The heated discussion that followed the story on cigarette package warning labels hit on a number of interesting themes. Various people noted the differences between noticing the warnings and having their message register, while others questioned their effectiveness in the face of an addiction. A few people brazenly claimed that warning messages lead them to want to smoke more. In a bit of luck, a set of papers have come out recently that roots a lot of these issues in biology itself, so I'll do a quick rundown on the data.
Human Molecular Genetics has published three articles that explore the genetics of nicotine addiction in humans within the past month. It turns out that families have been recruited into several study populations that include DNA samples and track factors related to smoking.
One of these studies built on prior data that had identified an area on chromosome 17 as being potentially involved in nicotine addiction. As it turned out careful analysis found not one, but two genes within this region that predisposed individuals to nicotine addiction. Both of these have been found to associate with receptors for neural signaling molecules in the past (GABA and NMDA receptors, specifically). A second study took a broader look at the genome by looking for association between addiction and 300 different genes, most involved in the function of the nervous system. Several genes stood out, including an ion channel (used in transmitting electrical impulses down nerves) and a gene that acts as a general modulator of nerve activity. But the strongest linkage was to a single base change in a nicotinic receptor. When people had two copies of this change, they were over two-fold more likely to get hooked on nicotine.
The final study was about as broad as you can get; the researchers involved scanned the entire genome of nearly 2,000 individuals using about 32,000 individual DNA markers. Some of the same genes came up in this study, but many of the strongest linkages were to genes involved more generally in establishing contacts between nerve cells and their targets. This suggests that simply pursuing such studies based on our expectations may cause researchers to miss out on important factors. Overall, the research also suggests that nicotine addiction may be a broad problem that encompasses a variety of distinct genetic predispositions, each of which may be more or less amenable to certain types of treatment.
The last study I want to mention is pure psychology, but it gets at why some smokers engage in self-destructive behavior in part because it annoys others. The researchers surveyed study participants to identify individuals who expected the participant to have fun, or to get a lot of work done. While performing anagram tests on a computer screen, they were subliminally exposed to one or the other of the person's names. Those who were exposed to the names of people associated with work pressure scored significantly lower than their fellows. This correlation held up in two different tests, and experimentally supports a conclusion that most of us would already assume: pressure can cause people to do the opposite of what we'd like to see them do.
So, bringing this back to to the issue at hand, this suggest that those designing the warnings have to tread a fine line between making sure that the dangers of the cigarettes are made clear and coming across as a nagging scold. For those that decide to quit smoking, the genetic studies provide the hope that treatments may eventually target the biology behind their nicotine cravings.