Source Tea Advisory Panel 

Introduction

Tea is a drink that is enjoyed by people across the globe. Black tea represents approximately 72% of total consumed tea in the world, whereas green tea accounts for approximately 26%.[1]

Both green tea and black tea come from the leaves of the plant Camellia sinensis, however the processing that the leaves undergo to make the final tea is different. The leaves for black tea are fully oxidised while those for green teas are lightly steamed before being dried.                                      

Black teas mostly come from plantations in Africa, India, Sri Lanka and Indonesia while green teas come from countries in the Far East such as China and Japan.

 Black and green teas both contain similar amount of flavonoids, however they differ in their chemical structure. Green teas contain more of the simple flavonoids called catechins, while the oxidisation that the leaves undergo to make black tea converts these simple flavonoids to the more complex varieties called theaflavins and thearubigins. Figure 2 provides the chemical structures of the major flavonoids found in both green and black tea.

 Tables 1 and 2 provides average values for the different constituents present in green and black tea although they will differ dependent on the variety of leaf, growing environment, manufacturing, particle size of ground tea leaves and infusion preparation.[3]^,[4]

 Table 1 – Principle components of black tea[5]

	Black Tea (% weight of extract solids)
Catechins	3-10
Theaflavins	3-6
Thearubigens	12-18
Flavonols	6-8
Phenolic acids and depsides	10-12
Amino Acids	13-15
Methylxanthines	8-11
Carbohydrates	15
Protein	1
Mineral water	10
Volatiles	<0.1

 

Table 1 – Principle components of green tea⁵

	Green Tea (% weight of extract solids)
Catechins	30-42
Flavonols	5-10
Other flavonoids	2-4
Theogallin	2-3
Other depsides	1
Ascorbic Acid	1-2
Gallic Acid	0.5
Quinic acid	2
Other organic acids	4-5
Theanine	4-6
Other amino acids	4-6
Methylxanthines	7-9
Carbohydrates	10-15
Minerals	6-8
Volatiles	0.02

 

Oolong tea, is a partially fermented leaf, with a flavonoid profile midway between green and black tea.

The health benefits of flavonoids

Although the oxidisation process modifies the type of flavonoids present, the total level and their overall antioxidant activity, is similar in both teas.[6]^,[7] Research is now suggesting that antioxidants, such as those found in both green and black tea, may have a protective role to play in certain conditions such as heart disease, stroke and some cancers.

Further work is still required in understanding the protective antioxidant action of black and green teas. In one in vitro study, black tea was found to be more efficient than green tea as a chemopreventor against certain free radicals, oxygen and nitrogen species.[8] However, in another study both green tea and black tea were equally able to protect against Nitric Oxide toxicity.[9

More detailed information about the health benefits of black tea, antioxidants and flavonoids can be found in the Fact Sheets ‘Tea and Antioxidant Properties; Tea and Cancer; Tea and Cardiovascular Disease’.

The health benefits of green tea

A number of epidemiological studies have suggested that green tea maybe protective against certain types of cancer[10]^,[11] including lung[12], ovarian[13], breast[14]^,[15],[16], prostate[17], stomach cancer[18]^{,[19],[20],[21],[22],[23],[24],[25],[26],[27]} and its precancerous condition, gastritis^18,[28]. The possible protective action of green tea is unclear, although a number of in vitro and animal studies are attempting to explain this.[29]^,[30] Mechanisms by which green tea may be protective are discussed in more detail in the fact sheet ‘Tea and Cancer.’

In addition to its potential anticarcinogenic and antioxidant effects, other studies have shown green tea to have anti-inflammatory, antithrombotic[31], cholesterol lowering[32]^{,[33],[34],[35]}, antiviral and antibacterial properties[36]^,[37],[38].

Although the scientific evidence demonstrating the health benefits of green tea is increasing it is not yet conclusive and provides an interesting area for future research.

Green tea and skin protection

A number of animal studies have shown that topical treatment or oral consumption of green tea polyphenols prevent UVB-induced inflammatory responses, immunosuppression and oxidative stress, which are the biomarkers of several skin disease states[39]. Treatment of green tea polyphenols to skin has been shown to have a beneficial effect on the biochemical pathways involved in skin inflammation, cell proliferation and chemical tumour promoters. Antioxidant and anti-inflammatory effects of green tea have also been observed in human skin.³⁹ One human model found that topical application of green tea polyphenols protected against UV light induced DNA damage[40].  Based on results mainly from animal studies, many companies are now supplementing their skin care products with green tea extracts. However, the effects on human skin are still not well understood and further research in this field is required.

