A large scale study of over 1.1 million men living in Sweden that spanned nearly a quarter of a century found a link between lower IQ measured in early adulthood and higher risk of attempted suicide later in life.
The prospective cohort study was the work of Dr Finn Rasmussen, a professor in the Department of Public Health Sciences at Karolinska Institute, Stockholm, Sweden, and colleagues from the UK and Australia. They wrote a paper about it published in the 3 June online issue of the British Medical Journal, BMJ.
As well as exploring the links between early IQ scores and attempted suicide, Rasmussen and colleagues wanted to see if psychosis made a difference and also how variations in early IQ might relate to methods of attempted suicide.
Described as the largest study of its kind, they examined the medical records of nearly 1,109,500 men aged between 16 and 57 years living in Sweden.
Of these Rasmussen and colleagues found that nearly 18,000 (1.6 per cent) had been admitted to hospital at least once for attempting suicide during 24 years of follow up (after having IQ tested).
They found that men with the lowest early adulthood IQ scores were almost nine times more likely to attempt suicide then those with the highest, and there was a stepwise increase in risk across the full IQ range, which was “evident for attempted suicide by any means and for seven specific methods”.
The authors wrote that while adjustment for “childhood and adult socioeconomic status and, to a greater extent, education led to a reduction in magnitude”, the links remained strong.
However, for men who had been diagnosed with psychosis before attempting suicide, a separate analysis showed there was no such link between IQ level and attempted suicide risk.
They concluded that “low IQ scores in early adulthood were associated with a subsequently increased risk of attempted suicide in men free from psychosis,” and recommended looking more closely at the underlying mechanisms to see if they reveal opportunities to intervene and reduce rates of suicide among men.
Speculating on the reasons behind the link, they suggested perhaps because people with lower IQ tend to have lower socioeconomic status and income, they could face more social and financial hardship, leading to their having more suicidal thoughts and behaviours.
They also mentioned that unhealthy lifestyle (eg binge drinking) has also been linked with lower IQ, and this could also affect frequency of suicidal thinking, plus other studies have also linked lower IQ with lower problem solving skills, and this could affect resilience to stress.
Another possibility is some research suggests that exposure to violence in childhood, either as a victim or a witness, can hamper IQ development as well as influence future suicide risk.
“Psychosis alters association between IQ and future risk of attempted suicide: cohort study of 1 109 475 Swedish men.”
G David Batty, Elise Whitley, Ian J Deary, Catharine R Gale, Per Tynelius, Finn Rasmussen.
Published online 3 June 2010
Written by: Catharine Paddock, PhD