In the short term (about 1-2 hours) the 60-140 mg of caffeine in a 16oz cup of tea can raise blood pressure but some of that effect is countered by theanine, which is calming. A common myth is that the caffeine in tea makes tea dehydrating, which would raise blood pressure by causing blood vessels to constrict, but this is not true. Tea is most definitely hydrating, which further minimizes the short term increase in blood pressure.
Tea (particularly green and hibiscus tea) contains natural ACE inhibitors which:
- Relax blood vessels, increasing blood flow
- Inhibit liver enzymes from triggering water and salt retention, reducing blood volume
“Researchers writing in the latest issue of the European Journal of Cardiovascular Prevention and Rehabilitation have found that people who drink green tea have better blood vessel function just 30 minutes later.” —WebMD
Long term benefits are more pronounced and significant:
- The tannins in tea reduce cholesterol and triglycerides, which lead to heart disease and stroke.
- Antioxidants found in tea and in hibiscus significantly improve the health of the interior surface of blood vessels, protecting them from the hardening and narrowing which leads to hypertension and clogged arteries.
“In a study of 600 habitual green or oolong tea drinkers, those who drank 120 to 599 milliliters per day, decreased their risk of developing hypertension by 46 percent.” —Dr. Yi-Ching
Researchers analyzed 25 randomized controlled trials of the effects of tea on blood pressure and found systolic blood pressure was reduced by an amount which “would be expected to reduce stroke risk by 8%, coronary artery disease mortality by 5% and all-cause mortality by 4% at a population level.” —TIME