Green tea: Uses. Dosage
Clinical Use
Evidence is largely based on epidemiological studies with few clinical studies available.
CANCER PREVENTION
Epidemiological studies have generally shown a decreased occurrence of cancer in those individuals who drink green tea regularly, although this has not been observed in all studies. A 2003 prospective cohort study using 13-year follow-up data found increased green tea consumption was associated with an apparent delay of cancer onset and death, and all cause deaths. A phase 2 RCT evaluated the effects of green tea on oxidative DNA damage in 143 heavy smokers over 4 months and found a significant reduction in damage as evaluated from urine and plasma. A small, controlled, pilot study concluded with similar results when cells from the oral mucosa of smokers showed much less oxidative damage when compared with controls. These trials indicate that green tea may be effective in reducing cancer in smokers, but much larger trials are needed. In contrast, a 2001 prospective study in Japan found no association between green tea consumption and cancer incidence.
CANCER TREATMENT
Overall, the current evidence does not support the use of green tea as a cancer treatment; however, there are some exceptions, which suggest an adjunctive role. Green tea increased the survival rate of patients with epithelial ovarian cancer in a cohort of 309 Chinese women. Most (77.9%) of the women in the treatment group were alive at the 3-year follow-up as compared with 47.9% of the control group.
In a RCT, 90 patients with cervical lesions infected with human papilloma virus were given either a capsule containing 200 mg of (-)-epigallocatechin-3-gallate (EGCG) and/or an ointment containing 200 mg of polyphenon E to be applied daily. There was a 69% responder rate when compared with placebo, with the ointment showing the best effects.
CARDIOVASCULAR PROTECTION
Epidemiological studies suggest that green tea consumption is associated with a reduced risk of cardiovascular disease. A 2000 prospective cohort study of 8552 people in Japan found that those consuming more than 10 cups per day, compared with those consuming fewer than 3 cups, had a decreased relative risk of death from cardiovascular disease. One cross-sectional study involving 1371 men aged over 40 years found that increased green tea consumption was associated with decreased serum concentrations of total cholesterol and triglyceride and an increase in HDL, together with a decrease in LDL- and VLDL-cholesterols.
DENTAL CARIES AND GINGIVITIS
Green tea extract tablets and chewable oral preparations have been investigated for effects on dental plaque formation and gingival health under RCT conditions, overall producing favourable results.
A double-blind study investigated the effects of green tea catechins and polyphenols on the gingiva when used in the form of chewable oral sweets. Compared with placebo, the green tea product chewed eight times a day significantly decreased gingival inflammation and improved periodontal structures before the 21-day test period was complete.
Another study investigated Chinese green tea polyphenol tablets for effects on plaque formation in 1 50 volunteers. The randomised, controlled crossover study showed that green tea polyphenol tablets used for 2 weeks were able to reduce the plaque index compared with placebo treatment.
SUNBURN PROTECTION
More than 150 in vitro and in vivo studies have reported the benefits of green tea for the skin. Many mechanisms appear to be responsible; green tea protects against UV and PUVA-induced carcinogenesis and DNA damage and is a potent antioxidant, antiinflammatory, anticarcinogenic and vulnerary. Research with human volunteers has found that topical application of green tea to skin half an hour before UV exposure protects against the development of sunburn and epidermal damage. The effect is dose dependent and strongest for the epigallocatechin gallateand epicatechin gallate polyphenols.
WEIGHT LOSS
Animal studies have found that green tea consumption reduces food intake, decreases leptin levels and body weight and increases thermogenesis. However, little clinical evidence is available to determine whether similar effects are seen in humans. One open study did find that a green tea extract AR25 (80% ethanolic dry extract standardised at 25% catechins) taken by moderately obese patients resulted in a 4.6% decrease in body weight and 4.5% decrease in waist circumference after 3 months’ treatment. However, a recent double-blind, placebo-controlled parallel trial, with 46 women attempting a weight-loss program over 87 days, showed no difference between the green tea group and the placebo group. Both groups lost the same amount of weight and displayed similar metabolic parameters at the end of the study period.
Other Uses
Green tea has many other uses, based on results of animal or in vitro tests or on the known pharmacological activity of constituents such as tannin and caffeine. Some of these other uses are treatment of diarrhea, Crohn’s disease, dyspepsia and other digestive symptoms, promoting alertness and cognitive performance, reducing symptoms of headache and promoting diuresis.
COLITIS
Animal studies have shown anti-inflammatory activity in colitis.
RENAL FAILURE
Green tea extract blocks the development of cardiac hypertrophy in experimental renal failure and reduces oxidative stress, according to the results of investigation with animal models.
DIABETES
Animal studies have identified that green tea polyphenols reduce serum glucose levels and improve kidney function in diabetes.
Dosage Range
In general, it appears that 8-10 cups of green tea/day are required.
