Second only to water, tea is the most popular beverage in the world. For many people, it serves as the primary source of polyphenols, powerful antioxidants that neutralize free radicals. Green tea reduces your risk of cardiovascular disease and possibly calms your mood. Yet green tea is also believed to enhance concentration and energy, thanks at least in part to the 15 to 40 mg of caffeine contained in the typical cup of green tea. The impact of tea on blood pressure reflects these paradoxical effects caused by different active ingredients in tea.
Caffeine and Blood Pressure
The amount of caffeine you get when you consume a cup of tea depends on several factors, including how long you've steeped the tea and whether the tea has been decaffeinated. Although the caffeine in two or three cups of coffee -- about 200 to 600 mg -- can trigger a short-term yet significant increase in blood pressure, tea contains far less caffeine than coffee and so may cause less of an increase in blood pressure.
Tea and Short-Term Effects on Blood Pressure
A review article published in the October 16, 2008, issue of "Archives of Internal Medicine" examined five randomized controlled studies of the effect of tea consumption on blood pressure. The five studies reviewed involved 343 subjects who participated in the studies for a period of at least seven days, with a median duration of four weeks. Tea had no effect in the short term on blood pressure. However, a study of the more immediate effects of tea on blood pressure did find effects. A study published in the April 1999 issue of "Journal of Hypertension" conducted by researcher Jonathan Hodgson found modest increases in diastolic and systolic blood pressure at 30 minutes but not at 60 minutes following ingestion of green tea.
Green Tea and Endothelial Function
The endothelium, a layer of cells that line the inner surface of your blood vessels, reduces the turbulence of blood flow, allowing blood to be pumped more efficiently. Epigallocatechin gallate, or EGCG, is a potent polyphenol contained in green tea. Among its positive long-term effects, EGCG improves functioning of the endothelium, according to a review article by Jonathan Hodgson in the September 2006 edition of "Clinical and Experimental Pharmacology & Physiology." The May 2007 issue of "American Journal of Physiology -- Endocrinology and Metabolism" indicates that EGCG can help in the dilation of blood vessels and capillaries, an effect that would reduce blood pressure.
Long-Term Effects on Blood Pressure
Animal and epidemiological studies indicate that long-term consumption of green tea lowers blood pressure, reports Hodgson in his 2006 review study. For example, Hodgson found in a study published in the "Journal of Nutrition" in September 2003 that higher intake of tea was associated with lower blood pressure in a sample of women who were more than 70 years-old. Short-term intervention studies, however, yield mixed results, generally showing no effect on blood pressure. On the other hand, an epidemiological study in a Chinese population published in the July 2004 issue of "Archives of Internal Medicine" found that habitual moderate consumption of green or oolong tea for more than one year reduced the risk of developing chronic high blood pressure.
Interactions
Green tea might interact with monoamine oxidase inhibitors, often called MAO-inhibitors, to cause a severe increase in blood pressure, according to the University of Maryland Medical Center. Also, caffeine in green tea can interact with phenylpropanolamine, a compound contained in many cough and cold medications, to cause mania and a dramatic increase in blood pressure.
References
- "Archives of Internal Medicine"; Effect of Cocoa and Tea Intake on Blood Pressure; Dirk Taubert, et al.; October 2008
- "Archives of Internal Medicine"; The Protective Effect of Habitual Tea Consumption on Hypertension; Yi-Chang Yang, et al.; July 2004
- "American Journal of Physiology -- Endocrinology and Metabolism"; EGCG, a Green Tea Polyphenol, Improves Endothelial Function and Insulin Sensitivity, Reduces Blood Pressure, and Protects Against Myocardial I/R Injury in SHR; Maria Potenza, et al.; May 2007
- "Clinical and Experimental Pharmacology & Physiology"; Effects of Tea and Tea Flavonoids on Endothelial Function and Blood Pressure: A Brief Review; Jonathan Hodgson; September 2006
- University of Maryland Medical Center; Green Tea; September 2010
- "Journal of Nutrition"; Tea Intake is Inversely Related to Blood Pressure in Older Women; Jonathan Hodgson, et al; September 2003
