigallocatechin gallate
Epigallocatechin gallate
Epigallocatechin gallate , also known as epigallocatechin 3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin....
(EGCG), according to Hirofumi Tachibana's team at Kyushu University
Kyushu University
Kyushu University is one of the most prestigious universities in Japan. It can be seen in the several rankings such as shown below.-General Rankings:The university has been ranked 8th in 2010 and 2009 in the ranking "Truly Strong Universities" by Toyo Keizai...
. Their research showed that growth of human lung cancer cells with a cell receptor called 67 LR is slowed significantly after drinking just two or three cups of green tea, which contains EGCG. The research also showed that 67 LR is involved in the propagation of prion
Prion
A prion is an infectious agent composed of protein in a misfolded form. This is in contrast to all other known infectious agents which must contain nucleic acids . The word prion, coined in 1982 by Stanley B. Prusiner, is a portmanteau derived from the words protein and infection...
diseases such as human Creutzfeldt-Jakob (related to mad cow disease in animals). This is not direct evidence of tea's effect on prion diseases, but a hint that EGCG's effect on 67 LR is an interesting lead in the search for treatments.
White tea
White tea
White tea is a lightly oxidized tea grown and harvested almost exclusively in China, primarily in the Fujian province.White tea comes from the delicate buds and younger leaves of the Chinese Camellia sinensis plant. These buds and leaves are allowed to wither in natural sunlight before they are...
has been claimed to be more effective, based upon preliminary work by Santana-Rios et al.
Another study from the Life Science journal Carcinogenesis showed that green tea, in combination with tamoxifen
Tamoxifen
Tamoxifen is an antagonist of the estrogen receptor in breast tissue via its active metabolite, hydroxytamoxifen. In other tissues such as the endometrium, it behaves as an agonist, hence tamoxifen may be characterized as a mixed agonist/antagonist...
, is effective in suppressing breast cancer growth in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
human breast cancer tumors and in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
animal experiments in mice. A study at Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
's Chung Shan Medical University
Chung Shan Medical University
Chung Shan Medical University is a medical university, located in Taichung City, Taiwan. It is close to the Daqing railway station.- Campus :...
found that people who drank at least one cup of green tea per day were five times less likely to develop lung cancer than those who did not.
The anticarcinogenic effect of green tea on gastric cancer was refuted by a large-scale, population-based, prospective cohort study in Japan that involved more than 26,000 residents. Several case control studies suggest an inverse relation between green tea consumption and gastric cancer. Further evaluation is needed to assess the role of green tea and gastric cancer reduction.
Topical applications of green tea extracts (EGCG
Epigallocatechin gallate
Epigallocatechin gallate , also known as epigallocatechin 3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin....
) have protective effects on UVA
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
- and UVB
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
-induced skin damage (photoaging
Photoaging
Photoaging or photoageing is a term used for the characteristic changes induced by chronic UVA and UVB exposure. Tretinoin is the best studied retinoid in the treatment of photoaging...
and carcinogenesis
Carcinogenesis
Carcinogenesis or oncogenesis is literally the creation of cancer. It is a process by which normal cells are transformed into cancer cells...
).
In a July 2005 review of claims made about the health benefits of green tea, the U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
concluded that it was highly unlikely that green tea reduces the risk of breast and prostate cancer. The FDA believes that the evidence does not support qualified health claims for green tea consumption and a reduced risk of cancer.
Increases metabolic rate
Clinical trialClinical trial
Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...
s conducted by the University of Geneva
University of Geneva
The University of Geneva is a public research university located in Geneva, Switzerland.It was founded in 1559 by John Calvin, as a theological seminary and law school. It remained focused on theology until the 17th century, when it became a center for Enlightenment scholarship. In 1873, it...
and the University of Birmingham
University of Birmingham
The University of Birmingham is a British Redbrick university located in the city of Birmingham, England. It received its royal charter in 1900 as a successor to Birmingham Medical School and Mason Science College . Birmingham was the first Redbrick university to gain a charter and thus...
indicate that green tea raises metabolic rates, speeds up fat oxidation and improves insulin sensitivity and glucose tolerance. In addition to caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
, green tea contains catechin phenolics that raise thermogenesis
Thermogenesis
Thermogenesis is the process of heat production in organisms. It occurs mostly in warm-blooded animals, but a few species of thermogenic plants exist.-Types:...
