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Health Benefits of Tea

From cardiovascular health to weight management, it's wise to drink up

Next to water, tea is the most widely consumed drink in the world.1 Tea drinking is a habit that should be encouraged, because it can provide health benefits.

Flavonoids

The health benefits of tea are primarily attributed to its flavonoid content. Flavonoids are polyphenolic compounds that occur in tea, cocoa, fruits, vegetables and wine. Flavonoids contribute significantly to taste and color, and possibly help maintain certain normal, healthy body functions.2

Black, green, white and oolong teas are rich natural sources of flavonoids providing between 100 mg and 300 mg of total flavonoids per 240-mL serving. Approximately 65.4% of flavonoids consumed by U.S. adults are from tea.3,4 The amount of flavonoids in a tea brew depends on many factors, including the type of tea used (loose leaf, standard tea bag or pyramid tea bag) and how many times the tea bag is squeezed.2 The majority of flavonoids are infused from the tea leaves to the brew after 4 minutes of brewing (without stirring or squeezing).5

The type and quantity of flavonoids found in different types of teas depends on the level of processing the tea leaves undergo. A major step in tea production is the halting of the oxidation process at a predetermined stage, depending on the type of tea sought. For example, Lipton Green Tea and Lipton Black Tea both contain about the same amount of total flavonoids and caffeine content. However, the number of catechins in Lipton Green Tea is much higher than that in Lipton Black Tea.6 This type of detail is available on package labeling.                                                                                                                    

Catechins

Catechins are the main flavonoids produced by the Camellia sinensis plant, which produces green, black, oolong and white teas. During the oxidation process, enzymatic activity allows for the catechins to be polymerized, which alters their structure. Green tea, typically heated soon after harvesting, undergoes minimal oxidation. This preserves the majority of the catechins. Substantial oxidation under controlled temperatures and humidity helps produce black tea. Enzymatic reaction changes the color of the leaves from green to brown and produces the polymerization of catechins into theaflavins and thearubigins. To produce oolong tea, oxidation is stopped somewhere in between that required for green and black tea. Theaflavins are the main catechins in green tea and oolong tea. Thearubigins are the catechins in black tea.

The chemical structures of the catechins have yet to be fully identified, but the flavonoids in tea have been studied in vitro and in vivo. In vitro studies measuring the antioxidant capacity of tea using oxygen radical absorbance capacity and trolox equivalent antioxidant capacity assays demonstrate the antioxidant capacity of a cup of black or green tea to be more than twice as effective as servings of common fruit juices.7,8

Experimental (in vitro) evidence supports the concept that tea is a source of powerful flavonoids. However, the physiologic relevance of this fact needs further study in the context of human metabolism. So far, human studies designed to substantiate the beneficial effects suggested by in vitro experiments and animal studies have not produced evidence that flavonoids have sufficient antioxidant capacity to influence human metabolism.

Flavonoid Metabolism

The bulk of human studies focusing on the antioxidant properties of tea show an increase in plasma antioxidant capacity after the consumption of black or green tea.9-12 That tea consumption increases the antioxidant capacity of plasma is well known, but whether this effect is directly related to the action of tea flavonoids alone is unknown. Other elements may also help bring about the antioxidant response in the human body.14

Dietary flavonoids, including tea catechins, are absorbed by the small intestine. Flavonoids can be poorly absorbed once total catechin content is absorbed. In addition, chemical forms of flavonoids in foods may be different from in vivo versions. Catechins in green tea are an exception because they can reach systemic circulation without further modification. Catechins in black tea reach the colon after not being absorbed by the small intestine and can then be degraded.15,16 Research shows that drinking tea reliably increases the antioxidant volume of plasma. Current investigations are studying whether tea flavonoids are singularly responsible for increased antioxidants in plasma or other tea components contribute to this effect.

More Benefits

Advising patients to consume two to three cups of tea per day as a simple healthy lifestyle strategy is a recommendation with scientific support. Tea does not act as a diuretic, nor is it dehydrating.1,15,17

In addition to the benefits already outlined, tea ingestion can be linked to a reduced risk for cardiovascular disease. Two studies found that drinking three or more cups of tea daily is associated with an 11% reduced incidence of myocardial infarction and a 21% reduced risk of ischemic stroke.18,19 Possible mechanisms for this effect are improved blood vessel and vascular function. Vascular function can be measured noninvasively using flow-mediated dilation (FMD) of the brachial artery. Several large studies have determined that tea may improve FMD results, likely due to flavonoid content.20-22

Patients seeking to lower low-density lipoprotein (LDL) cholesterol may find drinking tea advantageous. Two controlled studies documented reductions in total and LDL cholesterol. The patients in the study drank five cups of tea a day (about 722 mg of flavonoids) and experienced cholesterol reductions.13 In another study, patients who took daily doses of tea extract capsules containing 300 mg of tea flavonoids experienced lowered total and LDL cholesterol.23

Tea has several other significant health benefits, including enhanced cognition, weight management, immunity and oral health. A study by De Bruin found that drinking two or three cups of black tea with 45 mg of theanine and 100 mg of caffeine over 1 to 2 hours helps improve alertness and maintain focus. The combination of theanine and caffeine is likely responsible for these effects.24

As a plain beverage (without milk, sugar or other additives with calories), tea contains a negligible amount of calories. When helping patients manage a healthy weight, tea is an ideal choice. Catechin-enriched green tea may have a positive effect on body composition and weight management.25 These effects have been repetitively shown in Asian populations; the research needs replication in Western populations.

