Issue 102, September 2008
Black Tea Reduces Stress Levels
The old adage that there is nothing that can't be helped by a good cup of tea appears to be true. Researchers at the University College London have found that tea consumption helps us to recover more quickly from stresses of everyday life by lowering stress hormone levels in the body.
The study found that people who drank tea were able to reduce their stress more quickly than those who drank a placebo. Furthermore, the study participants who drank black tea four times a day for six weeks were found to have lower levels of the stress hormone cortisol in their blood after a stressful event, compared with a control group who drank a placebo for the same period of time.
In the study 75 young male tea drinkers were split into two groups. Each group gave up their normal tea drinking habits; one was given a fruit flavoured caffeinated tea made up of the average constituents of black tea and the other a caffeinated placebo. Both groups were subjected to challenging tasks, while their cortisol, blood pressure, blood platelet and self-rated levels of stress were measured. The tasks triggered substantial increases in blood pressure, heart rate and subjective stress ratings in both of the groups. However, 50 minutes after the task, cortisol levels had dropped by an average of 47 % in the tea drinking group compared with 27% in the placebo group.
The researchers also found that blood platelet activation, which is linked to blood clotting and the risk of heart attacks, was lower in the tea drinkers and that this group reported a greater degree of relaxation in the recovery period after the task.
The researchers do not yet know which ingredients of tea are responsible for these effects on stress recovery and relaxation. Tea is chemically very complex, with many different ingredients, such as catechins, polyphenols, flavonoids and amino acids that have been found to have effects on neurotransmitters in the brain.
A Dutch research project has found that black tea consumption improved cognitive performance. The participants in the study consumed a variety of common drinks including tea, coffee and others and were then given an IQ test; the tea consumers' performance was significantly better.
And finally: a team of researchers from King's College London investigated the health benefits of tea consumption, and found that it contains powerful antioxidants (polyphenols), which prevent cellular damage, The researchers concluded that drinking three to four cups of tea per day reduces the risk of heart attack, protects against cancer, strengthens bones and protects against tooth plaque and decay.
"Drinking tea is actually better for you than drinking water," says Dr. Carrie Ruxton, a public health nutritionist at King's College London and the study's lead author. "Water is essentially replacing fluid. Tea replaces fluids and contains antioxidants, so it's got two things going for it."
Though many consumers believe that tea - which often contains caffeine - is dehydrating, Dr Ruxton says such an idea is an urban myth. "Studies on caffeine have found very high doses dehydrate and everyone assumes that caffeine-containing beverages dehydrate," she says. "But even if you had a really, really strong cup of tea or coffee, which is quite hard to make, you would still have a net gain of fluid."
The researchers found that average tea consumption was less than three cups per day in the UK and that many younger people were replacing tea with sugary soft drinks. The study's findings were backed by the British Nutrition Foundation and the Tea Council, which funded the research.
Acknowledgement: 'Headlines' Volume 75, Autumn 2007,
National Newsletter of the Neurological Foundation of New Zealand