(the production of heat by the body), and hence increases energy expenditure.
There is also a suggestion that it can increase endurance in exercise by improving fat metabolism.
Possible anti-diabetes effect
There is also epidemiological evidence that drinking green tea and black tea may help prevent diabetesDiabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
, although it is worth noting that this is evidence of an association, and that future studies are needed to confirm the effect.
Boosts mental alertness
The amino acidAmino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
L-theanine, found almost exclusively in the tea plant, and in the highest doses in green tea, actively alters the attention networks of the brain, according to results of human trials announced in September 2007. It has been proposed that theanine is absorbed by the small intestine and crosses the blood-brain barrier, where it affects the brain's neurotransmitters and increases alpha brain-wave
Alpha wave
Alpha waves are neural oscillations in the frequency range of 8–12 Hz arising from synchronous and coherent electrical activity of thalamic pacemaker cells in humans...
activity. The result is a calmer, yet more alert, state of mind.
Boosts immune system
On 21 April 2003 the Brigham and Women's HospitalBrigham and Women's Hospital
Brigham and Women's Hospital is the largest hospital of the Longwood Medical and Academic Area in Boston, Massachusetts. It is directly adjacent to Harvard Medical School of which it is the second largest teaching affiliate with 793 beds...
released details of a research project which indicated that theanine
Theanine
Theanine , also gamma-glutamylethylamide or 5-N-ethyl-glutamine, is an amino acid and a glutamic acid analog commonly found in tea , primarily in green tea, and also in the basidiomycete mushroom Boletus badius and in guayusa. More specifically, this compound is called L-theanine, being the...
may help the body's immune system response when fighting infection, by boosting the disease-fighting capacity of gamma delta T cells. The study included a four-week trial with 11 coffee drinkers and 10 tea drinkers, who consumed 600ml of coffee or black tea daily. Blood sample analysis found that the production of anti-bacterial proteins was up to five times higher in the tea-drinkers, an indicator of a stronger immune response.
Lowers chances of cognitive impairment
A 2006 study showed that elderly Japanese people who consumed more than 2 cups of green tea a day had a 50 percent lower chance of having cognitive impairment, in comparison to those who drank fewer than 2 cups a day, or who consumed other tested beverages. This is probably due to the effect of EGCGEpigallocatechin gallate
Epigallocatechin gallate , also known as epigallocatechin 3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin....
, which passes through the blood-brain barrier
Blood-brain barrier
The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...
.
In 2010 researchers found that people who consumed tea had significantly less cognitive decline than non-tea drinkers. Study participants who drank tea 5-10 times/year, 1-3 times/month, 1-4 times/week, and 5+ times/week had average annual rates of decline
17%, 32%, 37%, and 26% lower, respectively, than non-tea drinkers.
Coffee consumption did not show any effect except at the very highest level of consumption,
where it was associated with significantly decreased decline of 20 percent.
The study used data on more than 4,800 men and women aged 65 and older from the Cardiovascular Health Study to examine change in cognitive function over time. Study participants were followed for up to 14 years for naturally-occurring cognitive decline.
(AAICAD 2010; Lenore Arab, PhD;
UCLA http://www.alz.org/icad/2010_release_large_071110_1200pm.asp)
Lowers stress hormone levels
According to a study by researchers at University College LondonUniversity College London
University College London is a public research university located in London, United Kingdom and the oldest and largest constituent college of the federal University of London...
, drinking black tea can lead to lower levels of the stress hormone cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
after a stressful event. Fifty minutes after being subjected to challenging tasks, subjects who had been drinking 4 cups of black tea daily for 6 weeks, had a 20% greater drop in cortisol than the placebo group. Blood platelet
Platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days...
activation, which is linked to blood clotting and the risk of heart attacks was also lower for tea drinkers.
Effects on HIV
A recent study appearing in the Journal of Allergy and Clinical ImmunologyJournal of Allergy and Clinical Immunology
The Journal of Allergy and Clinical Immunology is a medical journal in the field of allergy and immunology. It is the official journal of the American Academy of Allergy, Asthma, and Immunology. The journal was established in 1929 as the Journal of Allergy and obtained its current name in 1971...
was the subject of an article on BBC News
BBC News
BBC News is the department of the British Broadcasting Corporation responsible for the gathering and broadcasting of news and current affairs. The department is the world's largest broadcast news organisation and generates about 120 hours of radio and television output each day, as well as online...
