What is Tea??

Camellia sinensis

Tea ConsumptionWorldwide – (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

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

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

Beverage Polyphenols(mg/240 mL)

Consumption(mL/day)

Polyphenols(mg/day)

Tea (Black) 600 77 193

Beer 45 233 44

Wine (Red) 434 13.4 24

Coffee 21 226 20

Grape Juice (Red) 361 6.4 10

Orange Juice 54 19.3 4

Apple Juice 41 17.5 3

Pineapple Juice 64 9.7 3

U.S. Per Capita BeveragePolyphenol Consumption

Slide courtesy of: Joe Vinson, PHD, vinson@UofS.edu

Quantity of Polyphenolsin the Top 10 Beverages

Beverage Mg Polyphenols/240 ml

Green Tea

Black Tea

965

840

Red Wine 434

Prune Juice 394

Red Grape Juice 362

Pineapple Juice 250

White Grape Juice 202

Cranberry Juice 137

Grapefruit Juice 110

Orange Juice 53Slide courtesy of: Joe Vinson, PHD, vinson@UofS.edu

Quantity of Polyphenolsin dry leaf depends on:

How leaves are processed

Geography, Growing conditions

 

Quantity of Polyphenols in brewed tea depends on

  Brew time, Amount used, Decaffeination, Temperature

• Brewed, hot tea is the highest

• Lower in instant and ready to drink teas

• Adding milk does not interfere

 

New Database this fall for Flavonoids in about 250 foods:

  www.nal.usda.gov/fnic/foodcomp

Relative Contributions of PolyphenolsFrom all Sources in U.S. Diet

Tea22%

Other Beverages

12%

Fruits28%

Vegetables26%

Nuts12%

Spices/Oils0%

Slide courtesy of: Joe Vinson, PHD, vinson@UofS.edu

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??

Cardiovascular Effects of TeaCHD:

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??

 

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

CancerAnimal 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

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

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

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

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.

A presentation to the Northern Colorado Dietetics Association, presented by Lori Bricker, MSRD. (970) 221-5520 lori@theteatable.com

October 16, 2002