Coffee consumption, serum γ-glutamyltransferase and risk of type II diabetes

Objectives: To study the joint association of coffee consumption and serum gamma-glutamyltransferase (GGT) levels on the risk of developing type II diabetes. Design, setting and subjects: A total of 21 826 Finnish men and women who were 35-74 years of age and without any history of diabetes at baseline (years 1982, 1987, 1992 and 1997) were included in the present analyses. They were prospectively followed up for onset of type II diabetes (n = 862 cases), death or until the end of the year 2002. Coffee consumption, serum GGT and other study parameters were determined at baseline using standardized measurements. Analyses were stratified by the serum GGT level classified into two classes using the 75th sex-specific percentiles as the cut point. Results: Coffee consumption was significantly and inversely associated with incident diabetes among both men and women. Serum GGT modified the association between coffee consumption and incident diabetes. Subjects in the high category of coffee consumption with the GGT level >= 75th percentile showed a significant inverse association for women, and for both sexes combined. The association was not significant in subjects with the GGT level <= 75th percentile. There was a significant interaction effect of GGT and coffee consumption on risk of type II diabetes in data of women (P = 0.05) and in both sexes combined (P = 0.02). Conclusions: Habitual coffee consumption is associated with lower incidence of type II diabetes particularly in those with higher baseline serum GGT levels.