Few previous studies have assessed the association of measures of intelligence with suicide, and results have often conflicted.
Researchers analysed the results of four intelligence tests, performed at conscription into military service, for 987,308 Swedish men. The men were monitored for up to 26 years and suicides were recorded.
Better performance on the tests was associated with a reduced risk of suicide. The strongest associations were with the logic test score, where the risk of suicide was three times higher in the lowest compared with the highest scorers.
The strength of the link and the large sample size suggest that this finding is unlikely to be due to chance, they add. One possible explanation could be that influences on brain development during childhood also increase an individual's susceptibility to mental illness and hence suicide. Alternatively, it may be due to an individual's ability to solve problems in times of crisis or maladjustment in childhood, they conclude.