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LONDON -- Drinking black tea reduces measures of stress-related hormones and harmful cardiovascular changes, reported researchers here. In short, it seems to calm jangled nerves.
LONDON, Oct. 5 -- Drinking black tea reduces measures of stress-related hormones and harmful cardiovascular changes, reported researchers here. In short, it seems to calm jangled nerves.
In a double-blind placebo-controlled study, tea drinkers had lower levels of cortisol following a stress challenge, felt more relaxed, and had reduced platelet activation than placebo drinkers, reported Andrew Steptoe, D.Sc.., of University College London, and colleagues, in the online edition of Psychopharmacology.
"Drinking tea has traditionally been associated with stress relief, and many people believe that drinking tea helps them relax after facing the stresses of everyday life," said Dr. Steptoe. "However, scientific evidence for the relaxing properties of tea is quite limited."
To determine what effect drinking black tea might have on stress, the authors conducted a parallel group, double-blind randomized trial. Their goal was to subjectively assess the effects of tea consumption of cardiovascular, cortisol, and platelet responses to acute stress.
They recruited 75 healthy non-smoking men who agreed to be withdrawn from tea, coffee, and other caffeinated beverages during a four-week washout period. During that time, the participants were given a fruit-flavored caffeinated placebo tea. The volunteers also refrained from using NSAIDs or taking dietary or caffeine supplements, and restricted their diet to avoid fruits rich in antioxidant flavonoids that could have skewed or masked the association of tea with stress reduction.
At the end of the washout period, the volunteers were subjected to a psychophysiological evaluation, and were then randomized to either six weeks of a fruit flavored-black tea preparation or a fake-tea placebo.
The tea preparation was based on the components of an average cup of black tea, and included theobromine, epicatechin, catechin, epigallocatechin, flavonoids, and other compounds. The sachets provided contained 6.4% flavonols, and were equivalent to four cups of strong black tea per day.
In all, 38 patients were assigned to placebo, and 38 to active tea. Patients were evaluated at baseline, during the study, and afterward with cardiovascular measures, and both cortisol and platelet activation were assessed before and after stress-inducing tasks. The tasks were designed to produce increases blood pressure, heart rate, and subjective stress ratings.
The authors found no significant between-group differences in response to stress at baseline. But when they looked again after six weeks, they found that the tea drinkers had lower levels of platelet activation, assessed by flow cytometry, both before and after being subjected to stress than did placebo drinkers (P