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

Objectives- To examine the association between measured childhood intelligence 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 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 standard deviation (~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<.001) were observed for: accidental deaths (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 non-smoking-related cancer deaths (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, 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 to 26%) on controlling for potential confounders, including three childhood socioeconomic status indicators. In a replication sample from Scotland, of a similar birth-year cohort and follow-up period, smoking and adult socioeconomic status partially attenuated (16 to 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 years, higher scores on a well-validated childhood intelligence test were associated with lower mortality risk ascribed to coronary heart disease and stroke, smoking-related cancers (particularly lung and stomach), respiratory diseases, digestive diseases, accidental death, and dementia.