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The black tea bioactivity: An overview
Abstract
Tea is one of the most popular beverages in many countries and is the second, after the pure water, most consumed drink in the world, but consumption habit varies between different countries. Incidence of different diseases varies widely across the world and many investigators relate these differences to diet including habitual tea drinking. It is consumed mostly as green tea and black tea where other forms such oolong; red or white teas are less popular. Green tea was extensively investigated on its health benefits but black tea is only now catching the serious attention of scientific community. Compounds contained in black tea such as theaflavins and thearubigens contribute to black tea dark color and distinctive flavor. They also provide health benefits originally attributed solely to green tea. This review summarizes available information on bioactive ingredients of tea, their bioactivity and relation to diseases, bioavailability with special attention to health benefits of black tea.
... Over the years tea has become a hot topic of research due to its nutritional and therapeutic properties as tea contains a diverse group of bioactive compounds which are not only bio-stable but are direct-acting than any other component of other medicinal plants thus they hold the potentiality of being a therapeutic drug in the future scenario. Coming to the bioactive components of tea, fresh tea leaves are enriched in polyphenolic compounds comprising 36% of the total weight next to them come carbohydrate (25%), proteins (15%), amino acids (4%), and various inorganic elements [18]. The major and characteristic polyphenols of tea involve flavanols of which catechins are pre-dominant of which (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC), (-)-epigallocatechin gallate (EGCG), (+)-catechin (C), and (+)gallocatechin (GC) are the important ones [19,20]. ...
... Depending on the variation in the processing technique for the production of commercial tea the metabolites of different tea varies. The oxidation process plays a crucial role in the variation of metabolites as fresh tea leaves contains a significant amount of polyphenolic compounds (simple and complex polyphenols), 25% carbohydrates (pectins, glucose, fructose, cellulose), 15% proteins, 6.5% lignin, 5% minerals, and trace elements (magnesium, chromium, iron, copper, zinc, sodium, cobalt, potassium, etc.), 4% amino acids (such as theanine [5-N-ethyl-glutamine], glutamic acid, tryptophan, aspartic acid), 2% lipids, 1.5% organic acids, 0.5% chlorophyll as well as carotenoids [18] whereas a typical tea beverage containing 2.5 g of processed tea leaves brewed for 3 minutes in 250 ml hot water, usually contains 620-880 mg of different water-extractable solids [25]. The major constituents of tea biomolecules belong to the polyphenol group which mainly include six groups of compounds that remains the same for green tea black tea and oolong tea, such as phenolic acids (PA), flavones, flavonols, anthocyanins, flavanols, and hydroxyl-4 flavanols among which the most important tea polyphenols are the flavanols of which the flavon-3-ols commonly known as catechins are the predominant one [26]. ...
... The oxidation process commonly known as fermentation is very much different from the actual anaerobic breakdown of energy-rich compounds such as carbohydrates to alcohol or organic acids using microorganisms but is mainly the oxidative polymerization and condensation of the Flavon-3-ols catalyzed by the endogenous polyphenol oxidases [17].The process allows the tea leaves to undergo enzymatic oxidation where the internal polyphenol oxidase causes the polymerization of the flavan-3-ols to catechin oligomers resulting in the formation of bisflavanols and the major two pigments of black tea i.e. theaflavins (TFs) & thearubigins (TRs) accounting for 3-6% and 12-18% of the dry weight of black tea. As a result, the percentage of catechins decreases in black tea and the rest are transformed into TFs & TRs, contributing to the sweet aroma of malt sugar and the dark brown hue of black tea [18]. The group of TFs is mainly comprised of four major TFs and some minor TFs with its related compounds of which the major ones are -Theaflavin(TF), Theaflavin 3-monogallate(TF3G), Theaflavin 3'-monogallate(TF3'G), and Theaflavin3,3'-digallate (TF3,3'DG) and the minor ones are isotheaflavin, neotheaflavin,theaflavic acids and theaflavates [28]. ...
