What Causes Addiction: Part 2, Nurture

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David Fawcett PhD

In my previous post, I introduced the idea that there are two primary risk factors for addiction: nature and nurture. In last week’s post, the discussion focused on nature (genetics). This week, I will look at the impact of nurture (environmental factors).

Nurture (Environment)

Addiction is not entirely the fault of genetics. How we were raised and how we experienced life, especially during childhood, can be equally and perhaps more impactful. This fact that has repeatedly been proven by research, primarily by studying the incidence of addiction among adopted children and twins, especially monozygotic (identical) twins separated at birth and raised by different parents. By studying these populations, the relative influence of genetics and environment can be separated and measured.

The most basic studies linking nurture and addiction examine what happens to children of addicts if they’re adopted into a non-addicted family. Generally, findings indicate that these children are more likely than normal to develop an addiction,[i] which suggests a genetic link to addiction. But plenty of these kids do not become addicted, which suggests that environmental influences can override genetics.

Studies of twins, both dizygotic (fraternal) and monozygotic (identical), tend to be even more enlightening. Research consistently tells us that both twin types show a common risk toward addiction.[ii] If one twin is addicted, the risk for addiction is significantly increased for the other, with the correlation greater for monozygotic than dizygotic twins. But again, the risk is not set in stone. There are plenty of cases where one twin is addicted and the other is not, especially if they were raised separately. So again, it appears that environment plays a significant role.

One of the most common and easily identified environmental risk factor for addiction is early exposure to an addictive substance or behavior. Stated very simply, the earlier one experiments with an addictive substance or behavior, the higher the likelihood that one will become addicted.[iii] And this is true with all forms of addiction.

Childhood Trauma (ACES)

Without question, the most consequential environmental factor in the risk for addiction is childhood trauma, sometimes referred to by therapists as ACES (Adverse Childhood Experiences). There are ten categories of ACES, split into personal traumas and familial traumas.

Personal traumas:

  • Physical abuse
  • Verbal abuse
  • Sexual abuse
  • Physical neglect
  • Emotional neglect

Familial traumas:

  • Addiction
  • Domestic violence
  • Incarcerated family member
  • Mental illness
  • Divorce or abandonment

Studies have consistently linked ACES to all kinds of later-life physical, emotional, and relational issues, including all categories of addiction. The more adverse experiences a child has, the more likely he or she is to have problems as an adult, everything from physical ailments like heart disease, cancer, and diabetes, to emotional and behavioral ailments like depression, anxiety, and addiction. One large-scale study found that individuals with four or more adverse childhood experiences are:

  • 1.8 times as likely to smoke cigarettes
  • 1.9 times as likely to become obese
  • 2.4 times as likely to experience ongoing anxiety
  • 2.5 times as likely to experience panic reactions
  • 3.6 times as likely to be depressed
  • 3.6 times as likely to qualify as promiscuous
  • 6.6 times as likely to engage in early-life sexual intercourse
  • 7.2 times as likely to become alcoholic
  • 11.1 times as likely to become intravenous drug users[iv]

Thus, there is an undeniable link between early-life traumatic experiences (neglect, abuse, bullying, major life events of a negative nature, etc.) and countless adult-life physical and psychological disorders, including addictions.

Sometimes the age of first exposure to an addictive substance or behavior and adverse childhood experiences are directly related, as addictive substances and/or activities can be readily available within a dysfunctional home environment, and early exposure to those substances and behaviors, especially sexual behaviors, can be highly traumatic. In such cases, environmental risk factors beyond just age of first exposure, such as abuse, neglect, inconsistent parenting, and other ACES, may be the overarching factor in the development of addiction.

Addition Risk: A Witch’s Brew

Based upon considerable amounts of research, it is clear that addiction arises based on a number of risk factors. Moreover, those risk factors tend to intertwine and build upon one another. It is equally clear that, for whatever reason, some people appear to be more resilient and therefore less likely to become addicted than others. For instance, a combination of genetic predisposition, addicted parents, various forms of childhood trauma, and even early exposure to an addictive substance or behavior occurs fairly often in our society. With this combination, the risk for addiction (and numerous other adult-life disorders, both physical and psychological) is increased. But such problems are not mandatory. A witch’s brew of risk factors is not an automatic life sentence. Some (perhaps most) people who drink this particular potion will struggle, but plenty of others will not.

Either way, at the end of the day the conversation about the cause of someone’s addiction is less an argument about nature vs. nurture and more an examination of how various risk factors, both genetic and environmental, come together to influence an individual’s thinking and behaviors.

References

[i] Sigvardsson, S., Bohman, M., & Cloninger, C. R. (1996). Replication of the Stockholm Adoption Study of alcoholism: Confirmatory cross-fostering analysis. Archives of General Psychiatry, 53(8), 681-687, and, Goodwin, D. W. (1979). Alcoholism and heredity: A review and hypothesis. Archives of General Psychiatry, 36(1), 57-61, among other studies.

[ii] Agrawal, A., & Lynskey, M. T. (2008). Are there genetic influences on addiction: evidence from family, adoption and twin studies. Addiction, 103(7), 1069-1081, and, Heath, A. C., Bucholz, K. K., Madden, P. A. F., Dinwiddie, S. H., Slutske, W. S., Bierut, L. J., … & Martin, N. G. (1997). Genetic and environmental contributions to alcohol dependence risk in a national twin sample: consistency of findings in women and men. Psychological medicine, 27(06), 1381-1396, among other studies.

[iii] DeWit, D. J., Adlaf, E. M., Offord, D. R., & Ogborne, A. C. (2000). Age at first alcohol use: a risk factor for the development of alcohol disorders. American Journal of Psychiatry, 157(5), 745-750, and, Grant, B. F., Stinson, F. S., & Harford, T. C. (2001). Age at onset of alcohol use and DSM-IV alcohol abuse and dependence: a 12-year follow-up. Journal of substance abuse, 13(4), 493-504, among other studies.

[iv] Anda, R., Felitti, V., Bremner, J., Walker, J., Whitfield, C., Perry, B., … Giles, W. (2006). The enduring effects of abuse and related adverse experiences in childhood. European Archives of Psychiatry and Clinical Neuroscience, 256(3):174-186.