High blood pressure, also known as hypertension, usually exhibits no symptoms until it reaches a severe stage. The American Heart Association warns that uncontrolled hypertension can cause many serious conditions, some of which can lead to death, including stroke, angina, congestive heart failure, heart attack, kidney damage and fluid in the lungs. If your systolic blood pressure goes above 180 mm Hg or your diastolic blood pressure goes above 110 mm Hg, you need immediate medical attention. Caffeine, including from black tea, is a dietary factor that can negatively affect your blood pressure.
Caffeine and Blood Pressure
Caffeine from any source can cause a quick blood pressure increase, although health experts do not know the cause. Mayo Clinic emeritus hypertension specialist Dr. Sheldon G. Sheps explains that this phenomenon can occur even if you do not have hypertension. However, black tea does not seem to have a significant effect on blood pressure over time. Caffeine affects different people's blood pressure differently, and some people build a tolerance. If your blood pressure goes up by five to 10 points within 30 minutes of having caffeine, then caffeine might have an effect on you.
Amount
It takes two to three cups of coffee for the caffeine to affect your blood pressure. Black tea has less caffeine than coffee, so it would take more black tea than coffee to boost your blood pressure from caffeine. An 8 oz. cup of coffee contains anywhere from 95 mg to 200 mg of caffeine, depending on the variety. An 8 oz. serving of black tea contains 40 mg to 120 mg of caffeine. Green, white and herbal teas contains less caffeine, so you might want to try them to reduce your caffeine intake.
Reducing Caffeine
If you have high blood pressure, Sheps recommends cutting caffeine out of your diet, or at least reducing it to 200 mg or less daily. However, reduce it slowly so you can minimize withdrawal symptoms. Avoid caffeine before you engage in other blood-pressure-increasing activities such as exercise.
Considerations
A 1999 study in "Journal of Hypertension" on the flavonoids in black tea found that black tea increased blood pressure separately from the caffeine, although not by significant amounts. However, a January 2004 study in "The Journal of Nutrition" on stroke-prone spontaneously hypertensive rats found that the polyphenols in the black tea reduced hypertension by small amounts. More research is needed to form a conclusion.
References
- American Heart Association; Why Blood Pressure Matters; Jun. 24, 2011
- MayoClinic.com; How Does Caffeine Affect Blood Pressure?; Sheldon G. Sheps; Nov. 14, 2009
- "Journal of Hypertension"; Effects on Blood Pressure of Drinking Green and Black Tea; J.M. Hodgson, et al.; April 1999
- MayoClinic.com; Caffeine Content for Coffee, Tea, Soda and More; Oct. 3, 2009
- "The Journal of Nutrition"; Black and Green Tea Polyphenols Attenuate Blood Pressure Increases in Stroke-Prone Spontaneously Hypertensive Rats; Hiroko Negishi, et al.; Jan. 1, 2004
