Combined effects of coffee consumption and serum γ-glutamyltransferase on serum C-reactive protein in middle-aged and elderly Japanese men and women.

Background: The association between coffee intake and circulating levels of C-reactive protein (CRP) may be modified by oxidative stress. The authors examined the relation of coffee consumption to serum CRP considering potential interactions of serum g-glutamyltransferase (GGT) and bilirubin. Methods: The subjects included 4455 men and 5942 women aged 49-76 years who participated in the baseline survey of a cohort study on lifestyle-related diseases in Fukuoka, Japan. Geometric means of serum CRP and 95% confidence intervals across the category of coffee intake stratified by serum GGT and bilirubin were estimated using multiple linear regression. Results: Serum CRP concentrations were progressively lower with higher intake of coffee in men with high serum GGT (p for trend=0.009), but not in those with low serum GGT (p for trend=0.73) and GGT modified the association (p for interaction=0.03). Women showed no association between coffee intake and CRP whether serum GGT was low or high. There was no effect modification of serum bilirubin on the association between coffee intake and CRP in either men or women. Conclusions: These results support a protective effect of coffee intake against systematic inflammation in middle-aged and elderly Japanese men and imply that such an effect may be stronger in elevated oxidative stress.