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The Nutritional Impact of Tea


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This is a lecture I gave a few years ago to the Northern Colorado Dietetic Association in Fort Collins, CO.

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The Nutritional Impact of Tea

  1. 1. <ul><li>What is Tea?? </li></ul>Camellia sinensis
  2. 2. Tea Consumption Worldwide – (per capita consumption = 120 mL/day) 76-78% Black tea 20-22% Green tea <2% Oolong In USA--50 billion servings per year 90% Black tea 10% Green tea 80%Iced tea Rising Consumption 1990--$1.8 billion 2001--$4.9 billion Research Scientific research began 3 only decades ago 1985--50 publications with ‘tea’ in title 2002-- increased to 275
  3. 3. Green Tea vs. Black Tea Black Tea Primarily consumed in Europe, the UK, the US, and Australia Oxidized or ‘fermented’ Takes 12-18 hours Oxygen reacts with enzymes on leaf surface  Green Tea Primarily consumed in Asia Unoxidized or ‘unfermented
  4. 4. Tea is rich in Polyphenols, especially Flavonoids Over 5000 identified Flavonoids Purpose is to protect plant About 20 basic flavonoids in the diet Antioxidant activity Polyphenols in tea:   Green tea Epicatechin (EC), Epicatechin 3 gallate (ECG) Epigallocatechin (EGC), Epigallocatechin 3 gallate (EGCG)   Black tea– ‘tannins’ Theaflavin, Thearubigens A typical cup = 150-200 mg flavonoids
  5. 5. U.S. Per Capita Beverage Polyphenol Consumption Slide courtesy of: Joe Vinson, PHD, 20 226 21 Coffee 10 6.4 361 Grape Juice (Red) 4 19.3 54 Orange Juice 24 13.4 434 Wine (Red) 3 17.5 41 Apple Juice 3 9.7 64 Pineapple Juice 44 233 45 Beer 193 77 600 Tea (Black) Polyphenols (mg/day) Consumption (mL/day) Polyphenols (mg/240 mL) Beverage
  6. 6. Quantity of Polyphenols in the Top 10 Beverages Slide courtesy of: Joe Vinson, PHD, 202 White Grape Juice 137 Cranberry Juice 110 Grapefruit Juice 53 Orange Juice 250 Pineapple Juice 362 Red Grape Juice 394 Prune Juice 434 Red Wine 965 840 Green Tea Black Tea Mg Polyphenols/240 ml Beverage
  7. 7. Quantity of Polyphenols in dry leaf depends on: <ul><li>How leaves are processed </li></ul><ul><li>Geography, Growing conditions </li></ul><ul><li>  </li></ul><ul><li>Quantity of Polyphenols in brewed tea depends on </li></ul><ul><li>  Brew time, Amount used, Decaffeination, Temperature </li></ul><ul><li>Brewed, hot tea is the highest </li></ul><ul><li>Lower in instant and ready to drink teas </li></ul><ul><li>Adding milk does not interfere </li></ul><ul><li>  </li></ul><ul><li>New Database this fall for Flavonoids in about 250 foods: </li></ul><ul><li> </li></ul>
  8. 8. Relative Contributions of Polyphenols From all Sources in U.S. Diet Slide courtesy of: Joe Vinson, PHD,
  9. 9. Antioxidant Capacity of Tea Flavonoids: In vitro  Scavenge reactive oxygen and nitrogen species Chelate metal ions   In vivo   Human studies are somewhat inconsistent Modest transient increase in plasma antioxidant activity 30-60 min. after ingestion Repeated tea consumption (6 cups/day x 7 days) decreases oxidative status   Animal studies get better results but . . . Higher doses Human genetic variability??
  10. 10. Cardiovascular Effects of Tea CHD: Inverse correlation between flavonoid intake and CVD in Europe, US, Japan Green tea for Japan Black tea otherwise Wales and Scotland: tea intake associated with lower social class Either no correlation or a positive correlation with CHD   Incidence of MI decreases 11% with a tea intake of 3 cups/day   Atherosclerosis:   Green and black tea intake inversely associated with development and progression Black tea may raise total plasma homocysteine levels Caffeine’s effect??  
  11. 11. Cardiovascular Effects of Tea cont. Hypertension:   Recent studies do not show a hypotensive effect for green or black tea Apparently no long term effect   Endothelial Cell Function:   Tea may reverse endothelial vasomotor dysfunction Acute and chronic tea intake improves blood vessel dilation   LDL Oxidation In vitro : Tea extracts significantly inhibit LDL oxidation Ex vivo : Little or no inhibition Concerns: In vitro tea concentrations very high Tea catechins may accumulate in the body Individual variations in tea polyphenol bioavailability
  12. 12. Cancer Animal models: Consistent results Black and Green Tea inhibit tumorigenesis for cancers of: skin, lung, oral cavity, esophagus, stomach, intestine, colon, liver, pancreas, and prostate EGCG inhibits cell proliferation and transformation promotes apoptosis inhibits angiogenesis Not strong evidence that decrease in cancer risk is due to antioxidant activity Caffeine causes apoptosis of damaged cells but not normal ones Need to separate tea’s effects from caffeine’s effects
  13. 13. Cancer cont. Epidemiological studies not as convincing Considerable international variation in tea consumption Small differences in overall cancer rates Differences in tea type and preparation, temperature, lifestyle How to measure tea consumption?? Dry leaf weight, brewed volume, per day, per week??   Need human intervention trials
  14. 14. Other health benefits of Tea: Reduced dental cares Improved bone mineral density Increased thermogenesis (Green tea) Decreased kidney stone formation Negative aspects of tea ingestion:   Interferes with non-heme iron absorption Note: This effect mitigated by addition of lemon or consuming tea between meals
  15. 15. What to tell our patients? Tea is a nutritionally sound, low-calorie, addition to a healthy diet Add milk or lemon if desired, no bad effects May help lower the risk for cardiovascular disease and some cancers Promotes oral health and has other physiological benefits Both black and green tea are good choices, and ideally, both should be consumed
  16. 16. What to tell our patients? cont. Caffeine content: No good way to tell precisely how much caffeine is in a given tea In general, 1/3 of the amount in coffee, by brewed volume Can reduce the amount of caffeine by about 80%: Begin brewing tea as usual After 30 seconds, discard brewed tea Pour fresh hot water on the same tea leaves and continue brewing Decaffeinated teas are available Flavor is not as good Some evidence that polyphenol’s effects are less Don’t like tea? Try new kinds, try loose tea, try flavored teas--almost everyone can find one they like.
  17. 17. A presentation to the Northern Colorado Dietetics Association, presented by Lori Bricker, MSRD. (970) 221-5520 [email_address] October 16, 2002