Strong Link to Suicide Found for Anxiety, Conduct Disorders

In developed countries, 52 percent of adults who had at least suicidal ideation reported a prior psychiatric disorder, compared with 43 percent in developing countries. Among those who made suicide attempts, the prevalences of prior psychiatric disorder were 66 percent and 55 percent, respectively.

One of the surprising findings was that, although it has been widely cited that over 90 percent of people who committed suicide have psychiatric disorders, the rates of psychiatric disorders reported by people in this study with suicidal ideation and attempts were lower than that, said the study's lead author Matthew Nock, Ph.D., professor of the social sciences in the Department of Psychology at Harvard University.

In an interview with Psychiatric News, Nock noted that the apparent inconsistency between previous and current data may be explained by several factors. First, it is difficult to make a postmortem psychiatric diagnosis for people who have died of suicide, and thus previous studies may have overestimated the presence of psychiatric disorders. Second, people who“ succeed” in suicide may have a higher rate of psychiatric disorders than those who have made nonfatal attempts or have suicidal thoughts. It is also possible that, beyond psychiatric disorders, “there are other factors that contribute to suicide attempts,” said Nock.

Analyzed separately, each psychiatric disorder, as identified by the survey, was associated with an increased risk of a subsequent suicide ideation or attempt compared with having no psychiatric disorders, the study authors found. Most of the associations remained statistically significant in both developed and developing countries after controlling for potentially confounding factors.

The magnitude of associations varied by the type of disorder and country type, the study revealed. Mood disorders, including bipolar disorder, depression, and posttraumatic stress disorder (PTSD), were the strongest predictors of suicide attempts in developed countries. However, PTSD, substance use disorders, and conduct disorder were the strongest predictors in developing countries.

Perhaps because past research tended to concentrate in developed countries, the importance of a history of conduct disorder is greatly underappreciated and underresearched, Nock observed. “Clinicians and policy makers should pay more attention to people with a history of conduct disorder in prevention efforts,” he said.

Another important predictor for suicidal attempts was the number of comorbid psychiatric disorders, the study found. For example, in developing countries, having one disorder was associated with a risk ratio of 3.9 for suicide attempt compared with having no disorder, while having three disorders was associated with a risk ratio of 14.2.

Despite more research efforts and public health attention on suicide prevention, the incidence of suicide has declined much in the past two decades, the researchers noted. “Because the population base rate for suicide attempts is low, it is very difficult to study and requires a very large sample,” said Nock. The size of this worldwide survey, therefore, was particularly valuable for conducting sophisticated analyses to help understand the causes of suicide.

“One of the most unexpected findings was that, although depression was among the strongest predictors of suicidal thoughts, it was not at all a strong predictor of who is likely to progress from thoughts to attempts,” commented Nock. The study also found no association between major depression and impulsive suicidal attempts.

Instead, the study found that PTSD, bipolar disorder, conduct disorder, and substance use disorders were the strongest predictors of individuals with ideation who were at higher risk of making suicide plans and attempts.“ Only disorders characterized by anxiety and poor impulse control predict which people with suicide ideation act on such thought,” they concluded in the report.

With new insights, Nock admitted, the study poses a number of questions, including “Are there different mechanisms for suicidal thoughts and suicide attempts?” He and his colleagues plan to conduct additional analyses on the data to better understand the risk and protective factors associated with suicidal behaviors, including lifespan risks and symptom clusters.

“We plan to drill down to what types of symptoms are more predictive of suicidal behaviors, because many psychiatric disorders are quite heterogeneous,” said Nock.

“Cross-National Analysis of the Associations Among Mental Disorders and Suicidal Behavior: Findings From the WHO World Mental Health Surveys” is posted at<www.plosmedicine.org/article/info:doi%2F10.1371%2Fjournal.pmed.1000123>.▪