Those who exhibited high intelligence in their childhood years have a reduced lifetime risk for the top causes of death like heart disease, respiratory disease, stroke, dementia and smoking-related cancers. This finding was recently published in The BMJ.
About the Study
A group of University of Edinburgh researchers sought to study the association between IQ scores gauged at 11 years-old and the top causes of death in people upwards of age 79. It is the largest study centered on reporting the causes of death throughout the course of life. The findings show that lifestyle, especially smoking tobacco, is a critically important factor in the effect of IQ on differences in lifespan. Prior studies showed that those with improved intelligence tended to live slightly longer than individuals with less intelligence. However, these studies were mainly based on information derived from male conscripts tracked to the mid-adulthood years.
The findings were derived from data from more than 33,000 men and over 32,000 women born in Scotland back in 1936. These individuals took a childhood intelligence exam at age 11. Their cause of death was identified up to December of 2015. Causes of death for these individuals ranged from stroke to heart disease, digestive disease, cancer, dementia and external causes like suicide or death resulting from an injury.
The Results
Once a number of different factors (age, socioeconomic status, sex) that had the potential to impact the results were accounted for, the research team determined that those who had a higher childhood IQ score enjoyed a decreased risk of death until the age of 79. As an example, a high score on the childhood IQ test was tied to a 28 percent decrease in risk of death due to respiratory disease. A high score was associated with a 25 percent reduction in risk of death induced by coronary disease. Those who scored high on the childhood IQ test had a 24 percent reduction in risk of death stemming from a stroke.
Other important associations were found for deaths from dementia, digestive disease, injury and cancers related to smoking. There was no association between IQ score and death from cancers that did not relate to smoking.
Why the Study has Merit
Though the study’s authors identified study limitations that had the potential to introduce bias, the study is widely considered to be meritorious. The large population sample combined with the 68-year follow-up along with the adjustment for vitally important co-founders gives the study credence. Key associations were intact after additional adjustments for smoking as well as socioeconomic status. This suggests that such factors do not completely account for differences in mortality. Additional studies should consider measures of the cumulative load of these risk factors across the life course.
It can be concluded that childhood intelligence is strongly tied to causes of death that are dependent on previously identified risk factors. The study suggests smoking and its distribution across the socioeconomic spectrum is critically important. Yet it is undetermined if this study tells the whole story or if intelligence indicates something deeper. Perhaps there is a genetic basis to IQ’s relation to lifespan.
