Age of alcoholism onset. II. Relationship to susceptibility to serotonin precursor availability

Alcoholics who start abusing alcohol early in life have been found to exhibit problems with mood and aggression control more frequently than patients with a later onset of alcoholism. Because alcohol preference and consumption, as well as mood and aggression regulation, are believed to be influenced by serotonin, relationships between tryptophan availability and mood and aggression regulation were explored in alcoholics. When studied in the entire population, the ratio of tryptophan over other amino acids competing for brain entry (which influences brain serotonin) was found to be lowest one day after cessation of drinking and to increase progressively over the following two to three weeks. When the population was divided into two groups of patients according to whether subjects started abusing alcohol before or after 20 years of age, associations between a low tryptophan ratio and depressive and aggressive tendencies were significant only in the subgroup of patients with an early onset of alcoholism. They were not significant in the rest of the population. Our data are compatible with the interpretation that patients with an early onset of alcoholism have a preexisting serotonin deficit that could manifest itself by an increased alcohol intake early in life and by an increased vulnerability to fluctuations in precursor availability.