A lower intelligence quotient (IQ) increases the risk of attempted suicide, according to British and Australian researchers.
A study following 1.1 million young people in Sweden and published in the British Medical Journal showed that people who are more intelligent attempt fewer suicides.
These results were collected over 24 years in medical testing done on young men before their military service. This was then compared with data on suicide attempts from hospital admission records.
Men with low IQs are nine times more likely to attempt suicide than those with higher intelligence.
Dr David Batty, a Wellcome Trust Fellow at the Medical Research Council Social and Public Health Sciences Unit, who led the study, says: "We have found a clear link between IQ and attempted suicide in this group of men. In common with some previous, smaller studies, we have shown that men with lower scores have a markedly greater risk of attempted suicide than men of higher IQ."
Women did not participate in this research and it did not take into account people with psychosis such as schizophrenia or severe manic depression.