In addition, green tea intake may help with fat oxidation and increased energy expenditure. In one study, a high green tea consumption containing 375 mg/day of catechins and 150 mg/day of caffeine helped increase energy expenditure and fat oxidation in animals and humans.26 Other studies indicate that longer-term consumption of green tea and its components may have benefits for fat mass distribution and body weight, but well-designed long-term studies have not shown these effects.27,28

Robyn Kievit is a family nurse practitioner, a registered dietitian and a certified specialist in sports dietetics. She operates a private nutrition practice in Boston and is on staff at Emerson College. E-mail your nutrition and weight loss questions to robyn@robynkievit.com or visit her website at www.robynkievit.com. On Facebook and Twitter, search for nutritionmentor.

References

1. Popkin BM, et al. A new proposed guidance system for beverage consumption in the United States. Am J Clin Nutr. 2006;83(3):529-542.

2. Astill C, et al. Factors affecting the caffeine and polyphenol contents of black and green tea infusions. J Agric Food Chem. 2001;49(11):5340-5347.

3. Chun OK, et al. Estimated dietary flavonoid intake and major food sources of U.S. adults. J Nutr. 2007;137(5):1244-1252.

4. Chun OK, et al. Estimated intake of proanthocyanidin in the US population. Abstract presented at Experimental Biology, New Orleans, April 20, 2009.

5. Peterson J, et al. Tea variety and brewing techniques influence flavonoid content of black tea. J Food Comp Analysis. 2004;17(3-4):397-405.

6. Lipton Institute of Tea website. http://www.lipton.com/en_en/Lipton_Institute_of_Tea-1,10.aspx. Accessed Sept. 20, 2011.

7. Cao GH, et al. Antioxidant capacity of tea and common vegetables. J Agric Food Chem. 1996;44(11):3426-3431.

8. Wang H, et al. Total antioxidant capacity of fruits. J Agric Food Chem. 1996;44(3):701-705.

9. Serafini M, et al. In vivo antioxidant effect of green and black tea in man. Eur J Clin Nutr. 1996;50(1):28-32.

10. Maxwell SR. Antioxidant vitamin supplements: update of their potential benefits and possible risks. Drug Safe. 1999;21(4):253-266.

11. Serafini M, et al. Inhibition of human LDL lipid peroxidation by phenol-rich beverages and their impact on plasma total antioxidant capacity in humans. J Nutr Biochem. 2000;11(11-12):585-590.

12. Sung H, et al. In vivo antioxidant effect of green tea. Eur J Clin Nutr. 2000;54(7):527-529.

13. Langley-Evans SC. Consumption of black tea elicits an increase in plasma antioxidant potential in humans. Int J Food Sci Nutr. 2000;51(5):309-315.

14. Lotito SB, Frei B. Consumption of flavonoid-rich foods and increased plasma antioxidant capacity in humans: cause, consequence or epiphenomenon? Free Radic Biol Med. 2006;41(12):1727-1746

15. Gardner EJ, et al. Black tea-helpful or harmful? A review of the evidence. Eur J Clin Nutr. 2007;61(1):3-18.

16. Panel on Dietary Reference Intakes for Electrolytes and Water, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, D.C.: National Academies Press; 2005.

17. Maughan RJ, Griffin J. Caffeine ingestion and fluid balance: a review. J Hum Nutr Diet. 2003;16(6):411-420.

18. Peters U, et al. Does tea affect cardiovascular disease? A meta-analysis. Am J Epid. 2001;154(6):495-503.

19. Arab L, et al. Green and black tea consumption and risk of stroke: a meta-analysis. Stroke. 2009;40(5):1786-1792.

20. Hooper L, et al. Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2008;88(1):36-50.

21. Duffy SJ, et al. Short- and long-term black tea consumption reverses endothelial dysfunction in patients with coronary artery disease. Circulation. 2001;104(2);151-156.

22. Grassi D, et al. Black tea consumption dose-dependently improves flow-mediated dilation in healthy males. J Hypertens. 2009;27(4):774-781.

23. Maron DJ, et al. Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized, controlled trial. Arch Intern Med. 2003;163(12):1448-1453.

24. De Bruin EA. Drinking black tea improves attention and alertness. Presented at Tea and the Brain, New York, NY, Sept. 16, 2008.

25. Boon N. Health potential for functional green teas? Int J Vitam Nutr Res. 2008;78(6):275-281.

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

27. Dulloo AG, et al. Normal caffeine consumption - influence on thermogenesis and daily energy-expenditure in lean and postobese human volunteers. Am J Clin Nutr. 1989;49(1):44-50.

28. Chantre P, Lairon D. Recent findings of green tea extract AR25 (Exolise) and its activity for the treatment of obesity. Phytomedicine. 2002;9(1):3-8.


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