Coffee consumption, serum γ-glutamyltransferase, and glucose tolerance status in middle-aged Japanese men

BACKGROUND: Recently, coffee consumption has been related to decreased risk of type 2 diabetes mellitus (DM) among those with high levels of serum γ-glutamyltransferase (GGT). We examined the association between coffee and glucose tolerance, determined by a 75 g oral glucose tolerance test, and the effect modification of serum GGT on the association. METHODS: The study subjects were 5320 men aged 46-60 years who received a health examination at two Self-Defense Forces hospitals from January 1997 to March 2004. Those medicated for DM were excluded. Coffee consumption was classified into 40 IU/L) GGT groups, and for combined IFG/IGT and type 2 DM in the latter group. CONCLUSIONS: Coffee drinking is protective against glucose intolerance. A possible effect modification of GGT on the coffee-DM association warrants further studies.