Addiction: Nature versus NurtureTwo Kids, One Bottle, Vastly Different Response

Best friends Eric and Thomas are 14 years old. They are from upper-middle-class families. They make good grades, play sports, and are getting interested in girls. At their eighth grade graduation Thomas tells Eric that his older brother has invited them to an end-of-school party. They know they’re only being invited so Thomas won’t rat on his brother for being at a party where kids are drinking, but they don’t care because they’re invited to their first-ever high school party. As a further inducement to silence, Thomas receives a bottle of rum from his older sibling.

Before going to the party, Eric and Thomas decide they should each have a drink. They crack open the bottle and fill two water glasses with half rum, half Coke. They’ve heard that rum and Coke go together, and this seems like the “adult” way to drink it – even though the concoction both smells and tastes like sugar-infused antiseptic. Eric sips half the glass, starts to feel lightheaded, and decides he’s had enough. Thomas, however, drinks his entire serving. Before they leave the house, he slogs the remainder of Eric’s cocktail too. By the end of the night, he’s finished half the bottle, made a bunch of new friends, kissed a high school girl, and thrown up in someone’s yard. A day later, despite his throbbing headache, he’s eager to do it all over again.

So why is Eric able to satisfy his curiosity about alcohol and stop, when Thomas is out-of-control from almost the first sip?

This, of course, is the age-old question about alcoholism and other addictions. Simply put, nearly everyone in modern western culture tries alcohol at some point in his or her life, but only a small percentage actually become alcoholic. The same is true with other potentially addictive drugs and behaviors: many partake, but only a few become addicted. Why is it that some people can “just say no” while others cannot? Surely there must be some obvious, easily spotted difference between “healthy” people and addicts, some telltale giveaway? But to date there is not. In fact, Eric and Thomas are so much alike they’re practically twins. They live in the same neighborhood, they take the same classes, they earn the same grades, they play the same sports, they wear the same clothes, they have the same haircut, and they hang out with the same kids. From outward appearances, there is no way to know that one boy is predisposed to addiction while the other is not.

The Hangover, Part 1,546 (and Counting)

It is clear that people start and continue using potentially addictive substances and behaviors because those substances and behaviors reward them with a pleasure response in the brain. (This is true for both addicts and non-addicts.) In short, potentially addictive substances and behaviors cause the release of various neurotransmitters (primarily dopamine, but also oxytocin, serotonin, and a few others) into the nucleus accumbens – also known as the brain’s “pleasure center” or “rewards center.” Typically, addictive substances and behaviors flood the pleasure center with two to ten times more dopamine than natural reward-triggering activities (such as spending time with a loved one, helping a friend in need, eating a healthy meal, etc.) This, of course, is a pretty big boost in the feel-good department, so it’s easy to see the appeal.

This information is good to know, of course, because it makes clear the idea that artificially elevated dopamine levels are a pathway into addiction. Unfortunately, this understanding doesn’t explain why some people become addicted while others do not. After all, if the brain’s pleasure response is all there is to addiction, then everyone who’s ever had a sip of rum would automatically become alcoholic. Clearly that is not the case, so other factors must be in play.

Are Addicts Genetically Doomed?

Dozens of studies have shown a significant link between genetics and the risk for addiction. This research has found that certain genetic mutations directly increase or decrease the risk for addiction, usually by altering the ways in which a particular substance is experienced in the body/brain. For instance, scientists have found that a genetic mutation reducing the amount of body sway after drinking alcohol correlates directly with alcoholism; those who are genetically less susceptible to alcohol’s effects on balance and coordination tend to drink more. In other words, drinkers who don’t fully experience the potential side effects of alcohol can consume more (get higher) without falling down, getting sick, or passing out, and they are, as a result, more likely to drink heavily. Other studies reveal a second genetic variation that increases the risk for alcoholism. Essentially, a particular variant of the dopamine D2 receptor gene magnifies the pleasurable effects of alcohol. Sadly, individuals with this genetic mutation are ten times more likely than others to experience a premature alcohol-related death.

In similar fashion, genetics can also reduce the risk of alcoholism. For instance, it has long been known that people of East Asian ancestry are much less likely than other ethnic groups to become alcoholic, and scientists now know why. In short, they’ve identified a genetic mutation that causes a deficiency of the aldehyde dehydrogenase enzyme, which is critical to the metabolism of alcohol. This means that when alcohol is consumed by people with this genetic mutation, classic hangover symptoms (headache, dehydration, nerve and tissue sensitivity, rapid heartbeat, nausea, and the like) occur almost immediately. In other words, alcohol makes these folks physically ill instead of getting them high. Needless to say, alcoholism is incredibly rare among people with this genetic mutation.

