Restrictive Policies Push Gene Influence on Smoking Behavior

Monozygotic twins more likely to quit smoking within a similar time frame than dizygotic twins

MONDAY, Nov. 21 (HealthDay News) -- Compared to dizygotic twins, monozygotic twins are more likely to quit smoking during a similar time frame, and the influence of genetic factors was more pronounced in 1975 to 1980 than in 1960 to 1974, coincident with the implententation of restrictive smoking legislation, according to a study published in the November issue of Demography.

Jason D. Boardman, Ph.D., from the University of Colorado in Boulder, and colleagues described the similarity in the timing of smoking desistance among adult twin pairs. Data were collected for 596 pairs of twins, including 363 monozygotic pairs and 233 same-sex dizygotic pairs, in which both members of the pair reported having smoked daily at some point in their lives. The sample was restricted to pairs in which the first to quit did so between 1960 and 1980. Cox proportional hazard models were used to investigate the association by period of desistance.

The investigators found that 65 percent of monozygotic twins quit smoking following desistence of their twin during a two-year time frame, while the measure was significantly lower, at 55 percent, among dizygotic twins. Monozygotic twin pairs quit, on average, within 10 years of each other, and dizygotic twins within 11 years (P < 0.49). The average difference in the time of quitting among pairs in which both twins quit was 8.5 years for dizygotic twins and 7.5 years for monozygotic twins (P < 0.12). Modeling indicated that there was little evidence for genetic influences for time periods from 1960 to 1974, but the influence was notably higher for 1975 to 1980.

"The policy changes thus coincided with increases in the extent to which genetic risk characterizes the population of smokers," the authors write.

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