Alcoholism and smoking have a high rate of co-occurrence in the general population. Yet little is known about the co-morbidity of alcoholism and smoking among American Indians.
In the March issue of Alcoholism: Clinical & Experimental Research, researchers examine patterns of alcohol and tobacco use among Plains American Indians, as well as the influence that a catechol-O-methyltransferase (COMT) functional polymorphism called Val158Met may have on these behaviors.
"The shared heritability between smoking and alcoholism, particularly in heavy smokers and heavy drinkers, indicates that some genes predispose individuals to both smoking and drinking," said Mary-Anne Enoch, a staff scientist in the Laboratory of Neurogenetics at the National Institute on Alcohol Abuse and Alcoholism and corresponding author for the study. "Nicotine's effects on the brain occur mainly through nicotinic acetylcholine receptors, and alcohol acts on these same receptors to release dopamine, the 'pleasure' hormone in the brain's reward pathway."
Enoch added that the enzyme COMT plays an important role in the breakdown of dopamine and norepinephrine in the brain, its activity varying according to a common COMT polymorphism, Val158Met. "The Met allele results in a less efficient enzyme and therefore probably more dopamine and norepinephrine in the brain," she said. "The Met allele has also been associated with increased anxiety and neuroticism, increased emotionality in response to pain, and greater brain activation in response to unpleasant visual images."
Whereas studies of European men have shown that the Met allele is associated with late onset alcoholism and increased alcohol intake in social drinkers, Enoch and her colleagues have found that in American Indians the Met allele was protective against alcoholism, and the Val allele was the risk allele.
"The answer to this paradox may lie in the relationship between anxiety and drinking patterns," she said. "In societies where regular, daily drinking is the norm, such as in Europe, anxious Met individuals may be more vulnerable to alcoholism through using alcohol as a coping mechanism. In societies where heavy, periodic drinking bouts are the norm, such as in some American Indian tribes, anxious Met individuals may be less likely to participate in this kind of risky behavior and may be protected from alcoholism."
Enoch and her colleagues also found that the Val allele was a risk factor for smoking, but only in women.
For the current study, researchers recruited 342 (201 women, 141 men) community-based Plains American Indians, establishing their lifetime drinking and smoking histories. Additionally, five COMT loci - including Val158Met - were genotyped.