Neurodegenerative diseases involve a heterogeneous group of disorders characterized by progressive impairment and degeneration of nerve structure and function, eventually leading towards the death of certain parts of the CNS and brain. The most common form of neurodegenerative diseases includes Alzheimer's disease (AD) leading towards progressive loss of memory, Parkinson's disease (PD) causing impairment in movements, Huntington's disease (HD) affecting the ability to walk, talk and think. The pathogenesis of these diseases mainly AD and PD are complex and there is no such cure for these diseases as the drugs that are currently in use shown to have an adverse effect on these diseases. However epidemiological studies have shown that consumption of tea has therapeutic effects in treating those neurodegenerative diseases especially the major tea components i.e. Catechins, Caffeine, Theanine, TFs in elderly persons. The major tea components are antioxidants which help to combat oxidative stress, the major reason behind all those neurodegenerative diseases, regulating signaling pathways as well as helps in metal chelation. The objective of this review is to summarize all the available information on different bioactive components of tea in the treatment of different neurodegenerative diseases.
... The processing, origin, taste, colour, and composition of different teas are discussed in Table 1 and Figure 1 (Graham 1992, Belitz and Grosch 1997, Vinson 2000, Sano et al., 2001, Khokhar and Magnusdottir 2002, Chacko et al., 2010, Skotnicka et al., 2011, Dias et al., 2013, Zheng et al., 2015, Ng et al., 2018 and the structure of common chemical components that are responsible for the therapeutic value of teas is represented in Figure 2 and (Hajiaghaalipour et al., 2015) Involves fixation, rolling, yellowing & the process of drying (Zhang et al., 2019) Involves fixation, postfermentation, shaping & the process of drying (Zhang et al., 2019) Origin China (Sinija and Mishra 2008) Asia and Europe (Skotnicka et al., 2011) Fujian Province of China (Zheng et al., 2015) Fujian Province of China (Ning et al., 2016) China China & Japan (Zheng et al., 2015) Taste Bitter (Soni et al., 2015) Distinct taste (Soni et al., 2015) Bitter, sweet, brisk & mellow Mild taste (Hilal and Engelhardt 2007) Caramel flavor (Guo et al., 2019) Mellow taste (Zheng et al., 2015) Colour Green or yellow (Soni et al., 2015) Red to black (Soni et al., 2015) Appear red from the edges & green in the center (Chen et al., 2010) Pale yellow colour (Hilal and Engelhardt 2007) Yellow color Brick red to brown color (Zheng et al., 2015) ...
... The processing, origin, taste, colour, and composition of different teas are discussed in Table 1 and Figure 1 (Graham 1992, Belitz and Grosch 1997, Vinson 2000, Sano et al., 2001, Khokhar and Magnusdottir 2002, Chacko et al., 2010, Skotnicka et al., 2011, Dias et al., 2013, Zheng et al., 2015, Ng et al., 2018 and the structure of common chemical components that are responsible for the therapeutic value of teas is represented in Figure 2 and (Hajiaghaalipour et al., 2015) Involves fixation, rolling, yellowing & the process of drying (Zhang et al., 2019) Involves fixation, postfermentation, shaping & the process of drying (Zhang et al., 2019) Origin China (Sinija and Mishra 2008) Asia and Europe (Skotnicka et al., 2011) Fujian Province of China (Zheng et al., 2015) Fujian Province of China (Ning et al., 2016) China China & Japan (Zheng et al., 2015) Taste Bitter (Soni et al., 2015) Distinct taste (Soni et al., 2015) Bitter, sweet, brisk & mellow Mild taste (Hilal and Engelhardt 2007) Caramel flavor (Guo et al., 2019) Mellow taste (Zheng et al., 2015) Colour Green or yellow (Soni et al., 2015) Red to black (Soni et al., 2015) Appear red from the edges & green in the center (Chen et al., 2010) Pale yellow colour (Hilal and Engelhardt 2007) Yellow color Brick red to brown color (Zheng et al., 2015) ...
