Q Is it true that Coffee improves Concentration?
A There’s no denying the lift and the buzz you get from a cup of good coffee. Scientists have backed this up with research that showed two cups of coffee give you maximum alertness and concentration – but this is only short term, as over time you need more and more to get the same effect. In other words, you’re addicted.
Another study concludes that the benefits of coffee are at best meagre when you consider the negative effects of caffeine withdrawal, and that overall drinking coffee causes a decline in performance and health . Research on 1,500 psychology students showed that those who drank more coffee had higher levels of anxiety, depression and stress-related medical problems, and lower academic performance. So, all in all, I would say that the short-lived up from a cup of coffee is not worth the down side as far as your health and mental well-being are concerned.
References  Quinlan PT, Lane J, Moore KL, Aspen J, Rycroft JA, O'Brien DC. The acute physiological and mood effects of tea and coffee: the role of caffeine level. Pharmacol Biochem Behav. 2000 May;66(1):19-28. PubMed PMID: 10837840.  Rogers PJ, Heatherley SV, Hayward RC, Seers HE, Hill J, Kane M. Effects of caffeine and caffeine withdrawal on mood and cognitive performance degraded by sleep restriction. Psychopharmacology (Berl). 2005 Jun;179(4):742-52. Epub 2005 Jan 26. PubMed PMID: 15887055.