Just when the health benefits of green tea seemed entrenched in mainstream thought, a study prompts caution for green-tea drinkers with hypertension. Details, here.
The health benefits of green tea have been widely promoted and include an association with a lower risk of cancer and cardiovascular disease. Previous studies, however, have shown that the catechins in green tea that offer these health benefits may also interfere with the absorption of certain drugs via their effects on drug transporters such as P-glycoprotein and organic anion-transporting polypeptide (OATP); both are found in the intestinal epithelium and participate in uptake of drugs from the gut. A recent European study suggests a catechin-blocking effect on the absorption of the beta-blocker nadolol.
The small study of healthy volunteers published in Clinical Pharmacology and Therapeutics, explored this mechanism in a clinical setting. The authors found that green tea may have a possible negative interaction with the antihypertensive effects of nadolol. In a group of healthy volunteers, individuals who drank at least 2 cups (700 mL) of green tea vs the same amount of water for 2 weeks had decreased efficacy of a single dose of the blood pressure–lowering effects of nadolol. A total of 10 non-smokers who were otherwise healthy participated in a randomized cross-over study separated by a 1-week washout period. Consumption of all juices that may interfere with OATP1A2 (apple, cranberry, graprefruit, orange) was prohibited. Plasma concentrations following a single 30-mg dose of nadolol were 76% lower in participants who drank green tea than in those who drank water. Both HR and BP responses were also lower in green-tea drinkers.
Because this is a very small study, the results are not yet generalizable to the overall population without further validation. Furthermore, the applicability of these findings to other more potent beta-blocking medications is unknown. The study does, however, demonstrate the clinical potential for food-drug interactions that can occur. At this time, clinicians with patients taking nadolol may want to warn their patients about the potential mechanism of interaction with green tea. This interaction may vary depending on the amount of green tea consumed and the dose of nadolol given.
Misaka et al. Green tea ingestion greatly reduces plasma concentrations of nadolol in healthy subjects. Clin Pharmacol Ther. 2014 Jan 13. doi: 10.1038/clpt.2013.241.