The Camellia sinensis plant provides a wide diversity of black, green, oolong, yellow, brick dark, and white tea. Tea is one of the majorly used beverages across the globe, succeeds only in the water for fitness and pleasure. Generally, green tea has been preferred more as compared to other teas due to its main constituent e.g. polyphenols which contribute to various health benefits. The aim of this updated and comprehensive review is to bring together the latest data on the phytochemistry and pharmacological properties of Camellia sinensis and to highlight the therapeutic prospects of the bioactive compounds in this plant so that the full medicinal potential of Camellia sinensis can be realised. A review of published studies on this topic was performed by searching PubMed/MedLine, Scopus, Google scholar, and Web of Science databases from 1999-2022. The results of the analysed studies showed that the main polyphenols of tea are the four prime flavonoids catechins: epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC), and epicatechin (EC) along with the beneficial biological properties of tea for a broad heterogeneity of disorders, including anticancer, neuroprotective, antibacterial, antiviral, antifungal, antiobesity, antidiabetes and antiglaucoma activities. Poor absorption and low bioavailability of bioactive compounds from Camellia sinensis are limiting aspects of their therapeutic use. More human clinical studies and approaching the latest nanoformulation techniques in nanoparticles to transport the target phytochemical compounds to increase therapeutic efficacy are needed in the future.
... [1] Tea sprouts contain a variety of useful substances, including such rare and valuable ones as caffeine, theobromine, theophylline, tannin (catechins), essential oils, and numerous vitamins. [1][2][3][4] Research on the tea biochemistry and tea production in recent years has reached a high level, that allowed us to fully study the biochemical composition of both tea raw materials and tea, which led to an update of ideas about tea and its production. However, the main biochemical parameters vary significantly depending on the tea plant grows area, weather conditions, varieties, agricultural technology, leaf maturity, and many other factors. ...
... [7] The action of vitamin P and vitamin C is related, they are involved in redox processes. Therapeutic effect of vitamin C is much more effective in the presence of vitamin P. Ruthin is better absorbed and retained in the body and more successfully prevents scurvy, when acting together with vitamin C. [4] In the Krasnodar region (and in Russia as a whole), comprehensive fundamental research of the biochemical characteristics of tea and tea raw materials has not been conducted Green Reports Green Rep., 2020, 1(2), 1-4. before at the modern world level. ...
A complete biochemical evaluation of raw materials (3-leaf sprouts) and finished (black, green) tea was performed. The content of the vitamin C by cultivars and forms was from 100 to 148 mg. 100g-1. We determined increase ascorbic acids (AA) from May to August. The plants with a relatively stable content of vitamin C in sprouts are more valuable. Our research show, that during processing raw materials (fresh sprouts) to finished tea, there are significant losses of AA (up to 90%). Studies have shown that depending on the season of tea leaf collection, the content of Ruthin in green tea ranges from 36 mg. 100g-1 to 41 mg. 100g-1 , and in black tea-in the range of 17 mg.100g-1-20 mg.100g-1 , which is lower than in green tea. The content of Ruthin in black and green tea was similar content of ascorbic acid. On average Ruthin in green tea is 3 times more than in black tea. The variation of vitamins in both sprouts and ready-made tea has been established, which is due to both varietal characteristics and the influence of weather conditions of vegetation. Varieties and forms with a high content of ascorbic acid and Ruthin were determined, which increases the nutritional value of the finished beverage. It is important to research the rules about accumulation and distribution of biological substances in tea plants, which will provide scientific ideas about how to control contents and will increase biological active substances in new tea cultivar.
... Since 1947, India has approximately 563,980 hectares of land under tea cultivation and the largest tea cultivating states include Assam (304,400 hectares), West Bengal (140,440 hectares), Tamil Nadu (69,620 hectares) and Kerala (35,010 hectares). The versatile health aspects of tea are already being extensively studied [2,3]. This research article focuses to study the antioxidant, hypoglycemic and hypolipidemic potentials of three different varieties of black tea (Darjeeling tea, Assam tea and Nilgiri tea) grown in three different states of India. ...
Tea is a very popular commercial crop and India is the world's largest consumer of tea in the world and the second largest producer of tea. Black tea is mostly preferred in Indian context and its multifaceted health benefits are being largely explored. This research article made a comparative study of antioxidant, hypoglycemic and hypolipidemic effect of Assam, Darjeeling and Nilgiri varieties of black tea. Research results have shown that Assam variety of tea has the highest antioxidant, hypoglycemic and hypolipidemic potentials followed by Nilgiri and Darjeeling variety.
