Many studies have found an inverse association between consumption of filtered coffee and incident type 2 diabetes. The effect of boiled coffee has been less studied.
Information on self-reported coffee consumption was available from health surveys conducted from 1985 to 1999. We estimated type 2 diabetes incidences from redeemed prescriptions of oral antidiabetic drugs in the period 1 January 2004 to 1 January 2008.
With less than 1 cup/day as the reference, the relative risks associated with 1-4, 5-8, and 9 or more cups of boiled coffee per day were 0.87 (95% confidence interval = 0.80-0.95), 0.65 (0.59-0.72), and 0.65 (0.57-0.74), respectively, after adjusting for confounders. The corresponding relative risks associated with other types of coffee (mainly filtered) were 0.84 (0.79-0.90), 0.67 (0.62-0.71) and 0.62 (0.56-0.68).
A moderate inverse association was found between consumption of both boiled and other types of coffee at the age of 40-45 years and the risk of being prescribed oral antidiabetic drugs 5-20 years later.