Evidence suggests that tea is able to cause a calming effect in the minutes after it is drunk. However, tea contains caffeine, and caffeine has been shown to be an anxiogenic agent in mammals. This apparently paradoxical situation is explainable because tea contains other compounds that may have mood elevating effects. For example, tea also contains L-theanine and catechin flavonoids, both of which have been shown to reduce anxiety. The L-theanine in tea may also be able to antagonise the physiological effects of caffeine. For example, administration of 200 mg L-theanine has been shown to antagonise the blood pressure raising effects of caffeine. Further, some evidence suggests that the effects of caffeine on mood are not simple. Some evidence for example, suggests that under certain circumstances, caffeine can reduce anxiety in some individuals. Experimentally induced anxiety following alcohol consumption has been shown to be be antagonised by caffeine administration in mice.
Administration of caffeine to healthy subjects at 150 mg and 300 mg of caffeine per 45.4 kg body weight significantly increased depression, anxiety and hostility compared to a placebo. The researchers also noted that the timing of the measurements in the post consumption phase of the experiment were pivotal, as the mental effects of caffeine have a narrow window of effect and it would be easy to miss the mood altering effects by mistiming the observations. Some evidence also suggests that coffee consumption may be more problematic for males, with one study showing that male but not female subject experienced significant anxiety from coffee consumption.
However, coffee consumption is associated with mental stress. For example, in one study researchers administered caffeinated or decaffeinated coffee, tea, diet cola, cola, as well as tap water or sparkling water to healthy subjects. The results showed that caffeine consumption causes significant improvements in alertness, reactions times and memory, but also increased the anxiety experienced by the subjects. In another study, 60 mg of caffeine from a cup of coffee has a significant influence on mood and performance. The 60 mg of caffeine from coffee significantly improved a number of aspects of performance including reaction times and mental processing, but also increase tension in the subjects. Coffee may therefore have more of a detrimental effect on anxiety compared to tea, and this perhaps relates to the lack of L-theanine in coffee. Most studies have been performed on healthy subjects, and the effects of caffeine may be more pronounced on those with pre-existing mood disorders.
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