... Several research report that green tea can act as an inhibitor of herpes virus activity, influenza virus, anticarcinogenic, and cardiovascular disease (CVD) and is antimicrobial as well as suitable for oral health and to prevent colon cancer (de Oliveira et al., 2015;Hajiaghaalipour et al., 2015;Reygaert, 2017;Yang et al., 2014). These health benefits are due to bioactive compounds such as catechins found in green tea (Sharangi et al., 2014;Skotnicka et al., 2011). ...
Fixation is essential in green tea processing to inactivate the polyphenol oxidase enzyme. In Indonesia, green tea is made from the Assam variety and produced using the panning method. Few studies are reported on green tea made from Indonesian clones of the Sinensis variety. This study aims to identify chemical characteristics, antioxidant activity, and sensory evaluation of green tea from local clones of the Sinensis variety (GMBS 2, GMBS 4, and GMBS 5) with different fixation methods (panning and steaming). The results show that the caffeine content of green tea products ranged from 2.51-2.59% and 2.67-2.74% for panning and steaming methods. The panning method produced green tea with higher total polyphenol and flavonoid content than the steaming method. Green tea with the panning method has an IC50 value of 14.45; 14.41; and 17.41 mg/L for GMBS 2, GMBS 4, and GMBS 5, respectively. The panning method resulted in a smaller IC50 value than the steaming method for GMBS 2 and GMBS 4 clones. The steaming method produced green tea with a higher taste, aroma, and total score than those the panning method. However, different fixation methods did not significantly affect the appearance, liquor color, and leaf infusion. In conclusion, different fixation methods on GMBS 2, GMB 4, and GMB 5 produced green tea products that met the Indonesian National Standard 3945:2016. Further research is needed to determine the role of the plucking period/season and the characteristics of volatile compounds of green tea from GMBS clones with different fixation methods.
... Tea (Camellia sinensis) is native to the different Asian countries like China, India, Laos, Thailand, Vietnam, and Myanmar [1]. Tea is one of the most widely consumed beverages in the world, with a global market comprising of four major zones: Asia-Pacific, Europe, North America and Africa [2,3]. The tea is second only to water in terms of worldwide consumption and presently tea is cultivated in over thirty countries around the world [4,5]. ...
p> Black tea has lower antioxidant activity than green tea, the color is slightly darker and less stable during storage. Therefore, it is necessary to add natural antioxidants so that antioxidants increase, and the color is brighter and stable. This study aims to determine the effect of adding lime juice and Eucalyptus globulus essential oil (MEEg) on antioxidant activity and color, as well as organoleptic hedonic brewing of black tea. The research method used was an experimental method consisting of 2 stages, namely the stage of determining the length of brewing black tea and the stage of adding lime juice (0, 1, 2, 3% v/v) and MEEg (0.00, 0.05, 0). ,10, and 0.15% v/v). The results showed that the best brewing time was 8 minutes with an IC<sub>50</sub> value of 1411.24±75.79 ppm, a pH value of 5.25±0.02, a yellow-red color (<sup>o</sup>Hue 75.93±3.16), and a lightness value. 47.09±1.06. The addition of lime juice tends to decrease antioxidant activity, total phenolic, total flavonoid, and total condensed tannins, but the addition of MEEg increases antioxidant activity, total phenolic, total flavonoid, and total condensed tannins in black tea. The addition of lime juice and MEEg increased the preference for the tea color and mint flavor, but decreased the preference for the sour taste and tea aroma. The selected treatment was the one with the highest antioxidant activity and hedonic value, namely the addition of 3.0% lime and 0.15% MEEg.
