Objectives: Flavonoids may protect against cardiovascular disease. Tea is a major source of dietary flavonoids. Studies indicate black tea improves endothelial function but data on arterial haemodynamics, blood pressure (BP) and insulin resistance are equivocal. Inconsistency may be due to flaws in study design or flavonoid doses tested. Further, no study has evaluated the dose–response curve. Our study aimed to test the effects of various doses of black tea on vascular function, BP and insulin resistance.
Methods: According to a randomized, double-blind, controlled, cross-over design, 19 healthy men were assigned to receive either five treatments with a twice daily intake of black tea (0, 100, 200, 400 and 800 mg tea flvanoids/day) in five periods lasting 1 week each.
Results: Black tea dose dependently increased flow-mediated dilation (FMD) from 7.8% (control) to 9.0, 9.1, 9.6 and 10.3% after the different flavonoid doses, respectively (P = 0.0001). Already 100 mg/day (less than 1 cup of tea) increased FMD compared with control (P = 0.0113). FMD improvement after 800 mg/day was significant compared with control (P < 0.0001) but also to 100 mg/day (P = 0.0121) and 200 mg/day (P = 0.0275). Black tea intake decreased office systolic (−2.6 mmHg, P = 0.0007) and diastolic (−2.2 mmHg, P = 0.006) BP as well as stiffness index (P = 0.0159) without changes in other parameters studied.
Conclusion: Our study is the first showing black tea ingestion dose dependently improved FMD and decreased peripheral arterial stiffness in healthy volunteers. Our data suggest that worldwide all tea drinkers could benefit from protective cardiovascular effects exerted by tea.
aDepartment of Internal Medicine and Public Health, University of L'Aquila, Italy
bDepartment of Internal Medicine and Public Health, Viale S. Salvatore, Delta 6 Medicina, 67100 - Coppito - L'Aquila, Italy
cUnilever Food and Health Research Institute, Olivier van Noortlaan 120, P.O. Box 114, 3130 AC Vlaardingen, The Netherlands
Received 26 June, 2008
Revised 20 November, 2008
Accepted 11 December, 2008
Correspondence to Davide Grassi, MD, University of L'Aquila, Department of Internal Medicine and Public Health, Viale S. Salvatore, Delta 6 Medicina, 67100 Coppito L'Aquila, Italy Tel: +39 0862 434744; fax: +39 0862 434749; e-mail: email@example.com