Since 2009, total deaths from suicide in the U.S. surpassed deaths from motor vehicle crashes, while the number of middle-aged Americans taking their lives has risen as well. Such statistics set off alarm bells among public health officials seeking to learn more about those who self-destruct. While past studies have shown cigarette smokers to be more likely to commit suicide than people who don’t smoke, a new study from Washington University School of Medicine has arrived at a more nuanced view of the issue. Smoking itself may increase suicide risk, researchers say, and whenever policies to limit smoking have been enacted, suicide rates have declined.

“States started raising their cigarette taxes… [and] higher taxes and more restrictive smoking policies are well-known ways of getting people to smoke less,” explained Dr. Richard A. Grucza, assistant professor, Department of Psychiatry. “So it set a natural experiment, which shows that the states with more aggressive policies also had lower rates of smoking. The next thing we wanted to learn was whether those states experienced any changes in suicide rates.”

To begin his experiment, Grucza followed the data. Every death that occurs in the U.S. is recorded in a database managed by the National Center for Health Statistics. Using this database, Grucza and his research team identified suicides and determined whether the deceased may have smoked. Next, the research team pinpointed the state where the suicide took place and how aggressive that state’s tobacco policies were. Using statistical analysis, the researchers compared rates of suicide in states with stricter tobacco policies to rates in states with more lenient laws and lower taxes.

“Our analysis showed that each dollar increase in cigarette taxes was associated with a 10 percent decrease in suicide risk,” Grucza said. “Indoor smoking bans also were associated with risk reductions.”

From 1990 to 2004, the average annual suicide rate was about 14 deaths for every 100,000 people. During that period, states which had adopted aggressive tobacco-control policies saw their suicide rates decrease, compared with the national average. Completing the dataset, the team also found the opposite to be true in states with lower cigarette taxes and more lax policies toward smoking in public. In those states, suicide rates increased up to six percent, relative to the national average, during the same time period.

“We really need to look more closely at the effects of smoking and nicotine, not only on physical health but on mental health, too,” Grucza said. “It could be that [smoking] affects depression or increases addiction to other substances. We don’t know how smoking exerts these effects, but the numbers show it clearly does something.”

He explained that many states still have low cigarette taxes, while other states haven’t adopted comprehensive smoke-free air policies. Grucza predicts that if these states raise their cigarette taxes and restrict smoking in public, their suicide rates likely would fall. He is also concerned many new restrictions on public smoking don’t cover e-cigarettes. “Nicotine is a plausible candidate for explaining the link between smoking and suicide risk,” Grucza said. “As with other drugs … chronic use can contribute to depression or anxiety, and that could help to explain the link to suicide.”

Source: Grucza RA, Plunk AD, Krauss MJ, et al. Proving the smoking-suicide association: Do smoking policy interventions affect suicide risk? Nicotine & Tobacco Research. 2014.