In March 2016 researchers from China published their review of the scientific literature to assess the association between coffee and caffeine intake and risk of depression. 330,677 individuals from seven studies were included in the coffee-depression analysis and 38,223 participants from eight studies in the caffeine-depression analysis. Results showed that for each cup of coffee per day the risk of depression decreased by 8%. It was also seen that the risk of depression decreased faster when caffeine consumption was above 68 mg per day but below 509 mg per day.
Wang L et al. Coffee and caffeine consumption and depression: A meta-analysis of observational studies. Aust N Z J Psychiatry. 2016 Mar;50(3):228-42