Thursday, December 27, 2012

Why Have Tobacco Control Policies Stalled? Using Genetic Moderation to Examine Policy Impacts

Research has shown that tobacco control policies have helped produce the dramatic decline in use over the decades following the 1964 surgeon general’s report. However, prevalence rates have stagnated during the past two decades in the US, even with large tobacco taxes and expansions of clean air laws. The observed differences in tobacco control policy effectiveness and why policies do not help all smokers are largely unexplained.

The aim of this study was to determine the importance of genetics in explaining response to tobacco taxation policy by testing the potential of gene-policy interaction in determining adult tobacco use.
A moderated regression analysis framework was used to test interactive effects between genotype and tobacco policy in predicting tobacco use. Cross sectional data of US adults from the National Health and Nutrition Examination Survey (NHANES) linked with genotype and geocodes were used to identify tobacco use phenotypes, state-level taxation rates, and variation in the nicotinic acetylcholine receptor (CHRNA6) genotype. Tobacco use phenotypes included current use, number of cigarettes smoked per day, and blood serum cotinine measurements.

Variation in the nicotinic acetylcholine receptor was found to moderate the influence of tobacco taxation on multiple measures of tobacco use. Individuals with the protective G/G polymorphism (51% of the sample) responded to taxation while others had no response. The estimated differences in response by genotype were C/C genotype: b = −0.016 se = 0.018; G/C genotype: b = 0.014 se = 0.017; G/G genotype: b = −0.071 se 0.029.
This study provides novel evidence of “gene-policy” interaction and suggests a genetic mechanism for the large differences in response to tobacco policies. The inability for these policies to reduce use for individuals with specific genotypes suggests alternative methods may be needed to further reduce use.
Tobacco use is among the most important causes of morbidity and the leading preventable cause of death in the US, with over 400,000 deaths per year [1]. This number accounts for more deaths than AIDS, alcohol use, cocaine use, heroin use, homicides, suicides, motor vehicle crashes, and fires combined [2], [3]. Although studies suggest that as much as 70% of the variance in nicotine dependence and other tobacco use phenotypes could be due to genetic factors [4], the principal policies to reduce tobacco use have been broad-based and non-targeted. Following economic theory, governments have sought to increase the price of tobacco in order to reduce consumption [5]. Indeed, one of the most successful policies to reduce tobacco use has been tobacco taxation [6], helping to reduce use by over 50% since the mid 1960 s, which has been suggested as one of the most successful public health interventions in the 20th century [3], [7]. Following recommendations from the IOM and other groups [3], recent large increases in tobacco taxes have been made. For example, in April 2009, the largest federal excise tax in history went into effect, bringing the average combined federal and state rates to over $2 per pack.
The state-level per-pack tobacco tax rate [was] ...on average ... nearly $0.25 and varied from $0.02 to $0.56 across states.
The full results are presented in the table below:

Results from three separate regression analyses estimating the association between state level tobacco tax rates and tobacco use based on CHRNA6 genotype (C/C, G/C, G/G). Among the 1,278 individuals with C/C genotype, the estimated tax effect was not significant (b = −0.016, SE = 0.018, z = .89, P = 0.37). Among the 2,328 individuals with the G/C genotype, the estimated tax effect was not significant (b = 0.014, SE = 0.017, z = .82, P = .41). However, among the 2,572 individuals with the G/G genotype, the estimated tax effect was statistically significant (b = −0.071, SE = 0.029, z = 2.44, P = 0.0148). These effects were statistically different based on genotype.

Unadjusted differences in tobacco tax use as predicted by the logged values of the tobacco tax indicates that a 100% increase in the tax rate is associated with a 3.1 percentage point reduction in the likelihood of reporting tobacco use.  Unadjusted differences in tobacco use as predicted by genotype shows that individuals with the G/G genotype are 3.7 percentage points less likely to report current tobacco use than individuals with C/C or C/G genotype.

by Jason M. Fletcher, E-mail:
Volume 7, Issue 12 e50576.
Editor: Balraj Mittal, Sanjay Gandhi Medical Institute, India
Received: July 25, 2012; Accepted: October 23, 2012; Published: December 5, 2012

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