Diet & Fitness

Drinking tea has been associated with lower risk of metabolic syndrome, and both green and black tea extracts, as well as the green tea catechin epigallocatechin gallate (EGCG), have demonstrated positive effects in people with metabolic syndrome.^31,32 One meta-analysis of six randomized controlled trials involving people with obesity and metabolic syndrome concluded consuming a green tea catechin-rich beverage reduces abdominal fat accumulation and improves metabolic status.³³ A large meta-analysis of studies pooled findings from 16 controlled trials with a combined total of 1,090 participants with obesity and metabolic syndrome. The results showed that, while the evidence for green tea extract is stronger than that for black, both green and black tea extracts help lower blood glucose levels, raise HDL (“good”)-cholesterol levels, and reduce body mass index, but have no impact on blood pressure, triglycerides, or other cholesterol levels.³⁴ Most studies finding beneficial metabolic effects used 600–900 mg of tea catechins per day for at least 12 weeks. It is important to note liver toxicity has been associated with the use of very high doses of green tea extracts.³²

Green tea is a rich source of antioxidant polyphenols called catechins, including the well-studied epigallocatechin gallate (EGCG). Through their anti-inflammatory and antioxidant effects, green tea catechins appear to protect cardiovascular health and improve metabolism in obesity, insulin resistance, and type 2 diabetes.^35,36,37 Green tea consumption has been correlated with lower risk of type 2 diabetes and diabetes-related heart disease.³⁸ In a preliminary trial, 400 mg per day of green tea extract standardized to contain 90% green tea polyphenols and 45% EGCG reduced arterial stiffness in subjects with type 2 diabetes.³⁹ Although a meta-analysis of 17 randomized controlled trials, including a total of 1,133 subjects with various metabolic disorders, found that green tea consumption significantly improves blood glucose control and insulin sensitivity, another meta-analysis of six studies that only included participants with type 2 diabetes or pre-diabetes found no beneficial effects of green tea or green tea extract on insulin resistance or measures of glycemic control.^40,41 Although an effective dose has not been identified, doses providing 800 mg of EGCG or more per day have been linked to liver injury and are not considered safe.⁴²

Green tea has been shown to lower total and LDL-cholesterol levels in a number of randomized controlled trials. Some research further shows green tea can lower blood pressure, promote weight loss, and reduce the risk of cardiovascular events.⁴³ Its benefits on heart health have largely been attributed to its polyphenols, including catechins such as epigallocatechin gallate (EGCG). A meta-analysis of results from 31 randomized controlled trials with a combined total of 3,216 subjects found green tea supplementation reduced total and LDL-cholesterol levels.⁴⁴ In other large meta-analyses, green tea extract was found to reduce total cholesterol levels, as well as triglyceride levels, in type 2 diabetics,⁴⁵ and decrease total and LDL-cholesterol levels in individuals with overweight and obesity.⁴⁶ A research review indicated green tea extract providing 107–856 mg of EGCG could induce significant reductions in LDL-cholesterol levels.⁴⁷ EGCG, with its powerful antioxidant and anti-inflammatory effects, has also been linked to reduced risks of atherosclerosis and heart attack.⁴⁸

 

Intake of three cups or less of green tea daily has been shown not to affect blood triglyceride levels.⁴⁹ Intake of four or more cups per day has been correlated with lower triglyceride levels.⁵⁰ Overall, the evidence is unclear on how much of an effect high levels of intake of green tea has on triglyceride levels.

Green tea contains caffeine and polyphenols known as catechins (such as epigallocatechin gallate, or EGCG), which may work synergistically to support weight loss.⁵¹ Meta-analyses and reviews of multiple randomized controlled trials have found green tea extract has a small positive effect on weight loss and fat loss in people with overweight and obesity.^51,53,54,55 Research shows green tea extracts can inhibit carbohydrate- and fat-digesting enzymes, improve gut microbiome balance, activate normal adipose tissue metabolism, and possibly raise energy expenditure by increasing heat production.^51,57

Green tea (Camellia sinensis) contains polyphenols that have antioxidant and anti-inflammatory activity, and animal and preliminary human studies have suggested that these polyphenols, when given orally or used topically, can protect skin against ultraviolet rays.^56,57,58,59 In a small, controlled human study, topical application of green tea extracts containing from 2.5 to 10% polyphenols significantly reduced the amount of burning from exposure to ultraviolet rays, with the 10% solution exerting greater protective effect.⁶⁰

In a double-blind trial, men with precancerous changes in the prostate received a green tea extract providing 600 mg of catechins per day or a placebo for one year. After one year, prostate cancer had developed in 3.3% of the men receiving the green tea extract and in 30% of those given the placebo, a statistically significant difference.⁶¹ These results suggest that drinking green tea or taking green tea catechins may help prevent prostate cancer in men at high risk of developing the disease.

Green tea has stimulated production of immune cells and has shown anti-bacterial properties in animal studies.^62,63,64 More research is needed to evaluate the effectiveness of green tea in protecting against infection and other immune system-related diseases.

 

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

 

Two components of green tea, the polyphenols epigallocatechin (EGC) and epicatechin gallate (ECG),⁶⁵ are reported to have an antihistamine effect. Some doctors recommend approximately 3 cups of green tea per day or about 3 grams of soluble components providing roughly 240 to 320 mg of polyphenols, although no human trials have studied the effects of green tea in people with hives.

 

Tannin-containing herbs may be helpful to decrease diarrhea during acute flare-ups and have been used for this purpose in traditional medicine. A preliminary trial using isolated tannins in the course of usual drug therapy for Crohn’s disease found them to be more effective for reducing diarrhea than was no additional treatment.⁶⁶ Tannin-containing herbs of potential benefit include agrimony (Agrimonia spp.), green tea, oak, witch hazel, and cranesbill. Use of such herbs should be discontinued before the diarrhea is completely resolved; otherwise the disease may be aggravated.

 

In a double-blind trial, people with leukoplakia took 3 grams per day of a mixture of whole green tea, green tea polyphenols, and green tea pigments orally and also painted the mixture of the tea on their lesions three times per day for six months.⁶⁷ Those in the green tea group had significant improvement in the healing of their lesions.

 

In a preliminary study, women with cervical dysplasia were randomly assigned to receive either 200 mg per day of EGCG—a green tea extract known as (-)-epigallocatechin-3-gallate—200 mg per day of poly E (another green tea extract), or no treatment (control group) for 8 to 12 weeks. More than 50% of the women receiving EGCG or poly E had an improvement in their Pap smear, compared with only 10% of the women in the control group.⁶⁸