Green tea extract is made from the unfermented leaves of the Camellia sinesis plant. Proponents of green tea state it contains the largest amount of antioxidants of any tea. Antioxidants protect cell DNA from damage by scavenging and destroying potentially harmful molecules called free radicals. Doses of 100 to 750 mg of green tea extract, sold in capsules, are taken as antioxidants. Ask your doctor before taking green tea extract because side effects can occur.
Catechins
The more fermentation the tea leaves undergo, the fewer polyphenols they contain. Polyphenols have antioxidant properties. Because green tea leaves undergo no fermentation but are steamed, they contain high amounts of polyphenols called catechins. Catechins, which make up 30 percent of the dry weight of the tea leaves, according to the Pennington Nutrition Series, are more effective antioxidants than vitamins C or E, Harvard Health Productions states. The most active catechin in green tea, epigallocatechin gallate, or EGCG, is also the best studied. Green tea extract capsules contain the catechins from the tea.
Stimulants
Green tea extracts, such as green tea, also contains caffeine, although black tea contains two to three times the caffeine of green tea. Caffeine can increase mental alertness and a sense of well-being but can also cause irritability, a rapid heartbeat, dizziness, headache, decreased appetite, nausea, diarrhea, stomach upset, insomnia or jitteriness in large quantities. Other stimulants found in green tea extract include theobromine and theophylline.
Benefits
Green tea and green tea extracts lower cholesterol and triglyceride levels, according to the University of Maryland Medical Center. Green tea may also reduce heart disease by lowering blood pressure and decreasing the risk of atherosclerosis. In countries such as Japan where people consume large amounts of green tea, cancer occurs less frequently. Green tea may also help you lose weight and may help regulate blood glucose levels. However, the U.S. Food and Drug Administration does not allow manufacturers of green tea extract or green tea to claim that the product reduces the risk of heart disease, saying that evidence is not conclusive.
Risks
Concentrated green tea extracts have caused liver problems in some people, reports the National Center for Complementary and Alternative Medicine. Taking green tea extract with food may help reduce the risk of liver disease. Report any signs of liver disease such as jaundice, abdominal pain or dark-colored urine to your doctor promptly. Because green tea contains small amount of vitamin K, it can decrease the effectiveness of blood thinners such as warfarin. Green tea extract can also interact with adenosine, a medication that prevents irregular heartbeat.
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