The effect of an herbal supplement containing black tea and caffeine on metabolic parameters in humans.

Objective: The objective of this study was to test an herbal supplement containing black tea (the fully oxidized form of Camellia sinensis) and caffeine for stimulation of thermogenesis.

Methods/materials: A double-blind, placebo-controlled, crossover study was conducted on 16 healthy, weight-stable, non-smoking subjects, ages 21-55 years, with body mass index (BMI) of 20-30 kg/m2, and on no medications other than oral contraceptives or hormone replacement therapy. Subjects had no caffeine for 48 hours, no exercise for 24 hours, and no food for 12 hours before each visit. Area under the curve (AUC) for resting metabolic rate (RMR), respiratory quotient (RQ), blood pressure, pulse rate, and temperature were measured. At each visit RMR was measured at baseline and at one and two hours following oral administration of a supplement containing principally 600 mg black tea extract (60 percent polyphenols, 20 percent caffeine) and 442 mg guarana extract (36 percent caffeine) or matching placebo.

Results: The RMR and systolic blood pressure (SBP) AUCs increased significantly (p less than 0.02 and p less than 0.01, respectively) in the herbal supplement group compared to placebo. The AUC increase in RMR over the two-hour test period was 77.19 kcal/24 hr2 +/- 120.10 kcal/24 hr2 with an average rise of 52.38 +/- 29.52 kcal/24 hrs. The AUC rise in SBP over two hours was 10.3 mm Hg/hr +/- 14 mm Hg/hr. The average rise in SBP over two hours was 3.7 mm Hg +/- 4.4 mm Hg.

Discussion: The herbal supplement increased metabolic rate without changing substrate oxidation. The rise in SBP was consistent with the amount of caffeine the supplement contained.