Excessive alcohol consumption is a major cause of health problems throughout the Western world, and the need for objective clinical tools for detecting alcohol abuse in its early phase has been widely acknowledged. Gamma-glutamyl transferase (GGT) is a liver-derived enzyme, which has long been used as a marker of excessive alcohol consumption, but the amount of drinking needed to elevate GGT levels has remained unknown. Also, it has been suggested that GGT levels may be elevated by factors such as obesity and increasing age in addition to alcohol consumption, although the magnitude of such effects have remained unclear.

The relationships between alcohol consumption, obesity, age and GGT values are studied here in a large number of heavy drinkers and apparently healthy reference individuals, classified as fol-lows: subjects reporting no alcohol consumption (abstainers), subjects reporting 1­40 grams of ethanol consumed per day (moderate drinkers) and subjects reporting 40-­540 grams of ethanol con-sumed per day (heavy drinkers). The reference population was further classified according to body mass index (BMI) into underweight (BMI30), and by age into those under 18 years, 18-­30 years, 3-0­50 years, -50­70 years and over 70 years.

GGT activity was markedly higher in the heavy drinkers than in the moderate drinkers (p The data show that serum GGT is a highly sensitive indicator of ethanol consumption, although its diagnostic value could be improved by using reference data based solely on abstainers of normal weight, or else BMI-specific reference intervals. Also, the fact that GGT activity responds to etha-nol in an age-dependent manner should be considered in the clinical use of GGT measurements for detecting alcohol consumption disorders.