Probably all of us know that life events and ‘stress’ can change our mood, but there’s less acknowledgement, I think, that what we can have impact here too. One example relates to blood sugar imbalance: if blood sugar levels plummet it can switch on the body’s stress response, which in turn can induce feelings of tension and/or anxiety. Of course, it’s always possible that foodstuffs may have the opposite effect, and help regain or retain a state of calm.
One foodstuff that, anecdotally, is reputed to do this is tea. Interestingly, a recent study published in the American Journal of Clinical Nutrition  found that Japanese adults drinking at least 5 cups of green tea a day were at a 20 per reduced risk of ‘psychological distress’, compared to those consuming 1 cup a day or less. Epidemiological studies of this nature do not prove that green tea has an anti-stress effect, just that green-tea drinking is associated with improved mental well-being.
However, there is at least some evidence which suggests that tea can have genuine mood-enhancing effects.
In a study published in 2007, the effects of tea on the stress response was tested in a group of men . The study subjects were all taken off caffeinated beverages, and put on to a caffeinated ‘placebo’ drink for a period of 4 weeks. After this, the men were put through a challenging task, measures of the stress response were made before, during and after the task. After this, men were given either tea or placebo-drink to consume for a period of 6 weeks, at which point their responses to stress were re-checked.
Some measures, including heart rate and blood pressure, were not different between the two groups. However, some were.
Compared to those drinking the placebo drink, tea-drinkers had reduced ‘platelet activation’ (platelet activation makes the blood more likely to clot and is activated during the stress reponse).
Tea drinkers also had lower cortisol levels after the challenging task (cortisol is a major hormone secreted in response to stress).
And finally, tea-drinkers also felt more relaxed after completing the challenging task.
These findings suggest that tea-drinking may have at least some capacity to mitigate against the negative effects of stress.
1. Hozawa A, et al. Green tea consumption is associated with lower psychological distress in a general population: the Ohsaki Cohort 2006 Study. Am J Clin Nutr 2009;90(5):1390-6
2. Steptoe A, et al. The effects of tea on psychophysiological stress responsivity and post-stress recovery: a randomised double-blind trial. Psychopharmacology (Berl) 2007;190(1):81-9