...and the relationship between caffeine consumption and depression remain controversial, here are some relevant findings:
The Royal Australian and New Zealand College of Psychiatrists conducted a meta-analysis with a dose-response analysis to quantitatively summarize the evidence about the association between coffee and caffeine intakes and risk of depression.
METHOD:
Relevant articles were identified by researching PubMed, Web of Science, China National Knowledge Infrastructure and WANFANG DATA in English or Chinese from 1 January 1980 to 1 May 2015. Case-control, cohort or cross-sectional studies evaluating coffee or caffeine consumption and depression were included.
A random-effects model was used to combine study-specific relative risk and 95% confidence interval. Dose-response relationship was assessed by restricted cubic spline functions.
RESULTS:
Data were obtained from 11 observation articles; 330,677 participants from seven studies in seven articles were included in the coffee-depression analysis, while 38,223 participants from eight studies in seven articles were involved in the caffeine-depression analysis.
Compared with the lowest level consumption, the pooled relative risk (95% confidence interval) for coffee-depression and caffeine-depression was 0.757 [0.624, 0.917] and 0.721 [0.522, 0.997], respectively.
For dose-response analysis, evidence of a linear association was found between coffee consumption and depression, and the risk of depression decreased by 8% (relative risk = 0.92, 95% confidence interval = [0.87, 0.97], p = 0.002) for each cup/day increment in coffee intake; a nonlinear association was found between caffeine consumption and depression, the risk of depression decreased faster and the association became significant when the caffeine consumption was above 68 mg/day and below 509 mg/day.
Coffee and caffeine consumption were significantly associated with decreased risk of depression. While this does offer encouraging results, further investigation is needed to understand the relationship between depression and coffee or caffeine intake.