Green tea has been used in traditional Chinese medicine for centuries to treat everything from headaches to depression.
The leaves are supposedly richer in antioxidants than other types of tea because of the way they are processed.
All types of tea (green, black and oolong) are produced from the Camellia sinensis plant using different methods. Fresh leaves from the plant are steamed to produce green tea, while the leaves of black tea and oolong involve fermentation.
Green tea is alleged to boost weight loss, reduce cholesterol, combat cardiovascular disease, and prevent cancer and Alzheimer's disease.
We've teamed up with the British Dietetic Association (BDA) to examine whether the myriad health claims about green tea are supported by the evidence.
Green tea contains B vitamins, folate (naturally occurring folic acid), manganese, potassium, magnesium, caffeine and other antioxidants (notably catechins)
The evidence
Cancer
There is no evidence that drinking green tea protects against different types of cancer. A good quality study from 2009 reviewed 51 studies involving more than 1.6 million participants. The studies looked for an association between drinking green tea and cancers of the bowel, prostate, breasts, mouth and lungs. The authors of the review concluded that the evidence of a link between green tea and cancer was weak and "highly contradictory".
Weight loss
It is thought that the antioxidants catechins and caffeine in green tea may have a role in helping the body burn more calories – sometimes referred to as speeding up the metabolism – which can help weight loss. Green tea preparations used for losing weight are extracts of green tea that contain a higher concentration of catechins and caffeine than the typical green tea beverage prepared from a tea bag and boiling water. A well-conducted review from 2012 of 18 studies involving 1,945 people found no significant effect of drinking green tea on weight loss.
Cholesterol
There is increasing evidence that both green and black tea are beneficial for cardiovascular disease prevention. A good quality review from 2013 of 11 studies involving 821 people found that daily consumption of green and black tea (as a drink or a capsule) could help lower cholesterol and blood pressure thanks to tea and its catechins. The authors of the review caution that most of the trials were short term and more good quality long-term trials are needed to back up their findings.
Another good quality review from 2011 found that drinking green tea enriched with catechins led to a small reduction in cholesterol, a main cause of heart disease and stroke. However, it's still not clear from the evidence how much green tea we'd need to drink to see a positive effect on our health, or what the long-term effects of green tea consumption are on our overall health.
Alzheimer's disease
Evidence of a positive link between drinking green tea and Alzheimer's disease is weak. A 2010 laboratory study using animal cells found that a green tea preparation rich in antioxidants protected against the nerve cell death associated with dementia and Alzheimer's disease. Whether these lab results can be reproduced in human trials remains to be seen. As such, the findings do not conclusively show that green tea combats Alzheimer's disease.
The dietitian's verdict
Alison Hornby, a dietitian and BDA spokesperson, says the evidence about green tea's health benefits are inconclusive.
She says: "In the Far East, green tea has been used as a treatment for a variety of conditions ranging from arthritis to weight loss, as well as a preventative measure for diseases such as cancer, although the evidence for the majority of these conditions is weak or lacking.
"However, as a social drink, it appears to be safe in moderate amounts, so lovers of green tea can continue to enjoy it."
Green Tea Side Effects
- Caffeine, which is part of green tea, has an insidious effect that is addictive.
Abuse of strong teas, including green tea, can lead to: insomnia, morning sickness, increased irritability, dizziness and heart palpitations.
- Nursing mothers should be aware that caffeine, which is contained in all tea drinks, can cause insomnia in infants.
- Excessive drinking of strong green tea can cause sleep disorders in adults.
How Much Green Tea Should You Drink?
Some studies recommend 2-3 teacups (not mugs) a day to be beneficial to health. However, consuming up to 5 teacups a day has been shown to lower stomach cancer risk. For weight loss, the best results have been revealed with drinking 7 cups a day. Drinking 10 cups is thought to be the upper limit.
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