Childhood intelligence in relation to major causes of death in 68 year follow-up: prospective population study

Abstract

Objectives To examine the association between intelligence measured in childhood and leading causes of death in men and women over the life course. Design Prospective cohort study based on a whole population of participants born in Scotland in 1936 and linked to mortality data across 68 years of follow-up. Setting Scotland. Participants 33 536 men and 32 229 women who were participants in the Scottish Mental Survey of 1947 (SMS1947) and who could be linked to cause of death data up to December 2015. Main outcome measures Cause specific mortality, including from coronary heart disease, stroke, specific cancer types, respiratory disease, digestive disease, external causes, and dementia. Results Childhood intelligence was inversely associated with all major causes of death. The age and sex adjusted hazard ratios (and 95% confidence intervals) per 1 SD (about 15 points) advantage in intelligence test score were strongest for respiratory disease (0.72, 0.70 to 0.74), coronary heart disease (0.75, 0.73 to 0.77), and stroke (0.76, 0.73 to 0.79). Other notable associations (all P<0.001) were observed for deaths from injury (0.81, 0.75 to 0.86), smoking related cancers (0.82, 0.80 to 0.84), digestive disease (0.82, 0.79 to 0.86), and dementia (0.84, 0.78 to 0.90). Weak associations were apparent for suicide (0.87, 0.74 to 1.02) and deaths from cancer not related to smoking (0.96, 0.93 to 1.00), and their confidence intervals included unity. There was a suggestion that childhood intelligence was somewhat more strongly related to coronary heart disease, smoking related cancers, respiratory disease, and dementia in women than men (P value for interactions <0.001, 0.02, <0.001, and 0.02, respectively).Childhood intelligence was related to selected cancer presentations, including lung (0.75, 0.72 to 0.77), stomach (0.77, 0.69 to 0.85), bladder (0.81, 0.71 to 0.91), oesophageal (0.85, 0.78 to 0.94), liver (0.85, 0.74 to 0.97), colorectal (0.89, 0.83 to 0.95), and haematopoietic (0.91, 0.83 to 0.98). Sensitivity analyses on a representative subsample of the cohort observed only small attenuation of the estimated effect of intelligence (by 10-26%) after adjustment for potential confounders, including three indicators of childhood socioeconomic status. In a replication sample from Scotland, in a similar birth year cohort and follow-up period, smoking and adult socioeconomic status partially attenuated (by 16-58%) the association of intelligence with outcome rates. Conclusions In a whole national population year of birth cohort followed over the life course from age 11 to age 79, higher scores on a well validated childhood intelligence test were associated with lower risk of mortality ascribed to coronary heart disease and stroke, cancers related to smoking (particularly lung and stomach), respiratory diseases, digestive diseases, injury, and dementia.

Childhood IQ and mortality during 53 years’ follow-up of Swedish men and women

“…In one of few studies reporting on cause-specific mortality separately for men and women, on a US cohort of 10 000 participants followed to age 70, the association with CVD mortality was comparatively weak—less than HR 1.2—in both genders,26 thus more similar to our findings in women. In the SMS study, however, the associations were instead stronger in women (HR 1.43)12 and more similar to the magnitude in men in our study.…”

“…In contrast, mediators in adult life seem to have a crucial role in the association with mortality, and they could therefore be subject to societal interventions. In terms of more specific pathways, the associations found in several studies between IQ and smoking-related causes of mortality, such as smoking-related cancers8 12 24 and CVD,3 8 12 28 29 suggest that smoking is on the pathway between IQ and mortality 12. In the present study, the associations between IQ and these outcomes weakened in men and disappeared in women when their social status was taken into account.…”

“…In contrast, the largest study to date, including nearly 1 million Swedish men in mandatory military conscription, found no evidence of associations of IQ with all cancers or, for example, lung cancer 23. However, results have varied between cohorts,3 24–26 and smoking-related cancers were associated with IQ in both men and women in the SMS cohort (HRs, lung cancer: 1.30 and 1.43, respectively; other smoking-related cancers: 1.19 and 1.27, respectively) 12. We found associations between IQ and lung cancer in men and women, but a clear association with other smoking-related cancers in men only.…”

The new genetics of intelligence

“…Intelligence also spills over into many aspects of everyday life such as the selection of romantic partners and choices about health care1. This is why intelligence — often called general cognitive ability2 — predicts educational outcomes3, occupational outcomes4,5 and health outcomes6 better than any other trait. It is also the most stable psychological trait, with a Pearson correlation coefficient of 0.54 from age 11 years to age 90 years7.…”

A combined analysis of genetically correlated traits identifies 187 loci and a role for neurogenesis and myelination in intelligence

“…In a population with a range of cognitive ability, intelligence accounts for around 40% of the variation between individuals in scores on diverse cognitive tests [2]. Intelligence is predictive of health states, including mortality; [3,4] a lower level of cognitive function in youth is associated with earlier death over the next several decades [5]. Intelligence is a heritable trait, with twin-and family-based estimates of heritability indicating that between 50-80% of differences in intelligence can be explained by genetic factors [6].…”