By: Thomas Pickering, MD, DPhil, FRCP, Director of Integrative and Behavioral Cardiology Program
of the Cardiovascular Institute at Mount Sinai School of Medicine, New York.

Tea contains caffeine, which tends to raise blood pressure temporarily, but it also has other substances such as flavonoids, which are thought to protect against heart disease and other disorders. The acute and long-term effects of drinking tea have not been well studied.

In an Australian study, these effects have now been examined. In the first part of the study, 20 men had their blood pressure measured on four separate occasions, during each of which they consumed a different hot drink. These were, black (regular) tea, Japanese green tea, hot water with the same amount of caffeine as the tea, and hot water alone. During the hour after the drink, caffeine raised the blood pressure by about 6mm Hg systolic and 3 mm Hg diastolic. Black tea produced a bigger increase (16/8 mmHg), while green tea produced an intermediate increase (12/6 mmHg).

In the second part of the study 13 men and women with borderline hypertension were studied over 3 weeks, and had their pressures measured over 24 hours with an ambulatory monitor at the end of each week. During each week they drank 5 cups a day of either black tea, green tea, or hot water with caffeine. There was no effect of either type of tea on blood pressure.

Doctor’s comments

Other studies have shown that drinking tea (especially green tea) appears to be good for the heart, and this study shows that, while black tea may raise blood pressure acutely more than would be expected from its caffeine content, over the long term, neither type of tea has much effect on blood pressure. However, since the teas were compared against caffeine, and caffeine does raise pressure slightly, it cannot be concluded with certainty from this study that drinking tea has no effect on blood pressure, but any effect is unlikely to be of significance.

Where it was published