It proved too tedious & difficult a task to track down the scientific reports via Google & the public web, starting with only press reports as a lead.
One interesting fact to emerge from the work I did manage to do was that very few of these studies actually involved coffee. For example one involved giving caffeine to laboratory rats, another gave cola drinks to a group of psychology undergraduates.
But caffeine is caffeine, seems to be the line; & scientists - or journalists - always like to make the results relevant to the daily lives of readers of non-specialist journals by using the handy equivalent of a number of cups of coffee which, mysteriously or suspiciously, turns out usually to be three per day.
However a recently reported study was very specific in ruling out other sources such as tea or chocolate or cola, in helping to prevent depression.
However in this case you need 4 or more cups a day to gain the greater benefit..
At least if you are an American nurse (whose cups are smaller than ours)
Methods A total of 50 739 US women (mean age, 63 years) free of depressive symptoms at baseline (in 1996) were prospectively followed up through June 1, 2006. Consumption of caffeine was measured from validated questionnaires completed from May 1, 1980, through April 1, 2004, and computed as cumulative mean consumption with a 2-year latency period applied. Clinical depression was defined as self-reported physician-diagnosed depression and antidepressant use. Relative risks of clinical depression were estimated using Cox proportional hazards regression models.
Results During 10 years of follow-up (1996-2006), 2607 incident cases of depression were identified. Compared with women consuming 1 or less cup* of caffeinated coffee per week, the multivariate relative risk of depression was 0.85 (95% confidence interval, 0.75-0.95) for those consuming 2 to 3 cups per day and 0.80 (0.64-0.99; P for trend <.001) for those consuming 4 cups per day or more.
*Note to pedants: this is a mathematically precise term
Link
Related post
Without links
Three Cups of Coffee a day Good for Your Brain
Three Cups of coffee a day to help keep skin cancer away
Three cups of coffee a day makes breasts shrink
The caffeine intake from three cups of coffee a day can reduce the risk of developing ovarioan cancer
Men who drink three cups of coffeee a day have 40 per cent lower risk of developing gallstones
Coffee drinkers who have more than three cups of coffee a day may increase their risk of heart attack
