Seventy-four healthy individuals participated in a double-blind, randomized placebo-controlled study and were given oral green tea (400 mg powder three times daily) or placebo for 5weeks. The evaluation of reward learning and response to reward was conducted as well as mood, using the Montgomery-Asberg depression rating scale (MADRS) and the Hamilton Rating Scale for Depression (HRSD-17).
Green tea had significantly decreased reaction time in response to reward trial compared to placebo, meaning that those who took green tea showed a significantly increased reward learning. In addition, individuals who took the green tea had a reduction in the MADRS and HRSD-17 scales demonstrating improvement in depression, when compared with placebo group.
These findings suggest that reduced reward learning might be associated with depression. The regulatory role of green tea on the reward learning raises the possibility that it may be a supplemental treatment in reversing depression via its ability to normalize the reward function.
Commentary: Other studies have demonstrated that regular intake of green tea could reduce depressive symptoms. There is also evidence that a disturbance in reward learning can be associated with anhedonia, a frequent core symptom of depression and a requirement, along with depression for a diagnosis of major depressive disorder. The definition of anhedonia, per The American Psychological Association is feeling less interest in hobbies, apathy, and lack of enjoyment in activities that were previously enjoyed. Past research has linked dopamine deficiency and the reduction of dopamine transmission with anhedonia. Even though conventional medications address many depressive symptoms, it seems these do not adequately address motivation and reward deficits in depression. It has been proposed that the active components in green tea, EGCG, work in part by modulating dopamine transmission.
Zhang Q, Yang H, Wang J, et al. Effect of green tea on reward learning in healthy individuals Nutrition Journal 2013; 12:82 2013