Green tea (Camelia sinensis) is valued for the bioflavonoids in its leaves which give off catechins into water when brewed. Green tea enthusiasts say that green tea should be made with water not hotter than 175 degrees F (rather than boiling water) for better flavor and less bitterness. Bioflavonoids are plant pigments that protect plants from UV light and plant diseases. They are valuable in vision and general health due to their powerful antioxidant action and anti-viral qualities. A review of research has noted that there have been many studies connecting green tea catechins to prevention of the kind of diseases that are most often connected to lifestyle, such as cardiovascular disease, diabetes, stroke, and obesity. Scientists are finding that they are also helpful in many conditions not involving lifestyle such as allergies, brain functioning, and menopausal symptoms.
As an antioxidant, green tea catechins, unlike some other antioxidants, appear to be quite readily absorbed into the body. The inability of the body to properly digest many bioflavonoids has been an issue for many researchers as to their antioxidant value. However, researchers found in studies with lab animals that green tea catechins are, in fact, passed from the digestive system into the tissue of the eye.1 Researchers found that green tea epigallocatechin protected lab animal retinas from the oxidative damage of hydrogen peroxide.2 Other researchers have determined that green tea epigallocatechin protects lab animal retinas from damage from ultra-violet B light.3 This protective effect in the case of UV light seems to have to do with the ability of cells to resist degredation when exposed to UV light.4 A protective effect has also been found with respect to degredation due to diabetic retinopathy.5
In a number of studies researchers have found that consumption of green tea extract is associated with weight loss. One study found that rats on normal or high fat diets experienced reduced weight gain and improved glucose tolerance when fed a green tea decoction for 6 weeks.6 Other researchers have determined that the combination of voluntary running and decaffeinated green tea extract in lab animals on high fat diets was beneficial. They found, after 16 weeks, that body mass was reduced 27.1%, visceral fat mass was reduced 36.6%, blood glucose (fasting) was reduced 17%, insulin resistance was reduced 65%. They concluded that the results were due to energy metabolism modulation and reduction of carbohydrates into fat.7
Allergies & Sensitivities
Researchers noted that in a double-blind clinical study on Japanese subjects with pollen allergies, after 11 weeks of green tea consumption (and timed to match the highest point of pollen in the environment) that symptoms of hay fever or pollen allergy were significantly reduced. They even determined that the most effective green tea for this purpose was fully-matured Benifuuki tea, from the second crop season was the most effective!8 Other researchers researched green tea and its effect on allergic dermatitis, finding that the anti-inflammatory results were helpful without increasing skin irritation.9
It has been reported in a number of animal studies that green tea extract combined with the amino acid l-theanine (which is primarily found in green tea) has been quite helpful for cognitive capacity. Researchers looked at the effect on human subjects who had mild cognitive impairment, focusing on attention and memory. Forty five patients and 46 controls aged 48 to 66 were given either the green tea/l-theanine combination or placebo. They determined that there were measurable improvements in memory and selective attention. Brain wave research further indicated an significant increase in theta waves which are known to be indicators of cognitive alertness.10
There have been a number of studies looking at the effect of green tea catechins on conditions for which senior women are most at risk. One study concluded, that through modification of estrogen metabolism, green tea may reduce breast cancer risk.11 Osteopenia, bone density, is a critical factor in the severity of osteoporosis. 171 women with osteopenia who were part of a 6 month study were given placebo, placebo plus a hour of Tai Chi 3 times a week, green tea polyphenols, or green tea polyphonols plus Tai Chi 3 times a week. The researchers found that all of the groups that received the green tea and/or the exercise demonstrated improved bone density measurements and those groups that received the green tea polyphonols benefited the most.12 Green tea has also been found to be helpful for overactive bladder, 13 regulation of glucose and LDL cholesterol,14 and general relief of menopausal symptoms as part of a morning/evening formula combined with other herbs.15
1. Chu et al. Green Tea Catechins and Their Oxidative Protection in the Rat Eye, Journal of Agricultural and Food Chemistry, 2010; 58 (3): 1523
2. Epigallocatechin Gallate (EGCG) Prevents H2O2-Induced Oxidative Stress in Primary Rat Retinal Pigment Epithelial Cells, D. Cia, el al, Current Eye Research, Feb, 2014.
3. Epigallocatechin gallate eye drops protect against ultraviolet B-induced corneal oxidative damage in mice, M.H.Chen, et al, Molecular Vision, Feb. 2014
4. Epigallocatechin-gallate (EGCG) regulates autophagy in human retinal pigment epithelial cells: a potential role for reducing UVB light-induced retinal damage, C.P. Li, et al., Biochemical and Biophysical Research Communication, Sept., 2014
5. Green tea is neuroprotective in diabetic retinopathy, K. C. Silva, et al., Investigative Ophthamology & Visual Science, Feb., 2013.
6. Green tea decoction improves glucose tolerance and reduces weight gain of rats fed normal and high-fat diet., C. Snoussi, Journal of Nutritional Biochemistry, Feb., 2014.
7. Voluntary exercise and green tea enhance the expression of genes related to energy utilization and attenuate metabolic syndrome in high fat fed mice, S. Sae-Tan, et al, Molecular Nutrition & Food Research, Dec., 2013.
8. Human clinical studies of tea polyphenols in allergy or life style-related diseases, M. Maeda-Yamamoto, Current Pharmaceutical Design, 2013.
9. Human skin safety test of green tea cell extracts in condition of allergic contact dermatitis, H.K.Kim, et al, Toxicological Research, June, 2012.
10. A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study, S.K. Park, et al, Journal of Medicinal Food, April, 2011.
11. Green tea intake is associated with urinary estrogen profiles in Japanese-American women, B. J. Fuhrman, et al, Nutrition Journal, Feb, 2013
12. Mitigation of oxidative damage by green tea polyphenols and Tai Chi exercise in postmenopausal women with osteopenia, G. Qian, et al, PLos One, 2012
13. Green tea catechin can improve symptoms of menopause-induced overactive bladder, S. Payton, Nature Reviews. Urology, June, 2012
14. Effect of 2-month controlled green tea intervention on lipoprotein cholesterol, glucose, and hormone levels in healthy postmenopausal women, A. H. Wu, et al, Cancer Prevention Research, March, 2012
15. Morning/evening menopausal formula relieves menopausal symptoms: a pilot study, J. Sun, Journal of Alternative and Complementary Medicine, June, 2003.