Effects on blood pressure of drinking green and black tea

Background The flavonoid components of tea have been associated in epidemio logical studies with a decreased risk of cardiovascular disease. Flavonoids have been shown to have antioxidant and vasodilator effects in vitro; we t herefore postulated that drinking green or black tea attenuates the well-ch aracterized acute presser response to caffeine and lowers blood pressure du ring regular consumption. Objective To determine whether green and black tea can attenuate the transi ent presser effect of caffeine, or lower blood pressure during regular cons umption. Methods In the first study, the acute effects of four hot drinks - green te a and black tea (at a dose equivalent to four standard cups), water matched to the teas for caffeine content ('caffeine') and water - were assessed in 20 normotensive men using a Latin-Square designed study. Clinic blood pres sure was measured before and 30 and 60 min after each drink had been ingest ed. In the second study, the effects on blood pressure of regular green and black tea ingestion were examined in 13 subjects with high-normal systolic blood pressure and mild systolic hypertension (systolic blood pressure in the range 130-150 mmHg) using a three-period crossover study. Five cups per day of green tea, black tea and caffeine (in hat water and matched to the teas) were consumed for 7 days each, in random order. Twenty-four hour ambu latory blood pressure was measured at the end of each seven-day interventio n. Results are presented as means and 95% confidence intervals (CI). Results A n acute presser response to caffeine was observed. Relative to caffeine, th ere were further acute increases in systolic and diastolic blood pressure a t 30 min among those drinking green tea [5.5 mmHg (95%CI -1.4 to 12.4) and 3.1 mmHg (95%CI -0.1 to 6.3), respectively] and black tea [10.7 mmHg (95%CI 4.0 to 17.4) and 5.1 mmHg (95%CI 1.8 to 8.4), respectively]. The changes i n blood pressure at 60 min were not significant The effect on 24-h ambulato ry systolic and diastolic blood pressure of regular drinking of green tea [ increases of 1.7 mmHg (95%CI -1.6 to 5.0) and 0.9 mmHg (95%CI -1.3 to 3.1), respectively] or black tea [increase of 0.7 mmHg (95%CI -2.6 to 4.0) and d ecrease of 0.7 mmHg (95%CI -2.9 to 1.5), respectively] was not significant relative to caffeine. Conclusions Contrary to our initial hypothesis, tea ingestion caused larger acute increases in blood pressure than caffeine alone, However, any acute effects of tea on blood pressure did not translate into significant alterat ions in ambulatory blood pressure during regular tea consumption. J Hyperte ns 1999, 17:457-463 (C) Lippincott Williams & Wilkins.