Cognitive ability, education, height and body mass index in relation to risk of schizophrenia and mortality following its diagnosis

Abstract

This study examines the hypotheses that the traits of higher IQ, longer education and taller height are associated with lower risk of death as compared to traits of low IQ, short education, and short height in men with schizophrenia compared to men without schizophrenia. In total, 937,919 men born 1939-59 and 1983–1997 with information from conscription were followed for incident schizophrenia in Danish registries. Higher levels of cognitive ability, longer education, and taller height were associated with fewer cases of schizophrenia. In a sub-sample of 652,368 men with information on body mass index, underweight was associated with more and overweight and obesity were associated with fewer cases of schizophrenia compared with normal weight. Higher cognitive ability, longer education, and taller height were associated with fewer deaths from both natural and unnatural causes in both men with and without schizophrenia. Underweight was associated with more deaths from natural and unnatural causes, whereas overweight and obesity were associated with more deaths from natural causes and fewer deaths from unnatural causes in both groups of men. Due to interaction, tall height and long educational duration were associated with fewer deaths from natural causes, and obesity was associated with fewer deaths from unnatural causes among men with schizophrenia compared to men without. In conclusion, traits in young adulthood are associated with higher mortality in men with and without schizophrenia, but traits of long educational duration and obesity seem to be especially important for lower mortality in men with schizophrenia.