Bahasa Indonesia Abstract:
Teh hitam mempunyai aktivitas antioksidan lebih rendah daripada the hijau, warna seduhannya agak gelap dan kurang stabil selama penyimpanan. Oleh karena itu perlu ditambahkan antioksidan alami agar antioksidan meningkat dan warna lebih terang dan stabil. Penelitian ini bertujuan mengetahui pengaruh penambahan perasan jeruk nipis dan minyak esensial Eucalyptus globulus (MEEg) terhadap akivitas antioksidan dan warna, serta organoleptik hedonic seduhan teh hitam. Metode penelitian yang digunakan metode eksperimen yang terdiri dari 2 tahap, yaitu tahap penentuan lama penyeduhan teh hitam dan tahap penambahan perasan jeruk nipis (0, 1, 2, 3% v/v) dan MEEg (0,00, 0,05, 0,10, dan 0,15% v/v). Hasil penelitian menunjukkan bahwa lama waktu penyeduhan terbaik adalah 8 menit dengan nilai IC<sub>50</sub> 1411,24±75,79 ppm, nilai pH 5,25±0,02, warna kuning merah (<sup>o</sup>Hue 75,93± 3,16), dan nilai lightness 47,09±1,06. Penambahan perasan jeruk nipis cenderung menurunkan aktivitas antioksidan, total fenolik, total flavonoid, dan total tanin terkondensasi, tetapi penambahan MEEg meningkatkan aktivitas antioksidan, total fenolik, total flavonoid, dan total tanin terkondensasi seduhan teh hitam. Penambahan perasan jeruk nipis dan MEEg meningkatkan kesukaan terhadap warna seduhan teh dan rasa mint, tetapi menurunkan kesukaan terhadap rasa asam dan aroma teh. Perlakuan terpilih adalah yang memiliki aktivitas antioksidan dan nilai hedonik tertinggi yaitu penambahan jeruk nipis 3,0% dan MEEg 0,15%.</p
We did a comparative analysis of tea and raw tea materials. There is an increase in the content of carotenoids and flavonoids (thearubigins and theaflavins) in June, a decline in July, and August, and consequently a slight increase again in other months. The increase is due to unfavorable conditions – drought during these periods. In raw new variety forms No. 855 and No. 582, as well as in black tea variety form No. 582 (0.09 mg.g-1), we determined the high value of theaflavins (0.10; 0.11 and 0.09 mg.g-1, respectively). The highest content of thearubigins was found in variety forms No. 582 and No. 3823 (1.33 mg.g-1 and 1.17 mg.g-1). Ascorbic acid is significantly disintegrated (on average 96 – 97%) in the production of black tea. In green tea, ascorbic acid disintegrates to a lesser extent, leaving about 13% of its initial amount in the raw material. The dynamics of GPOD activity in a 3-leaf sprout are variety-specific. At the beginning of the growing season (May), the activity of the enzyme was low – in the range of 0.363 to 0.607 g-unit in sec. In June, there is a decrease in activity, which, however, is not significant (p <0.05) and is due to the biological characteristics of the tea culture. In green tea, the ruthine is on average 3 times more than in black tea (on average about 38.09 and 12.12 mg.100g-1, respectively). We have identified 11 amino acids; the highest percentage accounted for proline (from 30 to 70%), valine (17 – 30%), and serine (about 10%). We have identified 11 amino acids in Krasnodar tea, a large proportion of these amino acids has proline, valine, and serine. There was a variation in the content of biologically active substances depending on genotype characteristics. Studies have identified some controversial issues that require explanation and further study.
Tea (Camellia sinensis) being the most consumed beverage worldwide. The safety evaluation of tea needs to be monitored during pregnancy, prenatal as well as postnatal developmental period beside its beneficial roles toward health and disease. Black Tea extract (BTE) may have an impact on thyroid hormone physiology and reproductive health during pregnancy. The objective of present study was to evaluate the role of BTE on thyroid physiology of pregnant rat during prenatal and postnatal period. Among three experimental groups, Group 1 was the control pregnant female rats respectively treated orally with saline, Group 2 and Group 3 were pregnant female rats treated with 50 mg and 100 mg BTE/kg body weight/day, p.o. respectively throughout prenatal and postnatal periods. All three groups of rats were provided balance diet and drinking water ad libitum. Animals were examined through their T3, T4, TSH, E2 and P4 hormone assay and histology of thyroid, ovary and uterus. All data were expressed as mean ± standard deviation with significance between the controls and the treated groups (n = 6). Experimental data were subjected to the ANOVA and Tukey test; P < 0.05 was considered as statistically significant. BTE treatment significantly increased the levels of T3 and T4 whereas decreased TSH level. BTE also alters the shape of thyroid follicles, follicular epithelium and colloid content in the lumen. This study confirmed BTE induced hyperthyroidism during pregnancy.