. It stated that epigallocatechin gallate
Flavonoid
Flavonoids , are a class of plant secondary metabolites....
(EGCG) found in green tea can lead to the inhibition of HIV binding and may be used as a complementary therapy for HIV patients, but qualified it by noting that "It is not a cure, and nor is it a safe way to avoid infection, however, we suggest that it should be used in combination with conventional medicines to improve quality of life for those infected." It was an in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
(test tube) study, not an in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
study, which only tested effects of a chemical in green tea. "Many substances shown to prevent HIV infection in the test tube turn out to have little or no effect in real life, so I think there's a long way to go before anyone should rely on green tea to protect against HIV infection."
Effects on inflammatory bowel disease (IBD)
The phenolics in green tea have been shown to reduce intestinal inflammation in mouse models of IBD. This effect seems to be related to tea’s ability to interrupt the cascade of inflammatory reactions that are the cause of IBD.Effects on bad breath
Researchers at the University of Illinois at ChicagoUniversity of Illinois at Chicago
The University of Illinois at Chicago, or UIC, is a state-funded public research university located in Chicago, Illinois, United States. Its campus is in the Near West Side community area, near the Chicago Loop...
stated that tea phenolics help inhibit the growth of bacteria that cause bad breath.
Iron overload disorders
Researchers in Germany have found that a daily cup of black tea can help stop excess iron damaging the bodies of people who suffer from hemochromatosis due to its high content of flavonoids (commonly mistaken for tannins), which limit iron absorption.Effects associated with caffeine
A cup of green tea contains between 15 and 50 mg of caffeine. Certain cognitive benefits are associated with caffeine consumption, such as a reduction in the likelihood of Parkinson's diseaseParkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...
and a temporary increase in short term memory. Further, caffeine consumption has been linked with greater athletic performance, healthy weight loss, reduction in duration and severity of headaches and is effective in treating the symptoms of asthma.
Effects on obstructive sleep apnea-related brain deficits
University of Louisville researchers report that green tea phenolics may stave off the cognitive deficits that occur with obstructive sleep apneaSleep apnea
Sleep apnea is a sleep disorder characterized by abnormal pauses in breathing or instances of abnormally low breathing, during sleep. Each pause in breathing, called an apnea, can last from a few seconds to minutes, and may occur 5 to 30 times or more an hour. Similarly, each abnormally low...
, in the second issue for May, 2008 of the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine. Researchers examined the effects of green tea phenolics administered through drinking water, on rats that were intermittently deprived of oxygen during 12-hour “night” cycles, mimicking the intermittent hypoxia that humans with OSA experience.
Effects on bacterial and fungal infections
A study at Pace University reported in American Society For MicrobiologyAmerican Society for Microbiology
The American Society for Microbiology is a professional organization for scientists who study viruses, bacteria, fungi, algae, and protozoa as well as other aspects of microbiology. Microbiology is the study of organisms too small to be seen with the naked eye and which must be viewed with a...
(May 2008) found white tea extracts effective at treating bacterial infections, such as Staphylococcus
Staphylococcus
Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....
, Streptococcus
Streptococcus
Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
, pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
and dental caries
Dental caries
Dental caries, also known as tooth decay or a cavity, is an irreversible infection usually bacterial in origin that causes demineralization of the hard tissues and destruction of the organic matter of the tooth, usually by production of acid by hydrolysis of the food debris accumulated on the...
. White tea was also found to be effective in treating fungal infections from Penicillium chrysogenum
Penicillium chrysogenum
Penicillium chrysogenum is common in temperate and subtropical regions and can be found on salted food products, but it is mostly found in indoor environments, especially in damp or waterdamaged buildings. It was previously known as Penicillium notatum. It has rarely been reported as a cause of...
and Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
. Researchers also reported that white tea extracts showed a greater effect than green tea extracts.
