Because there can never be enough research to illustrate the positive impact of public health policy on people’s health, here’s another one. This one found that comprehensive smoke-free indoor air laws resulted in a lower risk of asthma symptoms and fewer asthma-related doctor’s visits.

Based on 2007–2011 data from the Behavioral Risk Factor Surveillance System, researchers set out to evaluate whether comprehensive statewide indoor smoking bans are effective in reducing secondhand smoke exposure among nonsmoking U.S. adults. (Comprehensive smoking bans are defined as eliminating smoking in three locations: workplaces, restaurants and bars.) They compared data from Iowa, Illinois and Maryland (referred to as the experimental group), which had enacted comprehensive bans in 2008, against data from Texas and West Virginia (the control group), which did not have statewide smoking restrictions, designated smoking areas or separate ventilation laws. The study was published in the August issue of the American Journal of Public Health.

The researchers noted that while similar studies have focused on smoking bans and their effects on a specific population, such as children, this is one of the first to examine the effects of a comprehensive smoking ban on secondhand smoke exposure and asthma exacerbation among a representative sample of nonsmoking U.S. adults. Study authors Hsien-Chang Lin, Ji-Yeun Park and Dong-Chul Seo write:

The literature indicates that smoke-free indoor air laws are an effective strategy in reducing (secondhand smoke) exposure. Implementing smoke-free laws was significantly associated with a reduction in (secondhand smoke) exposure for both hospitality workers in New York and bartenders in Wisconsin. A cross-sectional analysis of the 1999–2002 National Health and Nutrition Examination Survey data demonstrated that those living in counties with extensive smoke-free air law coverage were less exposed to (secondhand smoke) than were those residing in counties without a smoke-free air law. To date, however, no study has investigated whether state-level enactment of such smoke-free air laws has reduced (secondhand smoke) exposure across multiple states at a population level in the long term.

The AJPH study found that after the implementation of indoor smoking bans, nonsmoking adults in the experimental group experienced decreased odds of reporting asthma symptoms. In addition, nonsmoking adults in smoke-free states also reported fewer asthma-related doctor’s visits. Overall, researchers found a “significant reduction” in the amount of secondhand smoke exposure after states enacted indoor smoking bans. They added that the findings boost the case for statewide smoking laws, especially since previous research has found that designated smoking rooms and specialized ventilation systems don’t work to protect people from secondhand tobacco smoke.

While the researchers noted that the study has its limitations — it’s based on just five years of data and self-reported health information — it still speaks to the success of public policies aimed at reducing the toll of tobacco. In 2014, only about half the states and Washington, D.C., had enacted a statewide indoor smoking ban that applied to worksites, bars and restaurants.

“In view of the large number of people who are still exposed to (secondhand smoke), implementing an effective regulatory policy to eliminate (secondhand smoke) exposure is warranted,” the study stated.

According to the Centers for Disease Control and Prevention, asthma costs the U.S. $56 billion every year in medical care and lost productivity. While scientists aren’t sure what causes asthma and there’s no cure, they do know that tobacco smoke exacerbates asthma symptoms and can trigger a respiratory attack. One in every 12 Americans is living with asthma.

To request a full copy of the new American Journal of Public Health study, click here.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.