An Introduction to Alcohol and Anxiety Disorders
The link between the consumption of alcohol, and the complexity of neurobiological pathways that underlie the susceptibility to both anxiety disorders and to alcohol dependence, is a complex interaction dominated by dysregulated stress responses. There are common pathways to both disorders through chronic stress and a familial vulnerability for alcohol problems, each affecting the other. The central amygdala, a brain area critical for fear responses, is involved in both anxiety and alcohol use disorders. When twenty-five years ago researchers sought “the alcoholism gene” they found instead a network of genes coding for an especially intense anxiety (fight/flight) response.
Those with anxiety disorders experience a ‘faster time to substance dependence,’ supporting the ‘telescoping’ hypothesis. In other words, alcohol provides relief of an ever-present tension seen only in those with severe anxiety responses, a tension followed by relief that those without such responsivity do not appreciate.
Targeting biological stress reactivity in treatments for alcohol use disorder helps address the complex interrelationships between alcohol, anxiety, and stress regulation.
Understanding the Connection Between Anxiety and Alcohol
Individuals with high stress reactivity learn intuitively to consume alcohol to “self-medicate” anxiety. This tactic elevates the risk of progression to formal Alcohol Use Disorder (AUD, e.g., alcoholism). The transition from anxiety to addiction underscores the fact that it is of critical importance to develop more holistic treatment strategies for these co-morbid disorders. AUD investigators are increasingly turning their attention to biological stress reactivity, in hopes of unearthing in greater specificity the biological relationship between alcohol and anxiety.
The Genetic Grounding of Anxiety and Alcoholism
Research has shown that heredity accounts for approximately 50-60% of the likelihood of developing alcoholism. Various stages of the addiction cycle have been associated with particular genetic variants in genes such as NPY, OPRM1 , and BDNF, once again reflecting the multifactorial nature of genetic contributions to both alcoholism and anxiety. In research, it is essential to focus on which genetic variants are contributing to these illnesses—one size does not fit all.
An Evolutionary Genetics View
The development of a rapid and intense stress response system, including the fight-or-flight reflexes mediated by the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis, was a crucial aspect of survival in ancestral environments. Genetic variation affecting this system would have led to individual differences in the ability to deal with stress. Individuals with an exaggerated stress response would have been more likely to survive and reproduce in environments that were pervasively hostile. However, such heightened sensitivity presents as unwarranted anxiety in modern times. Alcohol and other substances of use can temporarily dampen this response, thus their potential for misuse.
Reward Pathways
The brain’s reward pathways, particularly those involving dopamine, evolved to reinforce behaviors that were essential for survival, for example defense and procreation. The differing genetic makeup of the pathways that once increased the chance of survival, however, may now be contributing to anxiety disorders and the overuse of alcohol.
North-South Gradient: Adaptation to Environmental Extremes
The genetic makeup of northern populations that endured extreme cold and darkness would have included adaptations that affect metabolism and energy storage. These changes would affect the metabolism of substances such as alcohol, one impact of which would have been an influence on tolerance or dependence.
Southern populations that inhabited hotter, sunnier areas of the world would have evolved a different set of adaptive needs. These genetic differences would come into play by altering how different populations metabolize alcohol and by how anxious they become. They could also influence the prevalence of alcohol use and abuse.
Migration and Gene Flow:
As human populations migrated they encountered disparate environments that subjected them to various new selective pressures; these led to further genetic changes. Gene flow among populations—i.e., the movement of genetic material—would move these new changes around and create different gradients of genetic traits that include susceptibility to diseases. On the other hand, the ever-increasing admixture of genes, characteristic of the modern world, has attenuated these ancient genetic influences.
It’s essential to note that these are theoretical considerations from an evolutionary genetic viewpoint, and that the specific genetic influences on the comorbidity of alcoholism and anxiety disorders is expected to be polygenic and multifactorial. In addition, current understanding of these complex traits in their genetic context is incomplete, and other factors like environment, culture, and individual experience are significant contributors to their expression.
The concept of a residue of evolutionary genetics is that modern humans emerged from a distant past, and while they are not shaped by the selective pressures of ancestral environments, they continue to carry the imprints of their earlier conditions—imprints that unevenly affect their vulnerability to certain conditions, such as the comorbidity of alcoholism and anxiety disorders. These displays may differ along a North-South gradient since the relatedness of historical population adaptations were for different climates and ways of life.