Banning smoking in the workplace and increasing taxes on cigarettes have discouraged teens and young adults from taking up smoking, according to a study by researchers at UC San Francisco and UC Merced.

The study, published today (Sept. 8, 2015) in JAMA Pediatrics, used data on the smoking habits of a group of 12- to 18-year-olds living throughout the country in 1997. They were tracked for 11 years as they transitioned to young adults.

The researchers found that a 100 percent smoke-free environment reduced the odds of taking up smoking by one third and that the number of new smokers plummeted over time. These effects impacted nonsmokers by protecting them from the toxins of secondhand smoke.

The researchers, led by Stanton Glantz, PhD, UCSF professor of medicine, used data from the Bureau of Labor Statistics' National Longitudinal Survey of Youth 1997, which was established to study health, education, attitudes and lifestyle habits of close to 4,000 respondents, representative of the U.S. population.

During the period studied, smoke-free laws on the state, county and city level were becoming more commonplace and comprehensive, and cigarette taxes had increased.

In 1997, no respondent had a 100 percent probability of being covered by a 100 percent smoke-free workplace law, 11.6 percent had a 100 percent probability of being covered by a smoke-free restaurant law and 11.6 percent had a 100 percent probability of being covered by a smoke-free bar law. But by 2007, these numbers had risen to 27.3 percent, 43.3 percent and 36 percent respectively.

The researchers found that adolescents and young adults living in areas with 100 percent smoke-free bar laws were 20 percent less likely to be smokers, and that current smokers smoked 15 percent fewer days per month than those not living under these laws.

"Smoke-free workplace laws have the most powerful effect on smoking initiation, equivalent to the deterrent impact of a $1.57 tax increase," said Glantz, the study's senior author.

According to the Centers for Disease Control and Prevention, federal tax had jumped from 24c per pack in 1995, two years before the study period, to $1.01 per pack in 2009, two years after the study period. The average state taxes for 1995 and 2009 had increased from 32.7c to $1.20 per pack.

The authors found that these tax hikes had an impact beyond the effects of smoke-free workplace laws, with each 10c tax increase followed by a 3 percent drop in the odds of starting to smoke. "Our results suggest that the $2 tax increase being discussed in the California legislature would cut youth smoking initiation nearly in half," said Glantz.

"Because smoking initiation typically occurs before youth enter the workplace, smoke-free workplace laws likely affect smoking initiation by showing kids that adult smoking norms reject smoking," said first author Anna Song, PhD, of the UC Merced Health Sciences Research Institute. "The effects of smoke-free laws are similar or larger than other determinants of smoking, including age, sex, race/ethnicity and poverty level."