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Green Tea

Next to water, green tea is the second most consumed beverage in the world. It has been used for centuries in India and China for its medicinal purposes and is now used across the world for this reason. Green tea contains antioxidants called polyphenols and regular consumption of the beverage can protect against the formation of heart disease, some forms of cancer, accelerated aging, and even the common cold.

 

Claimed Health Benefits

  • Powerful antioxidant

  • Lowers cholesterol and triglyceride levels

  • Decreases blood clotting

  • Boosts immune system

  • Helps protect against some forms of cancer

  • Helps with weight loss

 

Food Sources

Green tea beverage

 

Dose

Dosages that have shown to have the greatest health benefit range anywhere from 125-500mg/day, with a 60% concentration of polyphenols. This would be comparable to 4-10 cups of green tea per day.

 

Evidence for Health Benefits

  • Although human studies are limited, the studies that have been conducted have shown promising results. For example, there have been studies done on cancer patients receiving chemotherapy and radiation treatments. The patients drinking green tea had more white blood cells than those not drinking green tea. This means that those consuming green tea had a boosted immune system.

  • In an animal study involving female mice, researchers wanted to look at the weight-loss effects of green tea. Half of the mice were supplemented with green tea for 4 months, and the other half were not. The results of the study showed that the mice receiving green tea consumed less food, lost weight and body fat, and decreased their blood cholesterol and triglyceride levels. An interesting finding was that the mice consuming the green tea experienced a decrease in blood leptin levels. This is important because leptin is a hormone that is thought to act as an appetite suppressant. However, most obese people have large amounts of leptin circulating in their bodies, suggesting they might be insensitive to the hormone. This leads researchers to believe that green tea may be a regulator of body weight.

  • A study involving 10 healthy men looked at the affect of green tea on energy expenditure (metabolism) in a 24-hour period. The men were split into 3 groups. The first group received green tea (containing 50mg caffeine and 90mg of polyphenols); the second group received 50mg of pure caffeine; the last group received a placebo. Each of the 3 groups had to take their assigned treatment at breakfast, lunch, and supper for one day. The results showed that those who received the green tea had a 4% increase in their metabolic rate of about 80 calories compared with the men given the placebo. The men receiving the green tea also had an increase in the use of body fat as an energy source, whereas the men supplemented with the 50mg of pure caffeine (the same amount found in the green tea) did not. This suggests that the increase in metabolism when consuming green tea is not due solely to the caffeine content. There are other constituents of green tea that help increase metabolism.

 

Cautions

Consumption of up to 20 cups of green tea per day has shown no adverse side effects except for restlessness and increased heart rate (the same as caffeine).

Individuals taking blood-thinning medications should speak to their physician before consuming large amounts of green tea as it could increase bleeding time.

Tea contains polyphenols, which are antioxidant compounds that inhibit iron absorption from plant foods. Therefore, frequent consumption of tea could promote iron deficiency.

 

References

1. Healthnotes, Inc. (2003) Helping People Lead Healthier Lives. http://www.healthwell.com/healthnotes/healthnotes.cfm?ContentID=2102007 Accessed June 16, 2003.

2. SupplementWatch, Inc. (2002) Supplement Decisions Made Easy. http://www.supplementwatch.com/supatoz/supplement.asp?format=printable&supplementId=159 Accessed June 16, 2003.