Anti-venom effects
Antivenin activity of melanin extracted from black tea (MEBT) was reported for the first time in 2004. Low toxicity of MEBT in combination with its antagonistic activity against different venoms may allow effective life-saving treatment against snakebites. Such application of MEBT is important when identification of the snake is impossible or if specific treatment is unavailable.Stroke
Research conducted at the University of California, Los AngelesUniversity of California, Los Angeles
The University of California, Los Angeles is a public research university located in the Westwood neighborhood of Los Angeles, California, USA. It was founded in 1919 as the "Southern Branch" of the University of California and is the second oldest of the ten campuses...
(UCLA) and presented at the International Stroke Conference in February 2009 found that drinking three or more cups of either green or black tea per day can reduce the risk of suffering a stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
by as much as 21%.
Cardiovascular health
Research published in April 2009 by the University of L'AquilaUniversity of L'Aquila
The University of L'Aquila is a university located in L'Aquila, central Italy. It was founded in 1964 and is organized in nine faculties.Presents a scientific-technological character with many research groups. Its faculties occupy a high position between the Italian universities...
and funded by the Unilever
Unilever
Unilever is a British-Dutch multinational corporation that owns many of the world's consumer product brands in foods, beverages, cleaning agents and personal care products....
-owned Lipton Institute of Tea
Lipton Institute of Tea
The Lipton Institute of Tea is a dedicated tea research facility owned by consumer goods company Unilever, which also owns the Lipton tea brand. The Institute conducts studies on the mental and physical health benefits of tea...
suggests that drinking just one cup of regular, black tea per day may help to protect against cardiovascular disease. The research showed that black tea consumption does—depending on dose—improve blood vessel reactivity, reduce both blood pressure and arterial stiffness, indicating a notably better cardiovascular health profile.
Anogenital warts
Sinecatechin, an extract from green tea, was shown to be effective in treating anogenital warts in a double-blinded, randomized controlled trial of greater than 500 subjects. The subjects applied a topical ointment containing either sinecatechin or placebo to the affected area for up to 4 months, and were followed for 3 months after treatment. More than half of the subjects in the treatment group (57%) experienced a complete resolution of their warts, compared with a third (34%) in the control group. 78% of the patients in the treatment group experienced at least 50% improvement in their warts. The number needed to treat was 4-5 patients. The green tea extract treatment was well-tolerated, with relatively few side-effects.Antidepressant properties
In a Japanese study, green tea consumption was inversely associated with psychological distress even after adjustment for possible confounding factors.A more frequent consumption of green tea was associated with a lower prevalence of depressive symptoms in another Japanese study. Researchers conducted a cross-sectional study in 1,058 community-dwelling elderly Japanese individuals 70 years of age. The prevalence of mild and severe depressive symptoms was 34.1 percent and 20.2 percent, respectively. After adjustment for confounding factors, the odds ratios for mild and severe depressive symptoms when higher green tea consumption was compared with green tea consumption of 1 cup/d were: 2 to 3 cups green tea/d and 4 cups green tea/d. Similar relations were also observed in the case of severe depressive symptoms.
Rheumatoid arthritis
One study shows that green tea reduced the severity of rheumatoid arthritis in rats; however another study shows that tea increases the risk for rheumatoid arthritis by 78% for heavy drinkers and by 40% for occasional drinkers.Weight loss and cholesterol
Green tea and its extract have been shown to fight obesity and lower LDL "bad" cholesterol—two risk factors for heart disease and diabetes. One study in the Netherlands and a study in Japan showed that green tea did both. In the Dutch study, participants who drank caffeinated green tea lost more weight, but even those who typically drank the decaf variety saw a decrease in their waistlines and body weight. Researchers speculated that the caffeine helps with fat oxidation. In the Japanese study, 240 men and women were given varying amounts of green tea extract for three months. Those who got the highest amount lost fat and weight and had lower blood pressure and lower LDL "bad" cholesterol.Fluoride
All tea leaves contain fluorideFluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
; however, mature leaves contain as much as 10 to 20 times the fluoride levels of young leaves from the same plant. High fluoride intake (daily intakes over 2 mg for children, 4 mg adults) increases the risk of osteofluorosis and fractures. It is speculated that hand-picked tea would contain less fluoride than machine-harvested tea, because there is a much lower chance of harvesting older leaves during the harvest process. There is some evidence that over-intake of teas produced using mature leaves (e.g. brick tea) or a combination of mature and young (e.g. through inefficient mechanical harvesting) has been found to cause fluorosis in humans
The fluoride content of made tea depends on the picking method and fluoride content of the soil in which it is grown; tea plants absorbs this element at a greater rate than other plants. Care in the choice of the location where the plant is grown may reduce the risk.
