In February 2014 researchers from the USA published their review of the scientific literature to assess the association between coffee consumption and the risk of type 2 diabetes. Twenty-eight studies were included in the analysis, and involved 1,109,272 participants and 45,335 cases of type 2 diabetes. The period of follow-up ranged from 10 months to 20 years. Results showed that the risk of type 2 diabetes decreased with each 1 cup/day increment in the amount of caffeinated and decaffeinated coffee consumed.
Ding M et al. Caffeinated and decaffeinated coffee consumption and risk of type 2 diabetes: a systematic review and a dose-response meta-analysis. Diabetes Care. 2014 Feb;37(2):569-86.