When one hears the word “addiction” the immediate thought is most likely to include “drugs”. This is only natural, as newspaper and television reports constantly refer to drug addiction in some form or another. The World Health Organisation (WHO) refers to substances like heroin where heroin centers Miami come in, as well as opium, cannabis, alcohol, amphetamines and tranquilizers when they talk about addiction, and a search on PubMed is more likely to yield results including these drugs than anything else, if only because they are the most studied means of addiction.
Certainly the WHO defines addiction as “using a substance repeatedly, despite knowing and experiencing its harmful effects”, and this is by and large true. Yet there are non-pharmaceutical addictions which can have equally harmful effects, be they social or health-related; gambling, sex and food spring to mind. It may be correct to use the term “substance-dependency” for drug use, but physical and psychological dependence are both intrinsically linked to each other and share the same biochemical patterns.
Dopamine and Addiction – What Makes Us Addicted?
There is evidence emerging that all types of addiction lead to the same changes in the brain. Certainly chemical dependence causes rewiring of the brain’s dopamine and serotonin pathways (Siegel A and Sapru HN, Essential Neuroscience, pub. Lippincott Williams and Wilkins, 517-520), simply because the substances taken artificially alter dopamine levels. Yet gambling has been shown to do the same, as has food. Essentially, anything that causes a “feel-good” response will cause dopamine and serotonin to be released.
So addiction ought to be defined as any substance or behaviour which leads to a dependence on dopaminergic alterations in the central nervous system; this would cover all bases with regard to drugs, food, gambling and so on. Even the mere thought of the substance or behaviour is usually enough to elicit cravings and a response; one study by Heinz et al showed that certain cues could elicit a neuronal response in alcoholics.
Heinz’s study used magnetic resonance imaging (MRI) and positron emission tomography (PET) to show changes in the dopamine pathways: recovering alcoholics have fewer dopamine type 2 receptors (D2) than healthy subjects and this is closely linked to a high relapse rate. Similar changes have been shown by other groups using PET and MRI in other forms of dependence, such as food and gambling (see previous links).
Psychological Dependence and Dopamine – the Same as Physical Dependence?
What causes this change is the release of a protein known as cocaine-amphetamine-related-transcript (CART), so called because cocaine and amphetamine were the first stimulants to be implicated in its production. Busto et al have linked CART release in the hypothalamus (the region of the brain commonly linked to reward behaviour) to several drug-seeking changes in the brain, especially that of dopamine stimulation. The authors note that some genetic alterations to CART may predispose individuals to addiction.
The best treatment by far is detoxification and abstinance (sometimes with the aid of less-addictive substances), but as yet no study has shown any kind of reversal of the brain signalling pathways. In other words, an addict remains an addict for life. A sufferer has to abstain from the substances or behaviours that led to their addiction or risk relapse.
This makes food addiction all the more tragic: while it might be possible for someone to never drink another drop of alcohol or smoke another cigarette in their entire life, try telling someone who was morbidly obese to never eat again. Even with diet and exercise (and a great deal of hard work) a person who loses weight can find it all too easy to relapse and begin overeating – after all, food is readily available in the western world and we need it to survive. But the temptation will be there, and in all likelihood stronger than that for alcohol, say, or tobacco.
It is all too easy for people to pour scorn upon any addict – whether they are substance abusers, alcoholics, obese – but were it not for circumstance the roles could be so easily reversed. That addict could be anyone. It could even be you.