Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together by Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW
RATIONALE: Although both contain behaviourally significant
concentrations of caffeine, tea is commonly perceived to be a less
stimulating drink than coffee. At least part of the explanation for
this may be that theanine, which is present in tea but not coffee,
has relaxing effects. There is also some evidence that theanine
affects cognitive performance, and it has been found to reduce
blood pressure in hypertensive rats.
OBJECTIVES: To study the subjective, behavioural and blood
pressure effects of theanine and caffeine administered alone and
together, in doses relevant to the daily tea consumption of regular
tea drinkers.
MATERIALS AND METHODS: In a randomised, double-blind,
placebo-controlled study, healthy adult participants (n = 48)
received either 250-mg caffeine, 200-mg theanine, both or neither
of these. They completed ratings of mood, including anxiety, and
alertness, and had their blood pressure measured before and
starting 40 min after drug administration. Anxiety was also
assessed using a visual probe task.
RESULTS: Caffeine increased self-rated alertness and jitteriness
and blood pressure. Theanine antagonised the effect of caffeine on
blood pressure but did not significantly affect jitteriness,
alertness or other aspects of mood. Theanine also slowed overall
reaction time on the visual probe task.
CONCLUSIONS: Theanine is a physiologically and behaviourally
active compound and, while it is unclear how its effects might
explain perceived differences between tea and coffee, evidence
suggests that it may be useful for reducing raised blood
pressure.
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