Low IQ Linked to Suicide Risk

But diminished intellect may be mask for undiagnosed mental illness, study says

THURSDAY, Jan. 20, 2005 (HealthDayNews) -- A low IQ may be a risk factor for suicide.

A new study has found that young men with the lowest intellectual capacity are up to three times more likely to take their own life, compared with those with the highest test scores.

Experts' understanding of the causes of suicide is growing, said lead researcher Dr. David Gunnell, a professor of epidemiology at the University of Bristol in England. "This finding is a pointer to a factor associated with risk that requires elucidation. Right now, the practical implications are not clear-cut," he added.

In their study, Gunnell and his team collected data on 987,308 young Swedish men, who were about to enter the military. The researchers followed the men for up to 26 years. During that follow-up, there were 2,811 suicides.

"We looked at the association between scores of intelligence tests and later suicides," Gunnell said. "There was about a two- to three-fold difference among those scoring best on the test and those scoring least well, with the higher risk being those at the lower end of the scale."

The findings appear in the Jan. 22 issue of the British Medical Journal.

Gunnell speculated that because poor performance on IQ tests has been associated with greater risk of mental illness, particularly schizophrenia, that could explain the finding. People who suffer from schizophrenia are at a considerably higher risk for suicide than the general population, he added.

Another reason for the association may be that people who perform poorly on IQ tests make poorer life choices. "They are more likely to occupy lower-income jobs," Gunnell said. "And because of the association of poverty with suicide, that may contribute with the association."

Furthermore, those who score higher may have a better ability to cope with depression and other life problems. "It could simply be that what we are seeing here is the difference between individuals and their capacity to problem-solve when faced with severe life events," Gunnell said.

Whether the link between IQ and suicide is the same for women remains an open question. But Gunnell suspects the same association might hold true, given the connection between lower IQ and mental illness in women, he noted.

While this is an observational study with limited practical application, Gunnell believes the finding may be useful in the future. "These findings raise questions, the answers to which may be important in our understanding the causes of suicide and being able to use that understanding to prevent these deaths," he said.

M. David Rudd is chairman of psychology and neuroscience at Baylor University, and president of the American Association of Suicidology. "Suicide is most often the function of a constellation of factors, not any single one, like poor performance on an IQ test," he said. "There's no real way to know whether the low IQ scores were a function of a preexisting mental illness."

The overwhelming majority of people who commit suicide suffer from a mental illness. So the new study findings should be considered, Rudd said. "Mental illness tends to result in a broad range of cognitive symptoms and disruption, any of which would lower performance on an IQ test," he noted.

Rudd added that many variables may be at play when it comes to suicide, including coexisting medical disorders, poor problem-solving, substance abuse, and issues such as social support among family and friends. "In suicide research, one thing that is often true is that associations such as this are usually not isolated," he said.

"What we know for certain among suicide cases is that the real culprit tends to be undiagnosed, untreated or undertreated mental illness," Rudd said.

More than 30,000 people commit suicide in the United States each year, according to the U.S. Centers for Disease Control and Prevention.

More information

The National Institute of Mental Health has more about suicide.

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