The efficiency of extracts with antioxidant properties of plum pulp, black tea and green tea leaves was evaluated, analyzing the induction periods (IP) and rate constants (k) at 110 °C, in the 1st, 30th, 57th and 91st day of storage. Antioxidant activity was observed in all extracts, either by the rate constant decrease or by the induction period increase. The higher induction period obtained was 9.15 h for the black tea leaves extract while the lower was 6.97 h for the green tea leaves extract. The control had an average induction period of 6.95 h for the first day. The models obtained are significant and showed determination coefficients greater than 0.90 with no significance lack of fit at the level of 5%. The optimization with maximization of the induction period and minimization of the rate constant showed that the black tea extract was the most suitable to avoid oxidation. On the first day of test, the optimization indicates the mixture containing 50% of black tea and 50% of plum pulp extract as the best mixture. The optimizations provided a variation of 8.92 < IP (h) < 9.69 and 0.25 < k (h⁻¹) < 0.38.
Cancer chemoprevention by natural dietary agents has received considerable importance because of their cost-effectiveness and wide safety margin. However, single agent intervention has failed to bring the expected outcome in clinical trials; therefore, combinations of chemopreventive agents are gaining increasing popularity. The present study aims to evaluate the combinatorial chemopreventive effects of resveratrol and black tea polyphenol (BTP) in suppressing two-stage mouse skin carcinogenesis induced by DMBA and TPA. Resveratrol/BTP alone treatment decreased tumor incidence by ∼67% and ∼75%, while combination of both at low doses synergistically decreased tumor incidence even more significantly by ∼89% (p<0.01). This combination also significantly regressed tumor volume and number (p<0.01). Mechanistic studies revealed that this combinatorial inhibition was associated with decreased expression of phosphorylated mitogen-activated protein kinase family proteins: extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase 1/2, p38 and increased in total p53 and phospho p53 (Ser 15) in skin tissue/tumor. Treatment with combinations of resveratrol and BTP also decreased expression of proliferating cell nuclear antigen in mouse skin tissues/tumors than their solitary treatments as determined by immunohistochemistry. In addition, histological and cell death analysis also confirmed that resveratrol and BTP treatment together inhibits cellular proliferation and markedly induces apoptosis. Taken together, our results for the first time lucidly illustrate that resveratrol and BTP in combination impart better suppressive activity than either of these agents alone and accentuate that development of novel combination therapies/chemoprevention using dietary agents will be more beneficial against cancer. This promising combination should be examined in therapeutic trials of skin and possibly other cancers.
Tea is an important dietary source of flavanols and flavonols. In vitro and animal studies provide strong evidence that tea polyphenols may possess the bioactivity to affect the pathogenesis of several chronic diseases, especially cardiovascular disease and cancer. However, the results from epidemiological and clinical studies of the relationship between tea and health are mixed. International correlations do not support this relationship although several, better controlled case-referent and cohort studies suggest an association with a moderate reduction in the risk of chronic disease. Conflicting results between human studies may arise, in part, from confounding by socioeconomic and lifestyle factors as well as by inadequate methodology to define tea preparation and intake. Clinical trials employing putative intermediary indicators of disease, particularly biomarkers of oxidative stress status, suggest tea polyphenols could play a role in the pathogenesis of cancer and heart disease.
Green tea (Camellia sinensis) is rich in catechins, of which (−)-epigallocatechin-3-gallate (EGCG) is the most abundant. Studies in animal models of carcinogenesis have shown that green tea and EGCG can inhibit tumorigenesis during the initiation, promotion and progression stages. Many potential mechanisms have been proposed including both antioxidant and pro-oxidant effects, but questions remain regarding the relevance of these mechanisms to cancer prevention. In the present review, we will discuss the redox chemistry of the tea catechins and the current literature on the antioxidant and pro-oxidative effects of the green tea polyphenols as they relate to cancer prevention. We report that although the catechins are chemical antioxidants which can quench free radical species and chelate transition metals, there is evidence that some of the effects of these compounds may be related to induction of oxidative stress. Such pro-oxidant effects appear to be responsible for the induction of apoptosis in tumor cells. These pro-oxidant effects may also induce endogenous antioxidant systems in normal tissues that offer protection against carcinogenic insult. This review is meant point out understudied areas and stimulate research on the topic with the hope that insights into the mechanisms of cancer preventive activity of tea polyphenols will result.