Aluminum
Like Fluorine, the tea plant is a natural bioaccumulator of Aluminum, particularly in older leaves, with Aluminum concentrations of up to 30,000 ppm Aluminum by dry weight . Again, machine-harvested tea leaves are thought to be higher in free Aluminum than those harvested by hand, since harvesting machines are more likely to inadvertently harvest older leaves during harvest. While there is considerable debate over the health effects of aluminum, there is a substantial body of evidence that excessive aluminum intake may lead to Alzheimer's DiseaseAlzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
in the long-term. While large doses of Aluminum can cause toxicity in humans, which may even result in death, there is no evidence that consuming any quantity of made tea has had this result.
Caffeine
- For health issues see main article Health effects of caffeineHealth effects of caffeineThe health effects of caffeine have been extensively studied. Short term side effects such as headache, nausea, and anxiety have been shown as symptoms of mild caffeine consumption. The long term consequences of moderate caffeine consumption can be reduced risk of developing Parkinson's disease,...
.
Caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
is an addictive
Substance dependence
The section about substance dependence in the Diagnostic and Statistical Manual of Mental Disorders does not use the word addiction at all. It explains:...
drug
Drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...
and overuse of tea may result in harmful side effects, such as an increased likelihood of certain sleep disorder
Sleep disorder
A sleep disorder, or somnipathy, is a medical disorder of the sleep patterns of a person or animal. Some sleep disorders are serious enough to interfere with normal physical, mental and emotional functioning...
s. Decaffeination reduces total catechins in both black and green dry teas by about 15 times and 3 times respectively.
One consideration to take into account when investigating the relationship between caffeine and diuresis
Polyuria
Polyuria is a condition usually defined as excessive or abnormally large production or passage of urine . Frequent urination is sometimes included by definition, but is nonetheless usually an accompanying symptom...
is the amount of caffeine ingested. However, the British Dietetic Association
British Dietetic Association
The British Dietetic Association is a professional association and trade union for dieticians in the United Kingdom. It was founded in 1936 and became a certified union in 1982; it is affiliated to the Trades Union Congress and the Scottish Trades Union Congress.The BDA was established in 1936...
has suggested that tea can be used to supplement normal water consumption, and that "the style of tea and coffee and the amounts we drink in the UK are unlikely to have a negative effect [on hydration]".
Oxalates
Tea contains oxalateOxalate
Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...
, overconsumption of which can cause kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
stones, as well as binding with free calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
in the body; other minerals may be bound as well. The bioavailability
Bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered...
of oxalate from tea is low, thus negative effect requires a large intake of tea.
Tannin
It has been suggested that chemicals known as tannins may increase one's risk of esophageal cancerEsophageal cancer
Esophageal cancer is malignancy of the esophagus. There are various subtypes, primarily squamous cell cancer and adenocarcinoma . Squamous cell cancer arises from the cells that line the upper part of the esophagus...
, with some studies having found that tea drinking may in fact be negatively associated with risk of esophageal cancer.
Hot drinking temperature
Hot tea consumption has been linked to a higher risk for esophageal cancerEsophageal cancer
Esophageal cancer is malignancy of the esophagus. There are various subtypes, primarily squamous cell cancer and adenocarcinoma . Squamous cell cancer arises from the cells that line the upper part of the esophagus...
: "In the case-control study, risk for esophageal cancer was increased for drinking hot tea vs lukewarm or warm tea. Risk was also significantly increased for drinking tea 2 to 3 minutes after pouring, or less than 2 minutes after pouring vs drinking tea at least 4 minutes after being poured." However, the act of boiling the water in the preparation of tea is known to kill harmful bacteria in the water and can be particularly beneficial in countries with lower quality drinking water.
Risk of liver damage
Consumption of some forms of tea has the potential to result in acute liver damage in some individuals. Several herbal & dietary supplements have been linked to liver damage, caused in part or completely by the presence of green tea extract in these supplements; the most notable cases include HydroxycutHydroxycut
Hydroxycut is the brand name of a series of dietary supplements marketed as an aid to weight loss. According to a 2009 paper in the World Journal of Gastroenterology, Hydroxycut is the most popular brand of weight-loss supplement, selling approximately 1 million units per year. On May 1, 2009, the...
