New clinical trial from Britain put tea’s relaxing reputation to the test, with rewarding results 10/16/2006
There’s considerable evidence that drinking tea regularly can reduce the risk of Alzheimer's and certain cancers and discourage weight gain. The evidence for green tea tends to be a bit stronger, but black tea matches it or runs a close second in several prevention categories, including breast cancer.
And, as the authors of a recently published study said, “Tea has anecdotally been associated with stress relief.…” But until now, tea’s relaxing reputation had never been put to a reliable scientific test.
The positive results of a recent British experiment could hold important implications for increasing quality of life and for reducing the risks of heart disease and Alzheimer’s, which seem to be increased by chronic stress.
A team at University College London set out to test the folk tradition in a rigorous, placebo-controlled trial.
They recruited 75 healthy young men (average age 33), who avoided tea, coffee, caffeinated drinks, aspirin, ibuprofen, dietary supplements, and fruits and vegetables rich in flavonoids for a four-week “wash-out” period before the study began.
The men were then split randomly into two groups. Every day for six weeks, one group drank four cups of a fruit-flavored beverage containing the same amounts of caffeine and presumed active constituents found in black tea, including its characteristic polyphenol antioxidants and tannins.
At the same time, the control group consumed four cups a day of a caffeinated placebo drink that was identical in taste and color but lacked black tea’s characteristic polyphenol antioxidants and tannins.
The men in both groups were given challenging tasks, and the researchers measured their cortisol, blood pressure, blood platelet and self-rated levels of stress. For example, the participants were placed in front of a video camera and told to respond to a stressful situation such as a threat of being fired or being accused of shop lifting.
Those tasks raised the men’s blood pressure, heart rates and subjective stress ratings, with no difference in blood pressure or heart rate between the groups.
The researchers detected no reduction in levels of stress hormones among the tea group during the challenges, compared with the placebo group.
But, as lead author Andrew Steptoe said in a UCL press release, “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 UCL team found that within an hour of the stress challenges, levels of the key stress hormone called cortisol dropped by an average of 47 percent in the tea-drinking group, versus only 27 percent in the faux-tea group.
Chronically elevated cortisol levels appear to damage brain cells in the hippocampus: a part of the brain needed to transfer information from our senses into memory. Depression actually causes the hippocampus to shrink in size, while Alzheimer's disease affects the hippocampus first and severely, before other parts of the brain.
In fact, tea’s ability to reduce cortisol levels more quickly following stressful experiences could be partly responsible for its link to reduced rates of Alzheimer’s among heavy tea drinkers.)
The tea group also showed less inflammation-induced “activation” of blood platelets, which increases the stickiness of blood and the risk of heart attacks.
Finally, the black tea group reported feeling more relaxed after the stress challenges, compared with the placebo group.
Lead author Professor Andrew Steptoe noted that his team could not identify which of the compounds in tea, were responsible for the relaxing response seen in the trial: “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.”
But it appears likely the polyphenol antioxidants in tea are key players in its stress-recovery-accelerating effects.
The results of prior studies show that tea’s antioxidant polyphenols—especially EGCG—calm the sympathetic nervous system of rats. In addition, tea is a rare source of an amino acid called theanine that crosses the blood-brain barrier and exerts several beneficial effects:
- Promotes production of alpha waves in the brain, which are commonly associated with a state of alert relaxation.
- Modulates levels of serotonin and dopamine.
- Reduces damaging “excitotoxicity” from sources of excess glutamate such as MSG.
- Increases production of a relaxing, anti-anxiety “inhibitory neurotransmitter” called gamma-aminobutyric acid (GABA). It is believed that the GABA-release-promoting properties of theanine blunt the brain effects of the caffeine obtained from drinking tea, versus the caffeine obtained from drinking coffee.
So it seems that to keep our brains working well longer, we should all get in the habit of quaffing a “cuppa” (as the Brits would say) as often as we can.
- Steptoe A, Gibson EL, Vounonvirta R, Williams ED, Hamer M, Rycroft JA, Erusalimsky JD, Wardle J. The effects of tea on psychophysiological stress responsivity and post-stress recovery: a randomised double-blind trial. Accessed online October 12, 2006 at http://www.springerlink.com/content/m226111566k24u65/.
- University College London. Black tea soothes away stress. Accessed online October 12, 2006 at http://www.ucl.ac.uk/media/library/tea.