Smoking is not only bad for physical health, it may also be bad for mental health, a new study suggests. Smoking cigarettes could increase the risk of developing psychiatric disorders, and may even be linked with suicide, the research shows.
In the study, researchers looked at the correlation between tobacco policies — such as taxes and public smoking bans — and rates of suicide in all 50 U.S. states between 1990 and 2004.
Results showed that states adopting aggressive tobacco-control policies saw a marked decrease in suicide rates, compared with the national average.
"Our analysis showed that each dollar increase in cigarette taxes was associated with a 10-percent decrease in suicide risk," said study researcher Richard Grucza, an epidemiologist and associate professor of psychiatry at Washington University in St. Louis. "Indoor smoking bans also were associated with risk reductions."
Researchers observed the opposite effect in states whose tobacco policies were more lax. For example, in those states with lower tobacco taxes and more-lenient policies toward smoking, the suicide rate increased by up to 6 percent over the study period. [5 Myths About Suicide, Debunked]
Since the 1970s, scientists have said that a causal relationship might exist between cigarette smoking and suicide, Grucza told Live Science. But because smoking was not always seen as a serious addiction, few studies have been conducted to test the hypothesis that more smoking leads to higher rates of suicide.
"Since that time, there's been a lot more research on the brain and on the mechanisms of nicotine addiction, as well as the other harmful compounds in smoke, like carbon monoxide," Grucza said. This research led him and his team to pursue a more rigorous test of the smoking/suicide hypothesis.
In doing so, the researchers found that smoking is related to higher rates of suicide. But as Grucza explained, it's hard to know whether there is a cause-and-effect relationship, for several reasons. For one thing, scientists cannot conduct a randomized controlled trial, because they can't force people to smoke and then see whether those individuals are more likely to become suicidal, Grucza said.
An alternative way to determine whether there is a linkis to do what the researchers did for this study: look at how smoking policies, which are known to influence smoking behaviors, relate to suicide rates.
"What we found was a clear correspondence," between people's suicide risk and cigarette taxes and smoke-related policies, Grucza said.
The researchers believe that this link between smoking and suicide may have to do with smoking's effect on a person's psychiatric health. Using cigarettes might trigger psychiatric disorders, or worsen an already-existing psychiatric disorder, the researchers said.
"There's a lot of research coming out in the neurobiological literature that suggests that smoking could cause anxiety or depression," Grucza said. "We already know that psychiatric patients tend to smoke more, so it could be a kind of a vicious cycle, where people with psychiatric disorders smoke to make themselves feel better in the short term, but in the long term, it ends up making their symptoms worse."
For now, the exact nature of the link between smoking and psychiatric health remains unclear, Grucza said. But what is clear is that more studies are needed to determine what mechanism might link smoking with an increased risk of suicide, he said.
Gruzca said that he believes the culprit could be nicotine.
"Nicotine is a plausible candidate for explaining the link between smoking and suicide risk," Grucza said. "Like any other addicting drug, people start using nicotine to feel good, but eventually they need it to feel normal. And as with other drugs, that chronic use can contribute to depression or anxiety, and that could help to explain the link to suicide."
However, Grucza said that researchers can't rule out other compounds present in cigarette smoke as the mechanism that pushes some smokers to suicide. For example, the smoke also contains carbon monoxide, which leads to decreased blood-oxygen levels over time.
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