Background. Attention has long been drawn to the potentially harmful effects of coffee on health, however recent epidemiological studies have suggested unexpected, possibly beneficial effects of coffee against the occurrence of alcoholic liver cirrhosis and upon serum liver enzyme levels. Methods. We examined the potential inverse association between coffee drinking and serum concentrations of gamma-glutamyltransferase (GGT) and aminotransferases, with special reference to interaction with alcohol consumption, in a cross-sectional study involving 12,687 health examinees (7398 men and 5259 women) aged 40-69 years from over 1000 workplaces in Nagano prefecture in central Japan. Those who had a history of liver disease and/or serum aminotransferases exceeding the normal range were excluded. Possible confounding effects of alcohol consumption, body mass index, cigarette smoking, and green tea consumption were controlled through multivariate analyses. Results. Increased coffee consumption was strongly and independently associated with decreased GGT activily among males (P trend < 0.0001); the inverse association between coffee and serum GGT was more evident among heavier alcohol consumers (P < 0.0001), and was absent among non-alcohol drinkers. Among females, however, coffee was only weakly related to lower GGT level. Similar inverse associations with coffee and interactions between coffee and alcohol intake were observed for serum asparate aminotransferase and alanine aminotransferase. Intake of green tea, another popular source of caffeine in Japan, did not materially influence the liver enzyme levels. Conclusions. Our results suggest that coffee may inhibit the induction of GGT in the liver by alcohol consumption, and may possibly protect against liver cell damage due to alcohol.
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