From the archives: Regular tea drinking improves creative problem-solving skills, promotes relaxation and reduces stress. In this story, from May 2021, Jennifer Bowden explains how.
Question:
My friend drinks a cup of tea every night, as she says it helps her sleep. I thought tea contained caffeine, so how can a caffeinated drink help you sleep?
Answer:
The humble cup of tea is credited in some intriguing clinical trials with reducing stress and producing a calming feeling. All of which may not surprise tea drinkers, who have long reported feeling relaxed after their regular cuppa. But it is only in the past decade or so that scientists have begun to learn more about this conundrum: a caffeinated drink that relaxes people.
Like coffee, tea contains caffeine, but although a long black has about 200mg of caffeine, a cup of tea contains only about 50mg, the same amount found in a cup of instant coffee. Caffeine increases activity in the brain and nervous system. It also increases the circulation of chemicals in the body, such as the stress hormone cortisol and adrenaline.
However, one double-blinded, randomised clinical trial investigated the impact of caffeine-containing black tea on stress. Seventy-five healthy men had tea and coffee removed from their diet for four weeks and instead drank four cups a day of a caffeinated placebo drink. So, they were still consuming caffeine, just not sourced from tea.
The men were then assigned to receive either a placebo or a tea treatment for six weeks. Researchers disguised the placebo and the tea treatment in the form of fruit-flavoured powders (eg, apple or lemon) to blind participants to what they were receiving. The dose was equivalent to drinking four cups of strong tea a day.
At the end of the six weeks, the participants completed various psychophysiological tests designed to check their stress response. Researchers used a participant’s subjective measures of stress and objective measures, such as checking heart rate, blood pressure and cortisol levels in their saliva.
The research team found the tasks induced substantial increases in blood pressure, heart rate and subjective stress ratings, and there was no difference in response between those who took the tea treatment and those who had the placebo. However, the tea group had lower cortisol levels after the tasks and a relative increase in their subjective measures of relaxation during the recovery period.
In other words, the regular consumption of tea led to lower post-stress cortisol and greater relaxation. It seems black tea may have health benefits resulting from its ability to aid in stress recovery.
Studies have also found that drinking tea improves creative problem-solving. This may be the result of tea’s ability to reduce stress and induce a more positive mood, as creative thinking is linked to positive moods.
It certainly seems that tea contains some rather magical ingredients. For starters, the flavonoids in tea are well-known antioxidants, but they may also influence our central nervous system. Studies have shown that tea flavonoids inhibit the action of the sympathetic nervous system in rats; the sympathetic nervous system prepares the body for fight or flight.
Another component found almost exclusively in tea is an amino acid called L-theanine, which may contribute to recovery from stress. Oxford University researchers used an electroencephalograph to monitor brain activity in individuals who ingested an L-theanine solution, and they found greater activity in the alpha frequency band. This type of brainwave occurs when we are awake and … wait for it … relaxed. The researchers concluded that L-theanine, at realistic dietary levels, may induce a relaxed but alert mental state through its influence on our central nervous system.
L-theanine may also reduce the effects of caffeine on our cognitive function and arousal, explaining why consumption of caffeine-containing tea results in a relaxed but alert state. Or maybe tea is relaxing only in people who aren’t affected by caffeine, given we all have variable responses. Of course, we must also consider whether the acts of making a cup of tea, then sitting down to drink it, contribute to our relaxed mood. But given the results of these clinical trials, I’m inclined to think there is more to the humble cup of tea than meets the eye.
This story was originally published in the May 29–June 4, 2021 issue of the Listener.
