TEA is considered the most consumed beverage in the world behind water, however 78 percent of the tea consumed worldwide is black and only about 20 percent is green.
All types of tea except herbal tea are brewed from the dried leaves of the Camellia sinensis bush. The level of oxidation of the leaves determines the type of tea.
Green tea is made from un-oxidised leaves and is the least processed type of tea and therefore contains the most antioxidants and beneficial polyphenols.
Green tea was used in traditional Chinese and Indian medicine to control bleeding and heal wounds, aid digestion, improve heart and mental health and regulate body temperature.
Recent studies have shown green tea can potentially have positive effects on everything from weight loss to liver disorders to type two diabetes.
This MNT Knowledge Centre feature is part of a collection of articles on the health benefits of popular foods. It provides a nutritional breakdown of green tea and an in-depth look at its possible health benefits the different forms of green tea, and some precautions when consuming green tea.
Nutritional breakdown of green tea
Unsweetened brewed green tea is a zero calorie beverage. The caffeine contained in a cup of tea can vary according to length of infusing time and the amount of tea infused.
In general, green tea contains a relatively small amount of caffeine (approximately 20-45 milligrammes per 8 oz cup), compared with black tea which contains about 50 milligrams and coffee with 95 milligrams per cup.
Green tea is considered one of the world’s healthiest drinks and contains the highest amount of antioxidants of any tea. The natural chemicals called polyphenols in tea are what are thought to provide its anti-inflammatory and anti-carcinogenic effects.
Epigallocatechin-3-gallate (EGCG) is the most studied and bioactive polyphenol in tea and has been shown to be the most effective at eliminating free radicals,1, 4.
Green tea is approximately 20 percent to 45 percent polyphenols by weight, of which 60 percent to 80 percent are catechins such as EGCG.
Possible health benefits of green tea
Below are the potential health benefits associated with green tea:
According to the National Cancer Institute, the polyphenols in tea have been shown to decrease tumor growth in laboratory and animal studies and may protect against damage caused by ultraviolet UVB radiation.
In countries where green tea consumption is high cancer rates tend to be lower, but it is impossible to know for sure whether it is the green tea that prevents cancer in these specific populations or other lifestyle factors.
One large-scale clinical study compared green tea drinkers with non-drinkers and found that those who drank the most tea were less likely to develop pancreatic cancer, particularly women, who were 50 percent less likely to develop the disease.
Studies have also shown the positive impacts of green tea on breast, bladder, ovarian, colorectal, esophageal, lung, prostate, skin and stomach cancer. Researchers believe that it is the high level of polyphenols in tea that help kill cancerous cells and stop them from growing, however, the exact mechanisms by which tea interacts with cancerous cells is unknown.
Other studies have shown a lack of preventative effects of tea on cancer. The amount of tea required for cancer-preventive effects has also varied widely in studies – from 2-10 cups per day.
In 2005, the FDA stated 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.
A 2006 study published in the Journal of the American Medical Association concluded that green tea consumption is associated with reduced mortality due to all causes, including cardiovascular disease.
The study followed over 40 000 Japanese participants between the ages of 40 and 79 for 11 years, starting in 1994.
The participants who drank at least five cups of green tea per day had a significantly lower risk of dying (especially from cardiovascular disease) than those who drank less than one cup of tea per day.
Another study found that consuming 10 cups of green tea per day can lower total cholesterol, however, consuming four cups or less had no effect on cholesterol levels.1
Type 2 Diabetes:
Studies concerning the relationship between green tea and diabetes have been inconsistent. Some have shown a lower risk of developing type 2 diabetes for green tea drinkers than for those who consumed no tea, while other studies have found no association between tea consumption and diabetes at all.1
Green tea may promote a small, non-significant weight loss in overweight and obese adults; however, since the weight lost in the studies were so minimal; it is unlikely that green tea is clinically important for weight loss.
Other studies have found that green tea is helpful in preventing dental cavities and stress. – www.medicalnewstoday.com