Black tea consumption dose-dependently improves flow-mediated dilation in healthy males.
OBJECTIVE
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 flavonoids/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.


CONCLUSIONS
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.
Grassi
Davide
D
Department of Internal Medicine and Public Health, University of L'Aquila, L'Aquila, Italy. davide.grassi@cc.univaq.it
Mulder
Theo Pj
TP
Draijer
Richard
R
Desideri
Giovambattista
G
Molhuizen
Henri Of
HO
Ferri
Claudio
C
D000293:Adolescent; D000328:Adult; D000368:Aged; D001158:Arteries / Q000502:physiology; D001794:Blood Pressure; D018660:Blood Pressure Monitoring, Ambulatory; D002097:C-Reactive Protein / Q000032:analysis; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004730:Endothelium, Vascular / Q000502:physiology; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000502:physiology; D013662:Tea; D014664:Vasodilation
D005419:Flavonoids; D013662:Tea; D009569:Nitric Oxide; D002097:C-Reactive Protein