"This has important health implications, because slow recovery following acute stress has been associated with a greater risk of chronic illnesses such as coronary heart disease," said lead researcher professor Andrew Steptoe from University College London.
The researchers recruited 75 healthy young males with an average age of 33 and put them through a four-week "washout" period during which they were not allowed to consume tea, coffee, caffeinated beverages, aspirin, ibuprofen, dietary supplements, and fruits and vegetables rich in flavonoids. Then, 37 of the men were given four cups of black tea per day for six weeks while the 38 members of the placebo group were given an identical-tasting caffeinated drink, with no active tea ingredients, for the same time period.
Both groups were asked to perform stressful tasks, including verbally responding to threats of unemployment and accusations of shoplifting while sitting in front of a camera. The researchers measured the cortisol, blood pressure and blood platelet levels, and also asked the subjects to self-rate their stress levels.
According to the results -- published in the online issue of the journal Psychopharmacology and scheduled for printing in the next physical issue -- both groups showed significant increases in blood pressure, heart rate and subjective stress levels during the tasks. However, 50 minutes after the tasks were complete, cortisol levels in the tea-drinking group had dropped by 47 percent compared to only 27 percent in the placebo group.
Additionally, the tea drinkers showed lower blood platelet activation -- which has been linked to blood clotting and subsequent heart attack risk -- and a greater degree of relaxation after the tasks.
"Tea, therefore, appears to influence the effectiveness of post-stress recovery, rather than the magnitude of stress responses themselves," wrote the researchers.
The researchers noted that previous animal and human studies have reported tea flavonoids affected sympathetic nervous systems in rats; human brain wave activity was stimulated by the amino acid theanine, found in tea; and EGCG reportedly has a sedative effect and reduces responses to separation stress.
"Although it does not appear to reduce the actual levels of stress we experience, tea does seem to have a greater effect in bringing stress hormone levels back to normal," the researchers said of the of the study, which was funded by the U.K.'s BBSRC, Unilever Research and the British Heart Foundation.
"This just goes to show what I've been saying for years," says health advocate and "The Seven Laws of Nutrition" author Mike Adams. "You don't need prescription drugs to deal with everyday stress. Natural beverages such as black tea can help you deal with tension without any dangerous side effects, and when you combine these natural foods and beverages with regular exercise, stress barely affects you at all."