Potential effects of tea on health
Potential effects of tea on health have been touted for infusions made from the plant Camellia sinensis for over 4700 years; ever since its discovery was attributed to the legendary emperor, Shennong. The Shen Nong Ben Cao Jing claimed its taste and stimulative properties were useful for treating tumors, abscesses, bladder ailments, lethargy, among other conditions. The 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 tea, Oolong tea, 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.

# Potential benefits

## Anti-cancer properties
An article in New Scientist 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 in Japan. Their research showed that growth of human lung cancer cells that have 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.
According to the U.S. National Cancer Institute, in laboratory studies using animals, catechins inactivated oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells.
White tea has been claimed to be even more effective, based upon preliminary work by Santana-Rios et al.
Another study from the Oxford Life Science journal Carcinogenesis showing a capacity of 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.
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 (reference: New England Journal of Medicine 2001;344:632, Tsubono F, Nishino Y).  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. (Reference: Textbook of Gastroenterology, Volume one, 4th edition, 2003 Editor Tadataka Yamada, Lippincott Williams and Wilkins, page 1418).

## Increases metabolic rate
Clinical trials conducted by the University of Geneva in Switzerland indicate that green tea raises metabolic rates and speeds up fat oxidation. In addition to caffeine, green tea contains catechin polyphenols that raise thermogenesis (the rate at which calories are burned), 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 (but not black tea or oolong tea) may help prevent diabetes, although it is worth noting that this is evidence of an association, and that future studies are needed to confirm the effect.

## Boosts immune system and mental alertness
The amino acid L-theanine, found almost exclusively in the tea plant, actively alters the attention networks of the brain, according to results of human trials announced in September 2007. John Foxe, Ph.D., professor of neuroscience, biology and psychology at City College of the City University of New York, found 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. 
On 21 April 2003 the Brigham and Women's Hospital 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.

## 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
-ther tested beverages. This is probably due to the effect of EGEC,
which passed through the Blood-brain barrier.

## Lowers stress hormone levels
According to a study by UCL researchers published in the journal Psychopharmacology, drinking black tea has an effect on stress hormone levels in the body and thus helps in recovering more quickly from life's stresses. The study showed that, 50 minutes after a high stress event, subjects who drank 4 cups of black tea per day for a 4 week period experienced an average cortisol drop of 47%, compared to 27% for the placebo group. Blood platelet activation, which is linked to blood clotting and the risk of heart attacks was also lower in the tea drinker's group.

## Effects on HIV
A recent study appearing in the Journal of Allergy and Clinical Immunology stated that epigallocatechin gallate (EGCG) found in Green Tea can help to boost one's immune system, therefore helping to prevent HIV.  University of Sheffield Research Professor Mike Williamson stated that, "Our research shows that drinking green tea could reduce the risk of becoming infected by HIV, and could also slow down the spread of HIV" however was quick to point out 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" as well as the fact that the research is in very early stages.
Black tea compounds, however, has been shown to be even more effective than EGCG, especially Theaflavins and Thearubigins, which bind to HIV's gp41, which unlike gp120, can't be shed easily by HIV.  However, far less research has been conducted on black tea compounds as compared to green tea, probably related to reasons of profit.   Theaflavins are not found in green tea, but are closely related to EGCG.

## Effects on Inflammatory Bowel Disease (IBD)
The polyphenols in green tea show an ability to inhibit intestinal inflammation in the IL-2 knock-out mouse model of IBD. This is an important possibility for treating IBD, which relate to the polyphenol fraction on NF-k B. EGCG interrupts the proinfammatory cascade by inhibiting the effects of inflammatory mediators on NF-k B by inhibiting the phosphorylation of Ik B by Ik B kinase (IKK). NF-k D cannot migrate to the nucleus and bind with cytokine promoter sequences when bound to Ik B. (Reference: Textbook of Gastroenterology, Volume one, 4th edition, 2003 Editor Tadataka Yamada, Lippincott Williams and Wilkins, pages 1141-1142).

### EGCG Specific mechanism
EGCG does this by competing for gp120 binding sites with HIV, and also protects the brain, which modern anti-retrovirals medicines cannot do, since they can't pass the blood brain barrier.  This is one reason why HIV can never be eliminated as modern medicines can't penetrate the testes, brain, and kupffer cells of the liver, where HIV regroups.  Both green and black tea compounds do penetrate the blood brain barrier.  It has been shown clinically that EGCG and closely related black tea theaflavins have protective effects on many types of dementia, including AIDS related.  EGCG particularly has been shown to deactivate HIV related toxins in vitro that are found in the infected brain.   EGCG is also intereferes with other stages of HIV replication, including HIV protease.

### Oxalates
Oxalates, including those found in all teas are a mixed bag (see problems below), oxalates help with HIV and in general infections by mopping up free iron, one less thing for the immune system to do.  Oxalates chelate zinc as well, a crucial nutrient for HIV to hijack a cell, as it has zinc fingers.

## Effects on bad breath
Researchers at the University of Chicago stated that polyphenols 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 haemochromatosis due to its high content of tannin which limits 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 disease and a temporary increase in short term memory.

# Potential drawbacks

## Effects of fluoride
All tea leaves contain fluoride, however the mature, old tea leaves contain more fluoride, as much as 10-20 times of the fluoride levels in the young leaves of the same tea plant. In general, the level of fluoride in tea is inversely related to the EGCG contents. The more natural EGCG in the tea leaves, the less fluoride. White tea contains less fluoride than green tea and black tea, because it's made of buds and young leaves only.
According to Andreas Schuld of the Canadian "Parents of Fluoride Poisoned Children" tea is very high in fluoride content, much higher than the Maximum Contaminant Level (MCL) set for fluoride in drinking water. Decaffeinated teas have an even higher fluoride content as compared to their caffeinated counterparts. It is thought that this is due to the high fluoride content in the water involved in the de-caffeination process. According to him, fluoride could possibly reduce the anti-cancer properties of tea, or even cause cancer as fluoride is considered a cancer promotor. For instance, he mentions a 1998 study which found positive correlation between colon cancer and tea intake. The high fluoride content could also cause neurological and renal damage, especially in the presence of aluminum. Additionally, the high fluoride content could cause osteoporosis, arthritis, and other bone disorders.
The fluoride content of tea depends directly on soil and air pollution with this contaminant; the danger lies in the fact that the plant absorbs this element at a greater rate than other plants. Care in the choice of the location where the plant is grown is bound to eliminate the risk. Cancers of the digestive tract, which have a higher incidence in Far East countries, have manifold environmental causes and cannot be blamed solely in those peoples' habit of consuming tea.

## Effects associated with caffeine
Caffeine is an addictive substance and overuse of tea can result in harmful side-effects such as an increased likelihood of certain sleep disorders. Decaffeination reduces total catechins in both black and green dry teas by about 15 times and 3 times respectively.

## Oxalates
Tea contains oxalate, overconsumption of which can cause kidney damage, as well as soak up free calcium in the body; other minerals could be soaked up as well.

# United States FDA
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.

# Effect of milk on tea
A study at the Charite Hospital 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 also binds the tannin in the tea, rendering it harmless.