Smokers with a history of psychological illness, and with evidence of impaired chemical function in the brain, are more likely than non-smokers to attempt suicide, research published today suggests.
Researchers led by Prof Kevin Malone, professor of psychiatry at UCD and consultant psychiatrist at St Vincent's Hospital, found a direct link between the number of cigarettes smoked and the seriousness of the suicide attempt.
The study identifies changes in brain chemistry which were associated with both smoking and suicidal behaviour.
The analysis of 350 patients with a psychiatric disorder, including people with schizophrenia, depression and bipolar illness, found that patients who smoked the most cigarettes were more likely to attempt suicide and to have the greatest lowering of levels of a neurotransmitter serotonin.
This chemical is central to normal brain function; modern anti-depressant drugs called selective serotonin uptake inhibitors (SSRIs) work on the principle of restoring depleted serotonin levels in the brain.
"Our findings dispel the myth that the previously noted association between smoking and suicide is purely due to the presence of psychiatric illness. The latest biological findings concerning alterations in serotonin neurotransmitter function indicate that something else is going on in the brain of these patients," Prof Malone told The Irish Times.
"I don't think it's coincidental and I don't think it's benign. I think it's just the tip of the iceberg," he added.
The research, published in the April issue of the American Journal of Psychiatry, was conducted among an equal number of men and women. Patients had no history of substance abuse or alcohol dependence, and were not taking psychiatric medication at the time of the study.
Previous studies have shown that the chronic administration of nicotine decreases the level of serotonin in the brain. Post-mortem analysis of human brain tissue has found that smokers had significantly lower concentrations of the neurotransmitter in an area called the hippocampus. In this latest study, doctors carefully measured blood and brain serotonin levels in live patients with depression.
Prof Malone carried out the research with colleagues at the Centre for Suicide Research at Columbia University, New York.