Effects of long-term moderate alcohol consumption on agonistic and affiliative behavior of socially housed female cynomolgus monkeys (Macaca fascicularis)

Rationale: The most widely used drug in the US is alcohol. Most people who use alcohol are light-to-moderate drinkers. One or two drinks/day is thought to be not only safe but potentially health-promoting. However, little is known about the chronic effects of moderate alcohol consumption. Alcohol, even in moderate doses, has immediate and robust effects on behavior. Objective: To determine the effects of long-term moderate alcohol consumption on the social interactions of adult monkeys. Methods: Forty-nine adult, ovariectomized monkeys lived in small, stable social groups for 31 months and voluntarily consumed a 2-drink/day equivalent (0.5 g/kg ethanol), 5 days/week for 24 months. Alcohol was presented in a sweet tasting non-nutritive vehicle to half the monkeys, while the other half received vehicle plus maltose-dextrin isocalorically substituted for alcohol. Social behavior was recorded 1 h before, 1 h after, and 5 h after alcohol. Results: Alcohol caused chronic changes in aggressive and affiliative behavior that were not dependent upon the presence of circulating alcohol. Alcohol increased physical aggression. A subset of the animals was at higher risk for alcohol-induced physical aggression. Alcohol decreased positive affiliative behaviors, increased time spent alone, and increased the frequency of extragroup vigilance. Acutely, alcohol increased the rate of behavioral pathology, i.e. stereotypic behaviors, such as hair plucking, which are normally observed only under adverse environmental conditions. Conclusions: Long-term moderate alcohol consumption caused chronic deleterious changes in the social interactions of primates in small, stable social groups. These data suggest that chronic moderate alcohol consumption can compromise optimal social interactions in primate species, including human beings.