Green tea extract is made from the leaves of the Camellia sinensis plant. In Japan and China, tea has been used for thousands of years as a beverage and herbal medicine.It used traditionally for increasing energy, enhancing mental alertness, improving digestion, and relieving headache.
In Ayurvedic and traditional Chinese medicine , this tea has been used to enhance wound healing, slow down bleeding, promote cognitive function, and improve body temperature regulation.
Green tea extract supplements are commonly used for weight loss, mood balance, physical performance, anti-oxidant protection, immune support, anti-aging and as a nootropic aid.
It is a source of caffeine and has been shown to boost metabolism and stimulate fat burning. As a source of the amino acid L-theanine, green tea extract also demonstrates positive effects on stress and emotional balance.
This article will review the bioactive compounds contained in green tea extract, how this supplement works, health benefits, dosages, side effects, and interactions.
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USES GREEN TEA EXTRACT
According to The Tea Spot, “The distinguishing factor that determines whether a tea plant will become white, green, oolong, or black tea is oxidation.”After the leaves are harvested from the trees, they are processed by drying, withering, rolling and heat-treating. This imitates the process of oxidation.
The Tea Spot explains that, “A black tea is fully oxidized, causing it to turn black, while a white tea is barely oxidized at all, thus retaining its soft, silvery down.”
Green tea is said to contain only about 1% caffeine, as compared to roughly 4% in black tea. Because of that, it is often used as a calming, quieting tea and not a stimulating, energizing drink.
Chinese green tea is said to contain about 33 mg of caffeine per 8-ounce serving, and Japanese tea is said to provide 28 mg per cup.
One method for preparing green tea is to place the leaves in purified water and gently boil them for 3 minutes. The leaves are strained out and the tea is consumed.
People use green tea extract orally for various purposes. Some of these uses include:
Cardiovascular disease
Chronic fatigue syndrome (CFS)
Diabetes
Enhancing cognitive performance and mental alertness
Human papillomavirus (HPV)
Hypotension (low blood pressure)
Non-alcoholic fatty liver disease (NAFLD)
Stomach disorders like diarrhea and vomiting
Ulcerative colitis
The NMCD reports that green tea extract is also used for depression, weight loss, osteoporosis, headache, and sunburn.
It is also used for genital warts, perianal warts, cervical dysplasia, Crohn’s disease, Parkinson’s disease, dental caries/cavities, kidney stones, and skin damage.
Green tea is also of interest to researchers for its potential anticancer effects. It has been studied for breast cancer, cervical cancer, prostate cancer, colon cancer, gastric cancer, liver cancer, lung cancer, leukemia, and skin cancer related to ultraviolet (UV) radiation.
Applied topically, it is used:
As a chewable candy for gingivitis
As a compress for tired eyes and headache
As a poultice for under-eye bags
As a wash for athlete’s foot
As a wash for sunburn
To stop tooth socket bleeding
BENEFITS GREEN TEA EXTRACT
Green tea as Likely Effective for genital warts and hyperlipidemia (high blood lipid (fat) levels).
Clinical research suggests that this herbal extract may benefit various other health disorders. Some conditions where promising results have been observed in preliminary research trials include:
Acne
Breast cancer
Cardiovascular disease
Depression
Diabetes
Esophageal cancer
Leukemia
Mental alertness
Prostate cancer
Stress
Weight loss
For these conditions, the clinical research is limited, and sometimes conflicting results exist. More research is needed to determine the therapeutic efficacy of green tea extract for these and any other conditions.
Green tea is rated by the NMCD as Possibly Effective for cervical dysplasia, coronary artery disease (CAD), endometrial cancer, hypertension (high blood pressure), hypotension, oral leukoplakia (white patches in the mouth), ovarian cancer, and Parkinson’s disease. Green tea extract is regulated as a dietary supplement in the United States. The FDA has not approved this plant as a drug to prevent or treat any medical conditions.
HEART HEALTH & CARDIOVASCULAR DISEASE
People who consume tea regularly might have better measures of heart health and lower risk of death from cardiovascular disease.
Epidemiological studies show that general tea consumption is correlated with a lower prevalence of ischemic heart disease. However, it is not known whether this effect is stronger with consumption of black tea or green tea.
In one large human trial evaluating the link between tea drinking and heart health, 40,000 Japanese men and women between 40 and 70 years of age were monitored for 11 years.
The results showed that drinking at least 5 cups of green tea daily significantly reduced risk of mortality from all causes, but especially from cardiovascular disease. This was in comparison to those who drank less than 1 cup of tea daily.
The polyphenol catechins in green tea extract are believed to support cellular health in general, but especially the cells of the heart and blood vessels.
