All around, the SLC6A3-9 population seems less susceptible to the lure of cigarettes. A related investigation, headed by Dean Hamer of the National Cancer Institute, revealed that only 20 percent of smokers who try to kick the habit actually succeed. Looking further, Hamer and his group examined 1,107 nonsmokers, current smokers, and former smokers. Within this population, the researchers discovered that the SLC6A3-9 gene is associated with personality traits that influence a person's ability to start or stop smoking. His team also found that individuals who possess the SLC6A3-9 variant were one and a half times more likely to have quit smoking than those without the gene.
Genes also influence the attraction to caffeine, at least among women.
The researchers reached their conclusions after interviewing 1,934 female twins about their consumption of brewed and instant coffee, tea, and caffeinated soft drinks. Identical twin pairs, unlike fraternal twins, showed almost the exact same total caffeine consumption, intoxication, tolerance, and withdrawal. From a genetic perspective, addiction to caffeine looks much like that of other drugs of abuse, according to Kendler. In both cases, genes have a significant effect on the likelihood of getting hooked. So there are a lot of addicts out there.