Previous research has shown that smokers are more likely to commit suicide than people who do not smoke. The factor driving this association was assumed by some researchers to be because people with psychiatric disorders are both more likely to smoke and more likely to commit suicide than the general population.
The map displays the range of state cigarette taxes from the lowest (lightest blue) to the highest (darkest blue).
Image credit: Richard A. Grucza, PhD
However, the new study suggests that it may be smoking itself that increases suicide risk - possibly increasing the risk for psychiatric disorders, or making existing disorders more severe. The study also claims that policies aimed at limiting smoking may reduce suicide rates.
"We really need to look more closely at the effects of smoking and nicotine, not only on physical health but on mental health, too," says lead author and associate professor of psychiatry Richard A. Grucza, PhD.
"We don't know exactly how smoking influences suicide risk. It could be that it 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."
The Washington University team analyzed National Center for Health Statistics' data from 1990 to 2004, a period when individual states began to take different approaches to cigarette taxes and smoking policies.
Fast facts on US suicide rates
- The average annual suicide rate during the study period was about 14 deaths for every 100,000 people
- Suicide is the 10th leading cause of death in the US, according to the Centers for Disease Control and Prevention
- In 2010, nearly 40,000 people died of suicide across the US.
The National Center for Health Statistics records data on every death that occurs in the US. The researchers looked at the states where each person who had committed suicide had lived, and how aggressive the tobacco policies in those states were.
They found that in the states that adopted aggressive tobacco-control policies, suicide rates decreased compared with the national average.
By contrast, in states with low cigarette taxes and less restrictive smoking policies, suicide rates were shown to be up to 6% higher than the national average during the same period.
The researchers also determined whether the people who had committed suicide were likely to have been smokers. They claim that suicide risk among the people most likely to smoke was associated with smoking restrictions and tobacco taxes.
"Our analysis showed that each dollar increase in cigarette taxes was associated with a 10% decrease in suicide risk," Grucza says. "Indoor smoking bans also were associated with risk reductions."
Nicotine may be an important influence on suicide risk, says Dr. Grucza:
"Nicotine is a plausible candidate for explaining the link between smoking and suicide risk. 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."
Grucza adds that he is concerned that many restrictions on public smoking do not cover e-cigarettes, which deliver nicotine through a vapor rather than smoke. He also hypothesizes that if states that have low cigarette taxes and relaxed smoking policies raise taxes and restrict public smoking, then their suicide rates will most likely fall.