Fahlke, C., Lorenz, J.G., Long, J., Champoux, M., Suomi, S.J., & Higley, J.D. (2000, May). Rearing experiences and stress-induced plasma cortisol as early risk factors for excessive alcohol consumption in nonhuman primates. Alcoholism: Clinical and Experimental Research, 24(5), 644-650.
Stress is known to influence drinking behavior. Research indicates that people drink as a way to cope with economic stress, job stress, marital problems, and in the absence of social support. The more severe and chronic the stressor, the greater the alcohol consumption. A study in the May issue of Alcoholism: Clinical & Experimental Research has found a link among the rearing environment (how a child is raised), sensitivity to stress, and subsequent alcohol consumption.
"It’s pretty clear that parents are the crucial role models and crucial shapers of their offspring’s behavior," said J. Dee Higley, research psychologist at the National Institute of Child Health and Human Development and lab director of the experiment. "Adults are very good at helping youngsters to understand that ‘this is dangerous, this is not dangerous.’ In the absence of that kind of adult influence, children don’t have any kind of certainty about what to fear or enjoy, what is good or bad. Adults are also very good at cueing into whether their offspring are aroused or anxious, and then helping them to calm themselves down."
Higley’s study looked at rhesus monkeys, which share between 90 to 95 percent of their genetic material with humans. These monkeys also have a similar adrenal system which, for the purposes of this study, means that they respond to stress like humans do. In addition, primates have very complex societies; they create social groups, they have rules about social behavior, and they are (under normal circumstances) trained from youth to learn and use appropriate social skills. The monkeys used in this study were part of an ongoing longitudinal study investigating genetic and environmental influences on neurobiology, behavior, and alcohol consumption.
The monkeys were divided into two groups for the first six months of their lives. The first group was "peer-reared," meaning that group members were raised without the presence of their mothers or other adults, but surrounded by same-aged peers. Members of the second group were raised normally, in the presence of their mothers. At six months of age, all of the monkeys were separated from their groups for portions of a four-week period. Stress levels were assessed during this time by examining concentrations of cortisol, a principal stress hormone. At 50 months of age (roughly equivalent to young adulthood), the monkeys were allowed access to alcohol for five to seven weeks.
"This study very clearly showed that early life experiences can have a dramatic effect on subsequent development of alcohol consumption," noted Larissa A. Pohorecky, professor of neuropharmacology at the Center of Alcohol Studies, Rutgers University. "It helps elucidate the mechanisms involved in stress/alcohol interaction." She added that most of the other alcohol research, including her own, has focussed on rodents. "So these are particularly important findings because these primates are the closest animal species to humans," she said.
The study found that infant monkeys from both groups, peer-reared and mother-reared, were stressed by their separation from the group (as evidenced by cortisol concentrations), although the peer-reared monkeys more so. In addition, those infant monkeys (from both groups) who were highly stressed as a result of their group separation later consumed more alcohol (as young adults) than their less-stressed peers did. Higley says these results have two important implications.
"First, we may have found a biological marker," he said, " which can be obtained very early in life and may predict future alcohol consumption. This is probably the strongest marker we’ve found so far in the non-human primate that predicts alcohol consumption." He added that, "to the extent that this can be generalized to humans, we may have identified a biological predictor of future alcohol problems."
Higley said the second implication is that "early-rearing experiences that increase anxiety – as measured by cortisol output - also increase subsequent alcohol consumption." In this experiment, separation from the group was what induced stress, but the monkeys’ peer-rearing environment may have ‘set them up’ for experiencing a greater level of stress. "The peer-reared monkeys had all the opportunities to socialize that mother-reared monkeys did - they could play with other-aged mates, form strong friendships, they could even fight, they could do all sorts of socially appropriate and inappropriate things - but what was lacking in their environment was an adult," explained Higley. "These monkeys showed emotional instability, they were more fearful, they were much more reactive to the stimuli around them, and they did not have an adult around to calm them down. So what you have is a monkey who is chronically anxious and chronically fearful."
Adult absence during infancy appears to have had other long-term psychobiological consequences, noted Higley. "As young teenagers, the peer-reared monkeys still showed infant-like fearfulness and anxiety that was absent in the mother-reared monkeys." Indeed, other studies have found that prolonged stress in infancy (and a peer-rearing environment among monkeys is regarded as a stressor) may permanently alter the hormonal stress response and subsequent reactions to new stressors.
Pohorecky believes the study’s results are relevant to the role played by parents, as well as their presence, in their children’s lives. "These findings speak to the importance of how society handles children who have problems, families with parenting problems, general parenting issues, orphans, to name a few," she said. "We may not be paying enough attention to the importance of parenting roles, and how that can affect their children’s lives."