London, Oct 5 (IANS) Drinking at least four cups of black tea a day could help you fight the stresses of everyday life, evidence shows.

Tea has traditionally been associated with stress relief, and many people believe that the beverage helps them relax after facing the stresses of everyday life. However, scientific evidence for the relaxing properties of tea is quite limited.

In the new study, researchers at London's University College studied 75 young male regular tea drinkers splitting them into two groups and monitored them for six weeks, states a release posted in the university website.

While one group was given a fruit-flavoured caffeinated tea mixture made up of the constituents of an average cup of black tea, the other was given a caffeinated placebo identical in taste but devoid of the active tea ingredients.

Both groups were subjected to challenging tasks, while their cortisol, blood pressure, blood platelet and self-rated levels of stress were measured.

In one task, volunteers were exposed to one of three stressful situations (threat of unemployment, a shop lifting accusation or an incident in a nursing home), where they had to prepare a verbal response and argue their case in front of a camera.

The tasks triggered substantial increases in blood pressure, heart rate and subjective stress ratings in both of the groups. In other words, similar stress levels were induced in both groups. However, 50 minutes after the task, cortisol levels had dropped by an average of 47 percent in the tea drinking group compared with 27 percent in the fake tea group.

Researchers also found that blood platelet activation - linked to blood clotting and the risk of heart attacks - was lower in tea drinkers, and that this group reported a greater degree of relaxation in the recovery period after the task.

This is one of the first studies to assess tea in a double-blind placebo controlled design - that is, neither we nor the participants knew whether they were drinking real or fake tea, UCL Professor Andrew Steptoe said.

"We do not know what ingredients of tea were responsible for these effects on stress recovery and relaxation. Tea is chemically very complex, with many different ingredients.

"Ingredients such as catechins, polyphenols, flavonoids and amino acids have been found to have effects on neurotransmitters in the brain, but we cannot tell from this research which ones produced the differences," the researcher said.

"Nevertheless, our study suggests that drinking black tea may speed up our recovery from the daily stresses in life. 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."

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, Steptoe said.