Summary: A new study reports higher intelligence in children is associated with a reduced risk of developing chronic diseases such as heart disease, smoking related cancers and dementia. After taking several confounders into account, the researchers found higher IQ in childhood was associated with a lower risk of death until the age of 79.
Higher intelligence (IQ) in childhood is associated with a lower lifetime risk of major causes of death, including heart disease, stroke, smoking related cancers, respiratory disease and dementia, finds a study published by The BMJ today.
It is the largest study to date reporting causes of death in men and women across the life course, and the findings suggest that lifestyle, especially tobacco smoking, is an important component in the effect of intelligence on differences in mortality.
Previous studies have shown that, on average, individuals with higher IQs tend to live a little longer than those with lower IQs, but these are largely based on data from male conscripts followed up only to middle adulthood.
So a team of researchers from the University of Edinburgh set out to examine the association between intelligence test scores measured at age 11 and leading causes of death in men and women up to age 79.
Their findings are based on data from 33,536 men and 32,229 women born in Scotland in 1936, who took a validated childhood intelligence test at age 11, and who could be linked to cause of death data up to December 2015.
Cause of death included coronary heart disease, stroke, specific cancers, respiratory disease, digestive disease, external causes (including suicide and death from injury), and dementia.
After taking account of several factors (confounders) that could have influenced the results, such as age, sex and socioeconomic status, the researchers found that higher childhood intelligence was associated with a lower risk of death until age 79.
For example, a higher test score was associated with a 28% reduced risk of death from respiratory disease, a 25% reduced risk of death from coronary heart disease, and a 24% reduced risk of death from stroke.
Other notable associations were seen for deaths from injury, smoking related cancers (particularly lung and stomach), digestive disease, and dementia. There was no evident association between childhood intelligence and death from cancers not related to smoking.
The authors outline some study limitations which could have introduced bias. However, key strengths include the whole population sample, 68-year follow up, and ability to adjust for important confounders.
They also point out that significant associations remained after further adjustment for smoking and socioeconomic status, suggesting that these factors did not fully account for mortality differences. And they say future studies “would benefit from measures of the cumulative load of such risk factors over the life course.”
This study is the largest to date reporting causes of death across the life course, and it provides us with interesting results, say researchers based in Sweden, in a linked editorial.
“Importantly, it shows that childhood IQ is strongly associated with causes of death that are, to a great extent, dependent on already known risk factors,” they write. And they suggest that “tobacco smoking and its distribution along the socioeconomic spectrum could be of particular importance here.”
In conclusion, they say: “It remains to be seen if this is the full story or if IQ signals something deeper, and possibly genetic, in its relation to longevity.”
Source: Melissa Cochrane – BMJ
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Full open access research for “Childhood intelligence in relation to major causes of death in 68 year follow-up: prospective population study” by Catherine M Calvin, G David Batty, Geoff Der, Caroline E Brett, Adele Taylor, Alison Pattie, Iva Čukić, and Ian J Deary in BMJ. Published online
June 28 2017 doi:10.1136/bmj.j2932
Childhood intelligence in relation to major causes of death in 68 year follow-up: prospective population study
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.
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 intelligence in relation to major causes of death in 68 year follow-up: prospective population study” by Catherine M Calvin, G David Batty, Geoff Der, Caroline E Brett, Adele Taylor, Alison Pattie, Iva Čukić, and Ian J Deary in BMJ. Published online
June 28 2017 doi:10.1136/bmj.j2932