Antioxidant Effects of Tea: Evidence from Human Clinical Trials

Abstract

Tea remains the most consumed drink in the world after water, well ahead of coffee, beer, wine and carbonated soft drinks. An accumulated number of population studies suggests that consumption of green and black tea beverages may bring positive health effects (1). One hypothesis explaining such effects is that the high levels of flavonoids in tea can protect cells and tissues from oxidative damage by scavenging oxygen-free radicals. Chemically, the flavonoids found in green and black tea are very effective radical scavengers. The tea flavonoids may therefore be active as antioxidants in the digestive tract or in other tissues after uptake. A substantial number of human intervention studies with green and black tea demonstrates a significant increase in plasma antioxidant capacity in humans approximately 1 h after consumption of moderate amounts of tea (1-6 cups/d). There are initial indications that the enhanced blood antioxidant potential leads to reduced oxidative damage to macromolecules such as DNA and lipids. However, the measurement of oxidative damage through biomarkers needs to be further established. In conclusion, tea flavonoids are potent antioxidants that are absorbed from the gut after consumption. Tea consumption consistently leads to a significant increase in the antioxidant capacity of the blood. Beneficial effects of increased antioxidant capacity in the body may be the reduction of oxidative damage to important biomolecules. The scientific support is strongest for the protection of DNA from oxidative damage after black or green tea consumption. However, the quality of the studies now available is insufficient to draw firm conclusions. Therefore, further evidence from human intervention studies is required.

Effect of green tea powder on thermal, rheological & functional properties of wheat flour and physical, nutraceutical & sensory analysis of cookies

“…Table 4 shows that the percent inhibition of DPPH increases with the increase in amount of GTP in wheat flour. This is largely because, tea and tea products mainly contain polyphenols and compounds like myristic acid and palmitic acid, which are natural antioxidants and have been demonstrated to show antioxidative, anti-carcinogenic and anti-microbial properties (Ahmad et al 2013;Rietveld and Wiseman 2003).…”

Health benefits of Green and Black Tea: A Review

“…Black tea, obtained by tea leaves with fermentation, is oxidized and contains mainly multimeric polyphenols, whose biological activity is not well documented [5]. And Oolong teais a partially oxidized product [6].Green tea is best studied for decades for its health benefits, including cancer chemo preventive and chemotherapeutic effects [7], [8] butin recent years, black tea is also extensively investigated mainly regarding its influence on human health [9].…”

Black tea – helpful or harmful? A review of the evidence

“…Tea makes a significant contribution to dietary intakes of flavonoids; one UK study estimated a figure of 82% (Hertog et al, 1997). This impacts significantly on plasma antioxidant capacity when up to six cups per day are consumed (Rietveld and Wiseman, 2003), although interpretation of the eight studies reporting this was hampered by differences in assay methods and how results were expressed.…”

“…Green tea leaves contain more catechins, while black tea leaves, which undergo oxidation during manufacturing, contain more complex thearubigins and theaflavins. As yet, these have been more difficult to identify than the single catechins but they also exhibit antioxidant activity (Rietveld and Wiseman, 2003). Flavonoids in tea are absorbed from the upper intestine, more rapidly in the case of the catechins present in green tea (Rietveld and Wiseman, 2003), although plasma antioxidant potential is similar after consuming green vs black tea (Leenen et al, 2000).…”

“…As yet, these have been more difficult to identify than the single catechins but they also exhibit antioxidant activity (Rietveld and Wiseman, 2003). Flavonoids in tea are absorbed from the upper intestine, more rapidly in the case of the catechins present in green tea (Rietveld and Wiseman, 2003), although plasma antioxidant potential is similar after consuming green vs black tea (Leenen et al, 2000). The uptake of theaflavins found in black tea is relatively low compared with catechins, but this may be masked by imprecise methodologies that do not detect all of the theaflavin metabolites (Mulder et al, 2001).…”