Background: The flavonoid components of tea have been associated in epidemiological studies with a decreased risk of cardiovascular disease. Flavonoids have been shown to have antioxidant and vasodilator effects in vitro; we therefore postulated that drinking green or black tea attenuates the well-characterized acute pressor response to caffeine and lowers blood pressure during regular consumption.
Objective: To determine whether green and black tea can attenuate the transient pressor effect of caffeine, or lower blood pressure during regular consumption.
Methods: In the first study, the acute effects of four hot drinks - green tea and black tea (at a dose equivalent to four standard cups), water matched to the teas for caffeine content ('caffeine') and water - were assessed in 20 normotensive men using a Latin-Square designed study. Clinic blood pressure was measured before and 30 and 60 min after each drink had been ingested. In the second study, the effects on blood pressure of regular green and black tea ingestion were examined in 13 subjects with high-normal systolic blood pressure and mild systolic hypertension (systolic blood pressure in the range 130-150 mmHg) using a three-period crossover study. Five cups per day of green tea, black tea and caffeine (in hot water and matched to the teas) were consumed for 7 days each, in random order. Twenty-four hour ambulatory blood pressure was measured at the end of each seven-day intervention. Results are presented as means and 95% confidence intervals (CI).
Results: An acute pressor response to caffeine was observed. Relative to caffeine, there were further acute increases in systolic and diastolic blood pressure at 30 min among those drinking green tea [5.5 mmHg (95%CI -21.4 to 12.4) and 3.1 mmHg (95%CI -0.1 to 6.3), respectively] and black tea [10.7 mmHg (95%CI 4.0 to 17.4) and 5.1 mmHg (95%CI 1.8 to 8.4), respectively]. The changes in blood pressure at 60 min were not significant. The effect on 24-h ambulatory systolic and diastolic blood pressure of regular drinking of green tea [increases of 1.7 mmHg (95%CI -1.6 to 5.0) and 0.9 mmHg (95%CI -1.3 to 3.1), respectively] or black tea [increase of 0.7 mmHg (95%CI -2.6 to 4.0) and decrease of 0.7 mmHg (95%CI -2.9 to 1.5), respectively] was not significant relative to caffeine.
Conclusions: Contrary to our initial hypothesis, tea ingestion caused larger acute increases in blood pressure than caffeine alone. However, any acute effects of tea on blood pressure did not translate into significant alterations in ambulatory blood pressure during regular tea consumption.
The Oxygen Radical Absorbance Capacity (ORAC) assay was used to determine the total antioxidant capacity of tea. Green and black teas (n = 18) had a mean antioxidant capacity of 761.1 ± 85.3 μmol Trolox Equivalents (TE) per g dry matter. However, their antioxidant capacity varied from 235 μmol to over 1526 μmol Trolox equivalents (TE)/g dry matter, and total phenolics ranged from 32 to 147 mg/g in different commercial teas. One tea phenolics extract had an antioxidant capacity of 4796 μmol TE/g dry matter and 625 mg total phenolics/g. On a dry matter basis, an antioxidant capacity of 761 μmol TE/g is considerably higher than any of the other fruits and vegetables measured in our laboratory. However, since dry tea is not consumed directly, brewing conditions may influence the final antioxidant capacity in the tea as consumed. We tested both green and black teas by placing one tea bag (1.95 g) in 150 ml (5 oz.) of boiling water. In the first brewed cup, approximately 84% of the total antioxidant activity was solubilized within the first 5 min of brewing. An additional 13% of the antioxidant activity was extracted into the second glass of 150 ml with an additional 5 min of brewing. At the dilutions obtained after the first brewing, the tea as consumed would contain approximately 8.31 μmol TE per ml. This total antioxidant capacity compares to other drinks from fruits and vegetables that had antioxidant capacity values ranging from 1.6 to 15 μmol TE/ml. At these antioxidant levels, consumption of 150 ml of tea could make a significant contribution to the total daily antioxidant capacity intake. (−)-Epicatechin and (+)-catechin, two components from tea, had an antioxidant capacity of 2.36 and 2.49 μmol/μmol or 8.13 and 8.58 μmol/mg, respectively. In 16 tea samples we observed a mean of 10.0 ± 0.6 μmol TE/mg total phenolics. Tea can be an important source of what has been referred to as “non-nutrient” antioxidant phytochemicals. However, with the variation that exists in antioxidant capacity with various tea preparations, measures of antioxidant capacity intake are critical to the study of intake and health outcomes and/or biomarkers of health outcomes.
