Humans have designed a perfect environment for addiction.
Why would anyone continue to use recreational drugs despite the medical consequences and social condemnation? What makes someone eat more and more in the face of poor health?
One answer is that modern humans have designed the perfect environment to create both of these addictions.
No one will be shocked to learn that stress makes people more likely to search for solace in drugs or food (it's called "comfort food" for a reason). Yet, the myth has persisted that addiction is either a moral failure or a hard-wired behaviour - that addicts are either completely in command or literally out of their minds. Now we have a body of research that makes the connection between stress and addiction definitive. More surprising, it shows that we can change the path to addiction by changing our environment.
Neuroscientists have found that food and recreational drugs have a common target in the "reward circuit" of the brain, and that the brains of humans and other animals who are stressed undergo biological changes that can make them more susceptible to addiction.
Consider the opioid epidemic. Last month, the New York Times estimated that more than 59,000 Americans had died of drug overdoses in 2016, which represents the largest year-over-year increase ever recorded. The Princeton economists, Anne Case and Angus Deaton, reported in a 2015 study that middle-class whites in particular have experienced an alarming increase in midlife mortality since the 1990s, driven largely by "deaths of despair" involving suicide, alcohol and drugs. These addicts did not suddenly lose their moral fibre. Instead, they faced poor job prospects, a steady erosion in their social status and, consequently, mounting stress.
In a 2010 study, Diana Martinez and colleagues at Columbia scanned the brains of a group of healthy controls and found that lower social status and a lower degree of perceived social support - both presumed to be proxies for stress - were correlated with fewer dopamine receptors, called D2s, in the brain's reward circuit. All rewards - sex, food, money and drugs - cause a release of dopamine, which conveys a sense of pleasure and tells the brain something like: "This is an important experience. Don't forget it!" The reward circuit evolved to help us survive by driving us to locate food or sex in our environment. Today, the more D2 receptors you have, the higher your natural level of stimulation and pleasure - and the less likely you are to seek out recreational drugs or comfort food to compensate.
Dr Nora Volkow, the director of the National Institute on Drug Abuse, and colleagues demonstrated this in a study of Ritalin. Healthy, non-drug-abusing subjects with fewer D2 receptors experienced the stimulant drug as pleasurable, while those with more found it aversive.
The number of receptors don't just predict drug usage; they are also affected by it. In that same study, Volkow discovered that people addicted to cocaine, heroin, alcohol and methamphetamines experience a significant reduction in their D2 receptor levels that persists long after drug use has stopped. These people are far less sensitive to rewards, are less motivated and may find the world dull, once again making them prone to seek a chemical means to enhance their everyday life.
Drug exposure also contributes to a loss of self-control. Volkow found that low D2 was linked with lower activity in the prefrontal cortex, which would impair one's ability to think critically and exercise restraint.
The same neuroscience helps us understand compulsive overeating. Food, like drugs, stimulates the brain's reward circuit. Chronic exposure to high-fat and sugary foods is similarly linked with lower D2 levels, and people with lower D2 levels are also more likely to crave such foods. It's a vicious cycle in which more exposure begets more craving.
Volkow and colleagues showed that morbidly obese individuals had reductions in their D2 receptors and that the reduction was proportional to their body mass index.
At this point you may be wondering: What controls the reward circuit in the first place? Some of it is genetic. We know that certain gene variations elevate the risk of addiction to various drugs. But studies of monkeys suggest that our environment can trump genetics and rewire the brain. The good news is that while we can't change our genetics, we can change our environment.
Michael Nader at the Wake Forest School of Medicine showed this in a study of monkeys and cocaine. When monkeys are moved from an individual cage and housed in a group, some become dominant and others assume a submissive role. The same appears true for humans. Even people who are not hard-wired for addiction can be made dependent on drugs if they are stressed. Is it any wonder, then, that the economically frightening situation that so many Americans experience could make them into addicts? You will literally have a different brain depending on your ZIP code, social circumstances and stress level.
The last important component of addiction is access. No matter how stressed you are, you obviously won't become a drug addict unless you're exposed to drugs. The same goes for compulsive overeating. Humans have been consuming food for rather a long time without the modern affliction of widespread obesity. In 1990, no state in America had an adult obesity rate above 15 per cent. By 2015, 44 states had obesity rates of 25 per cent or higher. What changed?
Contemporary humans did not experience a sudden collapse in self-control. What happened is that cheap, calorie-dense foods that are highly rewarding to your brain are now ubiquitous. Once you've had a glass of orange juice, you are not likely to be as satisfied with a healthier and less caloric orange that you have to peel.
For most of history, food was scarce, so there was a great survival advantage in scarfing down as many calories as you could when they were available. There was no flourless chocolate cake on the savanna.
Nothing in our evolution has prepared us for the double whammy of caloric modern food and potent recreational drugs. Their power to activate our reward circuit, rewire our brain and nudge us in the direction of compulsive consumption is unprecedented.
The processed food industry has transformed our food into a quasi-drug, while the drug industry has synthesised ever more powerful drugs that have been diverted for recreational use. We extracted opium from the poppy and quickly discovered how to make opiates that are a thousandfold more potent and addicting. Not content with just smoking cannabis, we bred super-potent strains of the plant, extracted the active cannabinoids and moved on to dangerous synthetic versions. The list goes on.
Finally, the advertising industry may play a role. Volkow says that she and her colleagues are now "testing how the brain responds to subliminal messages" about food and drugs. Her hypothesis is that drug-addicted and obese individuals are more susceptible to such messages.
Fortunately, our brains are remarkably plastic and sensitive to experience. Although it's far easier said than done, just limiting exposure to high-calorie foods and recreational drugs would naturally reset our brains to find pleasure in healthier foods and life without drugs.
In the meantime it's worth remembering that we can't control our genes or the misfortunes that befall us, much less their impact on our brains. Even the most self-disciplined can fall prey to a food or drug addiction under the right mix of adversity and stress.
- New York Times News Service
Richard A. Friedman is a professor of Clinical Psychiatry and the director of the psychopharmacology clinic at the Weill Cornell Medical College, and a contributing opinion writer.
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