In January 2016 researchers from Poland published a review of the scientific literature to assess the effect of coffee, caffeine, and tea consumption on the risk of depression. Twelve studies involving 346,913 individuals and 8,146 diagnoses of depression were included in the analysis. Results showed that individuals who consumed coffee had a reduced risk of depression. However, the protective effect of coffee appeared to peak at 400 mL/day. There was only a borderline association between tea consumption and risk of depression which became more significant when the caffeine content was analysed. The researchers therefore concluded that coffee reduced the risk of depression, more so than tea or caffeine.
Grosso G et al. Coffee, tea, caffeine and risk of depression: A systematic review and dose-response meta-analysis of observational studies. Mol Nutr Food Res. 2016 Jan;60(1):223-34.