A review of nine studies looking at a total of 193,437 regular coffee drinkers found that people who drank 4-6 cups of coffee per day had a 28% lower risk of type 2 diabetes than those who drank fewer than 2 cups per day.  People who drank more than 6-7 cups per day had a 35 percent lower risk.  Researchers are not sure exactly how the coffee cuts diabetes risks, but they suspect the antioxidants or magnesium found in coffee might be the reason.  Another study of 2,000 women done by Harvard found that concentrations of C-peptide (proteins that are linked to type 2 diabetes) decreased significantly in both decaf and regular coffee drinkers.

Sources:  JAMA, July 2005; Diabetes Care, June 2005