Earlier quoted context omitted.
There are probably a number of causes, but coffee may be one of them. Don't be radical, but if you're having too much coffee, I'd suggest cutting down to just one coffee in the morning. It will take a bit of effort but may help you concentrate. I'd suggest gradually cutting down to none. Apparently the alertness and general cognitive enhancing properties of caffeine don't really exist and all that people are noticing…
This is clearly unsubstantiated - the benefits of coffee are very clearly outlined. Maybe some people who drinks too much are experiencing the withdrawal, but if you do not over-do it, there is a 90% chance of feeling more alert when you drink coffee.
No, what we know about benefits of caffeine is quite weak.
http://www.evidentlycochrane.net/caffeine-and-health-evidenc...