Green tea extract and weight loss

Preliminary research published in the American Journal of Clinical Nutrition suggests that an extract from green tea may help with weight loss by speeding up fat oxidation.[41] In this study, researchers conducted a 6 week study of 10 healthy men in their 20’s and found that those men who were given a green tea extract used more calories in a day than those who did not. However, due to the short term duration of the study, the impact of these results on body composition and body weight could not be determined.

Another study examined whether green tea had any affect on weight maintenance in subjects who had previously lost weight. A total of 104 overweight and moderately obese male and female subjects participated. The study consisted of a very-low-energy diet intervention of 4 weeks followed by a weight-maintenance period of 13 weeks in which the subjects received green tea or placebo. The green tea contained caffeine (104 mg/d) and catechins (573 mg/d, of which 323 mg was epigallocatechin gallate). Green tea appeared to have no effect on weight maintenance following weight loss on the low energy diet compared to the placebo.[42]

Further research using longer term studies is required before any firm conclusions about green tea and weight loss can be drawn.

Caffeine Content of Green Tea and Black Tea

Black and Green teas are produced from the same plant Camellia sinensis so both green and black teas naturally contain caffeine. Further information about caffeine and tea can be found in the Fact Sheet, ‘Tea and Caffeine.’

Which to drink?

The health benefits gained from drinking black and green tea are comparable, both helping towards promoting health and well-being. The decision about which to drink is simply a matter of taste.

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References:

[1] Katiyar SK et al (1996) Tea in chemoprevention of cancer: epidemiological and experimental studies. Int J Oncol 8:221-238

[2] McKay DL, and Blumberg JB (2002) The Role of Tea in Human Health: An Update JACN 21:1-13

[3] Wang H, at al (2001) Determination of flavonols in green and black tea leaves and green tea infusions by high performance liquid chromatography. Food Research International 34; 2-3: 223-227

[4] Astill C, et al (2001) Factors affecting the caffeine and poyphenol contents of black and green tea infusions. J Agric Food Chem 49 (11): 5340-7

[5] Harold N, Graham PD (1992). Green tea composition, consumption and polyphenol chemistry. Prev Med 21: 334-50

[6] Leung LK, et al (2001) Theaflavins in black tea and catechins in green tea are equally effective antioxidants. J Nutr 131(9); 2248-51

[7] Luczaj W, Skrzydlewska E (2005) Antioxidative properties of black tea. Prev Med 40; 910-918

[8] Paquay JB, et al (2001) Protection against nitric oxide toxicity by tea. J Agric Food Chem 48(11): 5768-5772

[9] Sarkar A, et al (2001) Black tea is a powerful chemopreventor of reactive oxygen and nitrogen species: comparison with its individual catechin constituents in green tea. Biochem. Biophyss. Res. Commun 284 (1): 173-178

[10] Nakachi K, et al (2000). Preventative effects of drinking green tea on cancer and cardiovascular disease: epidemiological evidence for multiple targeting prevention. Biofactors 13(1-4): 49-54

[11] Imai K, et al (1997) Cancer preventative effects of drinking green tea among a Japanese population. Prev Med 26; 769-75

[12] Zhong L, et al (2001) A population-based case-control study of lung cancer and green tea consumption among women living in Shanghai, China. Epidemiology 12(6): 695-700

[13] Zhang, M., C.W. Binns & A.H. Lee (2002) Tea consumption and ovarian cancer risk: a case-control study in China. Cancer Epidemiol Biomarkers Prev 11; 713-718

[14] Wu, A.H., M.C. Yu, C.C. Tseng, J. Hankin & M.C. Pike (2003) Green tea and risk of breast cancer in Asian Americans. Int J Cancer 106; 574-579

[15] Nakachi, K., K. Suemasu, K. Suga, T. Takeo, K. Imai & Y. Higashi (1998) Influence of drinking green tea on breast cancer malignancy among Japanese patients. Jpn J Cancer Res 89; 254-261

[16] Inoue, M., K. Tajima, M. Mizutani, H. Iwata, T. Iwase, S. Miura, K. Hirose, N. Hamajima & S. Tominaga (2001) Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. Cancer Lett 167; 175-182