In 2011, a meta-review found that routine consumption of green tea was associated with modest yet significant reductions in low density lipoprotein cholesterol (LDL-C).
LDL-C is considered to be the “bad” type of cholesterol because it contributes to the formation of arterial plaques which can lead to atherosclerosis (“hardening” and narrowing of the arteries due to plaque) and other cardiovascular disease.
According to the American Heart Association, drinking green tea regularly is associated with reduced risk for stroke. Japanese researchers also found that adding the tea to your daily diet may help to reduce risk for stroke.
At this time the research has largely been positive, with population studies showing benefits for cardiovascular health associated with green tea consumption. The NMCD rates green tea as Possibly Effective for cardiovascular disease.
However more research is needed to determine the therapeutic efficacy of green tea for general heart health. The FDA has not approved this supplement as a drug to prevent or treat cardiovascular disease.
If you are interested in taking green tea extract for cardiovascular health then you should talk about it with your cardiologist or other primary health care provider.
There are side effects and interactions possible that you should be aware of before beginning to use green tea, especially if you have existing cardiovascular disease.
GREEN TEA FOR CANCER
The polyphenol catechins in green tea have been observed in in vitro (cultured cell) and animal studies to have various anticancer effects.
Researchers have observed antioxidant effects and antimutagenic effects (prevent mutations). Compounds in green tea has also been found to inhibit tumor cell proliferation and induce cancer cell apoptosis (cell death).
The National Cancer Institute states that tea polyphenols are known to slow down tumor growth in cells studies and in animal research. This supplement may also provide protection to skin cells against UVB ultraviolet radiation.
The NMCD reports that in humans, green tea has been observed to reduce damage done to DNA in lymphocytes, possibly through antioxidant activity and the activity of DNA repair enzymes.
In some countries where people generally consume a lot of tea, overall cancer rates seem to be lower. However, there is no way to attribute those effects to tea drinking alone.
According to Medical News Today (MNT), in human research trials green tea extract has shown positive impacts on breast, bladder, colorectal, ovarian, throat, liver, lung, prostate, skin, and stomach cancer.
It is hypothesized that the high levels of catechins in the tea are responsible for the anticancer effects seen in these trials. However, the precise mechanisms of action involved are still being investigated.
While there have been many studies showing positive benefits, various other studies have not found any benefits for cancer prevention or recurrence from using green tea extract.
The US FDA states that, currently, there is not enough reliable evidence that substantiates claims of reduced cancer risk from consuming green tea. More research is still needed to determine the therapeutic efficacy for cancer.
WEIGHT LOSS
Green tea supplements are commonly used for aiding weight loss results. As a stimulant, it may boost energy levels, increase metabolism and help to suppress appetite.
The results from human trials are mixed, although benefits have been observed in some trials.
Preliminary clinical research show that green tea extract may increase fat and calorie metabolism due to the caffeine, catechins, and L-theanine content.
Resting energy expenditure and cellular thermogenesis (heat production) have been shown to increase following caffeine consumption.
Studies using specific green tea extract products have demonstrated weight loss effects in overweight and obese patients. Many of these products contain combinations of multiple fat-burning ingredients.
According to MNT, “Green tea may promote a small, non-significant weight loss in overweight and obese adults; however, since weight loss in the studies was so minimal, it is unlikely that green tea is clinically important for weight loss.”
GREEN TEA EXTRACT DOSAGE
The effects of green tea extract catechins are known to be dose-dependent, meaning that higher dosages of catechins induce stronger effects.
In human studies, significant effects typically occur only at high doses. Products containing the equivalent of 400-500 mg EGCG daily have been studied. The majority of green tea supplements contain about 50% EGCG.
Some green tea dosages that have been used in research studies include:
Breast cancer: 3 sups or more tea per day
Hyperlipidemia: 150-2500 mg catechins per day for up to 24 weeks
Mental alertness: 720 mg two times per day for 16 weeks
Obesity: 870 mg catechins two times per day for 8 weeks
Prostate cancer: 200 mg catechins three times per day for one year
Stress: 300 mg extract for 7 days
In human studies, significant effects typically occur only at high doses. Products containing the equivalent of 400-500 mg EGCG daily have been studied. The majority of green tea supplements contain about 50% EGCG.
Some green tea dosages that have been used in research studies include:
Breast cancer: 3 sups or more tea per day
Hyperlipidemia: 150-2500 mg catechins per day for up to 24 weeks
Mental alertness: 720 mg two times per day for 16 weeks
Obesity: 870 mg catechins two times per day for 8 weeks
Prostate cancer: 200 mg catechins three times per day for one year
Stress: 300 mg extract for 7 days
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