Smoking twins show why it’s hard to quit

U. COLORADO-BOULDER (US) — Smokers today are influenced by genetic factors far more than social ones—which can make it even harder to quit, according to a new study with twins.

The findings show that adult identical twins sharing a common genetic structure are significantly more likely to quit smoking at the same time compared with fraternal twins who do not share identical genes.

The genetic influence has increased in importance among smokers since the initial restrictive legislation on smoking enacted in the United States in the 1970s, says Fred Pampel, professor of sociology at the University of Colorado-Boulder and co-author of the study.


“In the past, when smoking rates were higher, people smoked for a variety of reasons,” adds Pampel. “Today the composition of the smoking population has changed.  Smokers are more likely to be hard-core users who are most strongly influenced by genetic factors.

“These days people don’t smoke as much for social reasons,” Pampel says. “They in fact face criticism for the habit but tend to smoke because of their dependence on nicotine.”

Using a database of twins who responded to an extensive health questionnaire, researchers examined the smoking patterns of 596 pairs of twins, 363 of them identical and 233 of them fraternal. The researchers looked at their smoking patterns from 1960 to 1980 because they wanted to focus on a period of changing views about smoking.

Among identical twins, 65 percent of both twins quit during a two-year timeframe if one twin quit, but among fraternal twins, the percentage dropped to 55 percent, a statistically significant difference that indicates a genetic component at work.

While a specific genetic marker has been hard to identify among those who smoke, certain genetic similarities can be inferred.  “If one identical twin quits the other is likely to quit,” Pampel says. “And if one twin continues so is the other twin.”

The study, published in the journal Demography, has implications for current public policies aimed at reducing smoking, which may be becoming less effective. Since the early and mid 1970s when restrictive anti-smoking legislation began to be enacted in the United States, many smokers have quit. “Prior to 1975 this (potentially genetic) pattern wasn’t clear because there were so many smokers.”

Two of today’s main anti-smoking policies include heavy taxes on cigarettes and vast reductions in the number of public spaces where smoking is allowed, particularly in bars and restaurants.

But with indications that the genetic component is growing, it may be time to treat smoking more like an addiction than a choice, Pampel says, including placing more emphasis on nicotine-replacement therapy and counseling.

Researchers from Penn State and Washington University in St. Louis were co-authors on the paper.

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