Green Tea: Drink to Your Health!

Coffee may be the beverage of choice for most Americans, but many people are beginning to brew some green tea daily too. A growing number of studies in the past few years have turned up signs that drinking green tea has a number of health benefits. It may slow the development of certain cancers (1,2), lower the risk of osteoporosis (3), and help prevent cardiovascular disease.

Green tea may also be very important for those at risk of having a heart attack. In a recent study, researchers asked 1900 heart attack survivors about their tea consumption before they had heart problems, then followed them for up to four years. The heaviest tea drinkers – those who drank two or more cups a day – had a 44% lower death rate following their heart attack compared to non-drinkers. Even those that were moderate consumers drinking fewer than fourteen cups weekly, had a 28% lower chance of dying from heart attack (4).

The protective compounds in green tea are potent antioxidant flavonoids called catechins. Researchers believe catechins protect the heart by relaxing the blood vessels so blood can flow more easily. The ability of vessels to widen when needed is a marker of vascular health. A reduction in that function, even temporarily, can contribute to heart disease and the risk of heart attack.

One situation that can temporarily impair vessels' dilation is having high levels of fat in the blood stream. To test out the ability of green tea to protect vessel function, researchers gave participants in one study a fast food meal containing 50 grams of fat. Along with that meal, volunteers also got one of three different beverages: black tea, green tea, or a placebo drink that resembled tea.

The investigators then made ultrasound measurements of an artery in the arm before and after the meal and tea. They found that tea greatly reduced the impact of the high-fat meal on vessel function (5). Green tea was somewhat more effective than black, which has a lower catechin content. This same team of researchers had previously shown the vitamins C and E, both antioxidants, also help improve artery dilation when taken with a high-fat meal.

The study in heart attack survivors should be reassuring to those who've had an attack and have been worried about caffeine in tea. In fact, some researchers in Japan have isolated an amino acid in green tea called l-theanine, which they believe can buffer some of the effects of caffeine (6,7).

Studies such as these will surely spur more research into the potential benefits of green tea on cardiac health. In the meantime, antioxidants like those in green tea and vitamins C and E, can be used in conjunction with a healthful diet and regular exercise to promote good cardiovascular function.

References

1. Hsu SD et al. Chemo-prevention of oral cancer by green tea. Gen Dent 50:140-6, 2002
2. Weisburger JH. Tea and health: the underlying mechanisms. Proc Soc Exp Biol 220:271-5, 1999.
3. Wu CH et al. Epidemiological evidence of increased bone mineral density in habitual tea drinkers. Arch Intern Med, 162:1001-6, 2002.
4. Mukamal K et al. Tea consumption and mortality after acute myocardial infarct. Circulation 105 :2474-79, 2002.
5. Corretti MC et al. Affect of tea consumption on endothelial-dependent flow-mediated vasodilation after high-fat meal. Presented at Am Coll of Cardiologists Meeting, Atlanta, March, 2002
6. Kaduka T et al. Inhibiting effects of theanine on caffeine stimulation evaluated by EEG in the rat. Biosci Biotechnol Biochem.64:287-293, 2000.
7. Juneja LR et al. L-theanine - a unique amino acid of green tea and its relaxation effect in humans. Trends in Food Sci & Tech 10:199-204, 1999.