We know smoking causes cancer and sometimes it even causes death. But this one is new: Smoking increases risk of suicide.
The idea is sketched by German researchers, who say an in-depth study among young people in Bavaria found a clear and alarming link between smoking and the desire to kill oneself.
The investigation, published in the Journal of Affective Disorders, is based on data from a detailed psychology study launched in 1995 among 3,021 people aged 14-24 who lived in Munich.
They were interviewed again four years later, when 2,548 of the volunteers responded.
Around a quarter of these individuals had never smoked.
Of the rest, 40 percent were defined as occasional smokers, 17 percent as "non-dependent" regular smokers and 19 percent as addicted smokers.
Among non-smokers, nearly 15 percent, reported having had suicidal thoughts, defined as making plans to kill himself or herself or spending two weeks or longer with the wish to die.
The rate was around 20 percent among occasional and non-dependent smokers, but among dependent smokers, suicidal ideation was 30 percent.
An even more pronounced pattern was found among the 69 individuals who had actually tried to commit suicide.
Only 0.6 percent of the non-smokers said they had sought to end their life; among non-dependent smokers, the rate was 1.6 percent; but among addicted smokers, it was a whopping 6.4 percent.
To ensure that the results were not being skewed by other factors, the researchers stripped out alcohol use, illicit drug use and a history of depression among the volunteers.
They found the result was the same: the more a person smoked, the likelier he or she would have suicidal ideation.
"Campaigns for reducing smoking should also point to the elevated risk of suicidality for occasional and regular smokers," say the authors, led by Thomas Bronisch of the Max Planck Institute of Psychiatry in Munich.
They acknowledge that there were several limitations to their study.
One was that in the four-year follow-up, no suicides actually occurred, so that the conclusions of the study are based on suicidal ideas and attempts rather than the completion of the act.
And because some of the volunteers were still in their early teens when the study was launched, they had not passed through a known risk period for suicide among young people by the time the study was over.
Previous investigations have likewise seen an association between suicide and smoking but also left unsettled the big question as to whether smoking causes the malaise or is just a symptom of it.
Some research suggests that nicotine depletes a vital pleasure-giving brain chemical called serotonin, and the risk could be higher among individuals with a genetic susceptibility to this effect.
Other studies, though, have suggested there are underlying personality characteristics such as impulsiveness, aggression and neuroticism that predispose a person to smoking and to suicide.
Meanwhile, other research has suggested that tobacco smoke may contain antidepressant compounds that may encourage depressed individuals to smoke.