(415 mg of a mixture of green, white, and oolong tea extracts, and several other herbal extracts, per dose); Exolise (360 mg of green tea extract per dose); and Tealine (250 mg of green tea extract per dose). These concerns resulted in withdrawals of the first two products and a class action lawsuit against the manufacturer of Hydroxycut. The risk is thought to be quite small: in case of Hydroxycut, 9 million bottles were sold in the U.S. over the lifetime of the product, resulting in 23 known severe cases, however, these included at least one fatality and at least three cases of liver failure resulting in a liver transplantation. In case of Exolise, the risk of an adverse effect was estimated as less than 1 per 100,000. The mechanism is not completely understood, but it is thought that, in some genetically predisposed individuals, regular consumption of green tea, particularly when combined with fasting, can result in accumulation of a flavonoid EGCG
Epigallocatechin gallate
Epigallocatechin gallate , also known as epigallocatechin 3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin....
(only present in green tea, but not in black tea) in the bloodstream to unsafe levels.
Effect of milk on tea
A study at the Charité HospitalCharité
The Charité - Universitätsmedizin Berlin is the medical school for both the Humboldt University and the Free University of Berlin. After the merger with their fourth campus in 2003, the Charité is one of the largest university hospitals in Europe....
of the Berlin Universities showed that adding milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
to tea will block the normal, healthful effects that tea has in protecting against cardiovascular disease
Cardiovascular disease
Heart disease or cardiovascular disease are the class of diseases that involve the heart or blood vessels . While the term technically refers to any disease that affects the cardiovascular system , it is usually used to refer to those related to atherosclerosis...
. This occurs because casein
Casein
Casein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....
from the milk binds to the molecules in tea that cause the arteries to relax, especially EGCG
Epigallocatechin gallate
Epigallocatechin gallate , also known as epigallocatechin 3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin....
. Milk may also block tea's effect on other things, such as cancer. Other studies have found little to no effect from milk on the observed increase in total plasma antioxidant activity. Teas with high EGCG content, such as green tea, are not typically consumed with milk. Previous studies have observed a beneficial effect from black tea which was not attributable to the catechin content. Plant-based "milks", such as soy milk
Soy milk
Soy milk and sometimes referred to as soy drink/beverage is a beverage made from soybeans. A stable emulsion of oil, water, and protein, it is produced by soaking dry soybeans and grinding them with water...
, do not contain casein and are not known to have similar effects on tea.
Milk binds catechins, most notably EGCG. Milk also binds tannin, rendering it harmless, which helps to exemplify the effect on tea's constituent parts (i.e. EGCG binding).
Effect of citrus on tea
Drinking tea, particularly green tea, with citrusCitrus
Citrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...
such as lemon juice is common. Studies, including a study from Purdue University in 2007, found that most of the antioxidant catechins are not absorbed into the bloodstream when tea is drunk by itself. The study, however, found that adding citrus to the tea lowers the pH in the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
and causes more of the catechins to be absorbed.
See also
- Phenolic content in tea
- Health effects of coffee
- Traditional medicineTraditional medicineTraditional medicine comprises unscientific knowledge systems that developed over generations within various societies before the era of modern medicine...
- Mexican tea cultureMexican tea cultureMexican tea culture is known for its traditional herbal teas which are reputed to have medicinal properties. In recent decades, imported tea beverages have also become popular in Mexico. Mexican tea recipes have grown in popularity beyond Mexico as well....
- Brazilian tea cultureBrazilian tea cultureBrazilian tea culture has its origins with teas made by the indigenous cultures of the Amazon region. It has evolved since the Portuguese colonial period to include imported varieties and tea-drinking customs.-Erva mate:...
External links
- Some evidence for the benefits of green tea for endurance in exercise
- Tea and Cancer Prevention - National Cancer Institute press release
- Antioxidant in Green Tea May Fight Alzheimer's, (EGCG)
- Green Tea (an overview from Drugs.com)
- "Tea 'healthier' drink than water" - BBCBBCThe British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
article, 24 August 2006 - Green tea might prolong life and help skin damaged from radiation therapy