[17] Jian L, et al (2004) Protective effect of green tea against prostate cancer; a case-control study in southeast China. Int J Canc 108(1);130-5

[18]Setiawan V, et al  (2001) Protective Effect of green tea on the risks of chronic gastritis and stomach cancer. Int J Cancer 92; 600-604

[19] Yu GP, et al (1995) Green tea consumption and risk of stomach cancer: a population based case-control study in Shanghai. Cancer Causes Control 6; 532-8

[20] Ji BT, et al (1996) The influence of cigarette smoking, alcohol and green tea consumption on the risk of carcinoma of the cardia and distal stomach in Shanghai, China. Cancer 77: 2449-57

[21] Inoue M, et al (1998) Tea and coffee consumption and the risk of digestive tract cancers: data from a comparative case-reference study in Japan. Cancer Causes Control 9; 209-16

[22] Kono S, et al (1988) A case-control study of gastric cancer and diet in Northern Kyushu, Japan. Jpn J Cancer Res 79; 1067-74

[23] Yu GP, et al (1991) Risk factors for stomach cancer: a population based case-control study in Shanghai. Cancer Causes Control 2; 169-74

[24] Sun, C.L, et al (2002) Urinary tea polyphenols in relation to gastric and esophageal cancers: a prospective study of men in Shanghai, China. Carcinogenesis 23; 1497-1503

[25] Nagano, J, et al (2001) A prospective study of green tea consumption and cancer incidence, Hiroshima and Nagasaki (Japan). Cancer Causes Control 12; 501-508

[26] Tsubono, Y, et al (2001) Green tea and the risk of gastric cancer in Japan. N Engl J Med 344; 632-636

[27] Galanis, D.J., et al (1998) Intakes of selected foods and beverages and the incidence of gastric cancer among the Japanese residents of Hawaii: a prospective study. Int J Epidemiol 27; 173-180

[28] Shibata K, et al (2000) Green tea consumption and chronic atrophic gastritis: a cross sectional study in a green tea production village. J Epidemiol 10(5): 310-6

[29] Chen D, et al (2004) Green tea and tea polyphenols in cancer prevention. Front Biosc 9; 2618-31

[30] Doss MX (2005) Trapping of growth factors by catechins: a possible therapeutical target for prevention of proliferative diseases. J Nutr Biochem 16; 259-266

[31] Kang WS, et al (1999) Antithrombotic activities of green tea catechins and (-)-epigallocatechin gallate. Throm Res 96(3): 229-37

[32] Kono S, et al (1996) Relation of green tea consumption to serum lipids and lipoproteins in Japanese men. J of Epidemiology 6(3): 128-33

[33] Osada K, et al (2001) Tea catechins inhibit cholesterol oxidation accompanying oxidation of low density lipoprotein in vitro. Comp Biochem Physiol C Toxicol Pharmacol 128(2); 153-64  

[34] Kono S, et al (1992) Green tea consumption and serum lipid profiles: a cross-sectional study in northern Kyushu, Japan.  Prev Med, 21(4); 526-31

[35] Erba D, et al (2005) Effectiveness of moderate green tea consumption on antioxidative status and plasma lipid profile in humans. J Nutr Biochem 16; 144-149

[36] Rasheed A, et al (1998) Antibacterial activity of Camellia sinensis extracts against dental caries. Arch Pharm Res, 21(3): 348-52  

[37] Matsunaaga K, et al (2001) Legionella pneumophila replication in macrophages inhibited by selective immunomodulatory effects on cytokine formation by Epigallocatechin Gallate, a major form of tea catechins. Infect Immun; 69(6): 3947-53

[38] Otake S, et al (1991) Anticaries effects of polyphenolic compounds from Japanese green tea. Caries Res, 25(6): 438-43  

[39] Katiyar SK (2003) Skin photoprotection by green tea: antioxidant and immunomodulatory effects. Curr Drug Targets Immune Endocr Metab Disor 3; 234-42

[40] Katiyar SK, et al (2000) Green tea polyphenols treatment to human skin prevents formation of ultraviolet light B-induced pyrimidine dimmers in DNA. Clin Cancer Res 6(10): 3864-9

[41] Dulloo A, et al (1999) Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24 hour energy expenditure and fat oxidation in humans. Am J Clin Nutr 70(6): 1040-1045

[42] Kovacs EMR, et al (2004) Effects of green tea on weight maintenance after body-weight loss

Br J Nutr 91; 431-37