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~ May 2006 No.204 ~
Many people are trying to get away from their daily coffee fix, and are turning
to tea, in particular green tea, as a healthy alternative. For over 4,000 years
the Chinese have been consuming green tea, in part, because of its perceived
health benefits. The list of diseases that are believed to be prevented or
improved include cancer, rheumatoid arthritis, and cardiovascular disease.
Drinking green tea is said to lower blood cholesterol levels and fight
infections.
green tea by maschissimo
But if you are switching to green tea to avoid the caffeine, it might not be as
simple as you think. Coffee is one of the most popular drinks in the world, but
is also notorious as a source of caffeine. Indeed, many people drink coffee
just to get a jolt and to delay fatigue. Caffeine stimulates the central
nervous system, the cardiac muscle, and the respiratory system. Because of this
stimulatory effect, caffeine loading is now banned for many competitive
athletes. Caffeine is also a diuretic (a drug that increases the rate of urine
excretion). Signs of over consumption of caffeine include irritability,
sleeplessness, irregular heartbeat, dizziness, vomiting, diarrhoea, headache,
or loss of appetite. Women are cautioned to reduce their caffeine intake during
pregnancy.
Green tea, unless it is decaffeinated, also contains caffeine. Normal green tea
itself may contain more caffeine than coffee, but the length of infusion with
hot water, and the number of time you use the green tea leaves can greatly
reduce your caffeine intake. Experiments have shown that tea after a first 5
minute brew contains 32 mg caffeine. But if the same leaves are then used for a
second and then a third five minute brew, the caffeine drops to 12 mg and then
4 mg.
In all cases, it should be remembered to never brew or drink green tea with
boiling water. In some countries, water heating pots have temperature controls
to heat water for green tea preparation. The high temperature can destroy
valuable therapeutic compounds found in green tea,
Table 1: Caffeine Content of Some Common Drinks (per 100 ml)
Coffee brewed from grounds 40 mg1
Expresso coffee 212 mg1
Instant coffee 26 mg1
Coffee liqueur(63 proof) 26 mg1
Lipton black Tea (bag) 33 mg2
Green tea (loose leaves) 32 mg2
1. Reference
2. 1. Monique B. Hicks, Y-H. Peggy Hsieh and Leonard N. Bell. 1996. Tea
preparation and its influence on methylxanthine concentration . Food Research
International 29: 325-330.
3. 2. USDA Agricultural Research Service