Associations between childhood intelligence (IQ), adult morbidity and mortality

Intelligence is a life-long trait that exerts powerful influences on educational success, occupational status, use of health services, life style and recreational choices. Until recently, the influence of cognitive performance on time to death was thought largely to be based on failing cognition in the time immediately before death or because lower mental ability was associated with low socioeconomic status and socioeconomic disadvantage. Children who were systematically IQ tested early in the twentieth century have now completed most of their life expectancy and permit evaluation of a possible link between childhood IQ and survival. This link is discussed as it affects people with intellectual disability and as a possible contributor to the acquisition of a healthy life style or use of health services. Studies on the topic are affected by many methodological pitfalls. Recently, as cohorts IQ tested as adolescents have completed middle age, new relevant data have become available. These suggest that earlier attempts to tease out the confounding effects of socioeconomic status on the relationship between childhood IQ and mortality did not take account of the full effects of childhood adversity on IQ and disease risk. When statistical models that include childhood adversity are tested, these attenuate and sometimes remove the contribution of IQ to morbidity and premature death.