Genetic factors can also contribute to addiction indirectly. For instance, genetics are a factor with numerous psychiatric disorders (depression, anxiety, attention deficits, panic disorders, bipolar disorder, social phobia, etc.) Not surprisingly, many people living with these disorders choose to self-medicate with alcohol, drugs, or an addictive behavior. In such cases, what is genetically inherited is not a unique response to a potentially addictive substance or behavior, but the propensity for an underlying neurobiological vulnerability that may, over time, lead to addiction. For instance, half of all people diagnosed with bipolar disorder have also been diagnosed with a substance use disorder. Their increased risk for addiction has little to do with the way addictive substances and behaviors are experienced in the body; instead, it’s connected to a desire to escape and dissociate from uncomfortable emotions, life stressors, and the pain of an underlying, genetically driven psychiatric disorder.

Another example of the indirect effect of genetics on addiction is seen when we examine certain heritable personality traits such as impulsivity and novelty seeking, which appear to significantly increase the risk for addiction. In short, the predisposition toward rapid, unplanned actions without regard to potential negative consequences is closely associated with both substance abuse problems and behavioral addictions. Here, it is an inherited pattern of impulsiveness that causes dangerous behaviors, one of which may be engagement with potentially addictive substances and/or behaviors. Again, the effects are not related to the physical experience of a particular addictive substance or behavior. Instead, the effects are part of a broad spectrum of behaviors the individual engages in because he or she has a genetic predisposition toward impulsivity.

Nurture Also Plays a Part

Despite our rapidly expanding knowledge of the human genome, we can’t blame addiction entirely on heritability. In fact, it is abundantly clear that environmental factors also play a significant role. But how big a role is it, and how can we measure it? One way that scientists have separated nature and nurture in addiction causation studies is by looking at the incidence of addiction among adopted children and twins (especially identical twins who were separated at birth and raised by different sets of parents). In this way, the relative influence of genetic risk factors versus environmental risk factors can be measured. Naturally these studies do reveal genetics as a key element, but they also show that genes aren’t the only driving force.

Adoption studies typically ask: What happens to the children of alcoholics if they’re adopted into a family where neither parent abuses alcohol? In one such study, men that had biological but not adoptive parents who were alcoholics were compared to a control group of men for whom neither biological nor adoptive parents were alcoholics. The men in the first group, those with an alcoholic biological parent, were four times more likely to develop alcoholism. So we can score a point for nature over nurture – though not entirely, as being four times as likely to develop alcoholism doesn’t mean that all of those men developed alcoholism. Plus, plenty of biological children of non-alcoholics do become alcoholic. So that’s a point for nurture over nature.

Studies of twins are even more enlightening. First of all, there are two types of twins: dizygotic (fraternal) twins, who have half their genes in common, and monozygotic (identical) twins, who carry exactly the same genes. Research shows that siblings in both twin types show a common risk toward alcohol abuse. If one twin is alcoholic, there is an increased likelihood that the other is also alcoholic. Predictably, the correlation is higher for identical twins than it is for fraternal twins. That said, the numbers do not exactly match up, and there are plenty of instances where one identical twin is alcoholic and the other is not, regardless of whether they were raised together or separately. As such, the genetic predisposition toward addiction is not an automatic life sentence. Nurture plays a part.

Comparable studies have been conducted for cocaine, nicotine, and opiates with remarkably similar results, leading scientists to conclude that somewhere between 40 and 70 percent of the risk for addiction is genetic, and somewhere between 60 and 30 percent is environmental. If we wanted to use the center-point of those estimates, we could say that the risk for addiction is 55 percent genetic and 45 percent environmental. In addition to this relatively even distribution of blame, it appears that nature can be easily overridden by nurture. For instance, abused and/or neglected children are incredibly at-risk for addiction regardless of genetic influences.

The simple truth is most people who become addicts are subject to a combination of risk factors. For instance, a combination of genetic predisposition, alcoholic parents, childhood trauma, and early exposure occurs relatively often, nearly always creating a witch’s brew of ongoing life problems, including numerous emotional and psychological issues in addition to addiction. Given this, it is clear that any discussion of risk factors for addiction is not so much an argument about nature versus nurture as an examination of how the two factors come together to influence individual behavior and response. In short, addictive disorders can be driven by either genetics or environmental factors alone, but much more often they are influenced by both.