Green tea, originally from China and India, has been consumed and hailed globally for its health benefits for centuries, but has only recently gained popularity in the USA.
Behind water tea is the world’s most consumed beverage. However, 78% of the worldwide tea consumed is black and only about 20% is green.
All types of tea are brewed from the dried leaves of the Camellia sinensis bush, except for herbal teas. The type of tea is determined by the oxidation level of the leaves.
Green tea is made from unoxidized leaves and is one of the less processed types of tea. So it contains the most antioxidants and the most beneficial polyphenols.
Important facts about green tea
Here are a few key points about green tea. The main article includes more descriptions and supporting information.
- green tea has been used in traditional Indian and Chinese medicine
- there are many different types of green tea available
- green tea may help prevent a range of ailments including cancer
- more research is needed to prove many of the health claims surrounding green tea
Possible health benefits linked to green tea are listed below. In traditional Chinese and Indian medicine, green tea has been used to manage bleeding and heal wounds, help digestion, enhance heart and mental health , and regulate body temperature.
It is important to note that more evidence is needed before these possible links to health benefits are definitively proved:
1) Green tea and cancer prevention
The polyphenols in tea have been shown to decrease tumor growth in laboratory and animal studies, and can protect against damage from ultraviolet UVB radiation, according to the National Cancer Institute.
In countries where the consumption of green tea is high, cancer rates tend to be lower, but it is impossible to be sure whether it is the green tea that prevents cancer in these particular populations or other factors in the lifestyle.
Some studies have also revealed the positive impact of green tea on the following cancer types:
- colorectal (bowel)
- esophageal (throat)
Researchers claim it is the high level of polyphenols in tea that helps kill and stop cancerous cells from developing. However it is unclear the exact mechanisms by which tea interacts with cancer cells.
Other studies have not found however that tea can reduce the risk of cancer. The amount of tea required to prevent cancer also varies widely in the studies – from 2-10 cups a day.
The Food and Drug Administration ( FDA) stated in 2005 that “there is no credible evidence to support qualified health claims for green tea consumption and a reduced risk of gastric, lung, colon / rectal, esophageal, pancreatic, ovarian, and combined cancers.”
2) Green tea heart benefits
A 2006 study published in the American Medical Association Journal concluded that consumption of green tea is associated with reduced mortality due to all causes, including cardiovascular disease.
For 11 years , starting in 1994, the study followed over 40,000 Japanese participants aged 40 to 79.
Participants drinking at least five cups of green tea a day had a significantly lower risk of dying (especially from cardiovascular disease) than those drinking less than one cup of tea a day.
3) Green tea and lower cholesterol
4) Stroke risk and green tea
The study’s lead author, Dr. Yoshihiro Kokubo, Ph.D., said, “This is the first large-scale study to examine the combined impact of both green tea and coffee on the risk of stroke. You could make a small yet meaningful lifestyle change to help reduce the risk of stroke by adding green tea to your diet every day.
5) Green tea for type 2 diabetes
Studies of the connection between green tea and diabetes were inconsistent. Some have shown a lower risk of developing type 2 diabetes for green tea drinkers compared to those who did not consume tea, while other studies found no association between tea consumption and diabetes.
6) Green tea and weight loss
Green tea may encourage a low, non-significant weight loss in overweight and obese adults; however, as the weight loss was so limited in the studies, green tea is unlikely to be clinically essential for weight loss.
7) Green tea and inflammatory skin diseases
A 2007 study concluded that green tea as a new treatment for skin disorders such as psoriasis and dandruff might hold promise. Researchers have studied an animal model for inflammatory skin diseases, often characterized by dry, red, flaky skin patches caused by inflammation and skin cell overproduction. Those treated with green tea showed slower skin cell growth and the presence of a gene which regulates the life cycles of the cells.
8) Working memory and the effects of green tea
Research published in the journal Psychopharmacology suggests green tea can enhance the cognitive functions of our brain , especially the working memory.
The research team said their findings suggest that green tea in the treatment of cognitive impairments associated with neuropsychiatric disorders such as dementia could be promising.
9) Green tea and Alzheimer’s
In a 2011 study , researchers tested the effect of a green tea component, CAGTE (or “colon available” green tea extract), after it had been digested, to see how it affected a key protein in alzheimer’s disease.
The Alzheimer’s Society commented that “this study adds to past research suggesting that green tea could help reduce the risk of Alzheimer’s disease. The researchers, however, used a much higher dose of the active green tea chemical than would ever have been found in the human body. More work is required to see if green tea at a much lower dose is safe, and to understand the mechanism involved.
Further research is needed to firm up these theories.
Nutritional breakdown of green tea
A zero calorie beverage is unsweetened brewed green tea. The caffeine in a cup of tea will differ depending on the length of time the tea is infused and the amount of tea infused. In general, green tea contains a relatively small amount of caffeine (around 20-45 mg/8 ounce cup) compared to black tea, which contains about 50 mg and 95 mg / cup coffee.
Green tea is considered one of the healthiest drinks in the world and contains one of the highest quantities of antioxidants of any tea. Natural chemicals in tea called polyphenols are believed to have the anti-inflammatory and anti-carcinogenic effects. Green tea is approximately 20-45 percent polyphenols by weight, of which 60-80 percent are catechins such as EGCG. Catechins are antioxidants which are said to help prevent damage to the cells.
Types of green tea
Green tea is available in many types, including:
- bottled and sweetened with sugar or an artificial sweetener
- in single tea bags
- as loose-leaf
- in instant-powder
- green tea supplements, which are sold in capsule form or liquid extracts
Bottled teas are not equivalent to brewed teas, as some 16 ounce bottled teas may contain fewer polyphenols than one cup of brewed tea, according to the 2010 research presented at the American Chemical Society.
Green tea side effects and risks
Drinking green tea for adults has little to no known side effects or contraindications. However it should be made clear the following risks or complications:
- Caffeine sensitivity – those with severe caffeine sensitivities could experience insomnia, anxiety, irritability, nausea, or upset stomach.
- Blood thinners – those taking blood thinners (anticoagulant drugs) such as Coumadin/warfarin should drink green tea with caution due to its vitamin K content. It’s also recommended to avoid green tea and aspirin, because they both reduce the clotting effectiveness of platelets.
- Other stimulants – if taken with stimulant drugs, green tea could increase blood pressure and heart rate.
Green tea supplements contain high levels of active substances which can cause side effects and interact with other herbs, supplements, or medications.
Green tea supplements are unregulated by the FDA and may also contain other substances that are unsafe for health or have unproven benefits for health. Always check with a doctor before starting any herb or supplement regimen.
In particular, pregnant or breastfeeding women, those with heart issues or high blood pressure, issues with the kidney or liver, stomach ulcers or anxiety disorders should not take supplements or extracts from green tea.