Tea is one of the most widely consumed beverages worldwide. Several studies have suggested that catechins and theaflavins found in tea may reduce the risk of various types of cancers. Major advances have been made to understand the molecular events leading to cancer prevention; however, the evidence is not conclusive. Evidence from pre-clinical and clinical studies also suggests that persistent inflammation can progress to cancer. Several possible mechanisms of action may explain the cancer preventive aspects of tea components specifically anti-inflammatory effects. In regards to brain health, green tea catechins have been recognized as multifunctional compounds for neuroprotection with beneficial effects on vascular function and mental performance. Theanine, a unique amino acid in tea, enhances cognition in humans and has neuroprotective effects. Human interventional studies with well characterized tea products are needed.
Tea is the most popular beverage, consumed by over two thirds of the world's population. Tea is processed differently in different parts of the world to give green (20%), black (78%) or oolong tea (2%). Green tea is consumed mostly in Japan and China. The antimutagenic and anticarcinogenic activities of green tea are extensively examined. The chemical components of green and black tea are polyphenols, which include EC, ECG, EGC, EGCG and TFs. This article reviews the epidemiological and experimental studies on the antimutagenicity and anticarcinogenicity of tea extracts and tea polyphenols. In Japan, an epidemiological study showed an inverse relationship between habitual green tea drinking and the standardized mortality rates for cancer. Some cohort studies on Chanoyu (Japanese tea ceremony) women teachers also showed that their mortality ratio including deaths caused by malignant neoplasms were surprisingly low. The antimutagenic activity against various mutagens of tea extracts and polyphenols including ECG and EGCG has been demonstrated in microbial systems (Salmonella typhimurium and Escherichia coli), mammalian cell systems and in vivo animal tests. The anticarcinogenic activity of tea phenols has been shown in experimental animals such as rats and mice, in transplantable tumors, carcinogen-induced tumors in digestive organs, mammary glands, hepatocarcinomas, lung cancers, skin tumors, leukemia, tumor promotion and metastasis. The mechanisms of antimutagenesis and anticarcinogenesis of tea polyphenols suggest that the inhibition of tumors may be due to both extracellular and intracellular mechanisms including the modulation of metabolism, blocking or suppression, modulation of DNA replication and repair effects, promotion, inhibition of invasion and metastasis, and induction of novel mechanisms.
The effect of black tea on the level of uric acid (UA) and C-reactive proteins (CRP) in humans susceptible to ischemic heart diseases was assessed in a prospective randomized controlled study. The study group consumed 9 g of black tea (equivalent to three cups of tea) daily for 12 weeks without additives followed by a 3-week wash-out (with control group consuming equivalent volume of hot water). Black tea consumption induced a highly significant decrease in the high uric acid baseline groups >6 mg/dL by 8.5%; p < 0.05. For men and women in the base line group >7 mg/dL, the decrease was 9.4% and 7.1%, respectively. In the low baseline serum uric acid levels there was a non-significant increase of 3.7% and 15% in men and women, respectively. C-reactive protein in the high risk group >3 mg/L was significantly decreased by 53.4% and 41.1% in men and women, respectively. For the non-supplemented group in this range the changes were 3.7% decrease for men and 2.9% increase for women. Tea supplementation-associated decrease in plasma uric acid and C-reactive protein levels may benefit humans at high risk of cardiovascular events and may augment drug therapy.