Scotland’s University of Edinburgh researchers in a report in BMJ published their findings that higher childhood intelligence is linked to a lower chance of dying before the age of 80.
The report describes how higher scores on childhood IQ tests were linked to a lower lifetime risk of dying from known major causes, including heart disease, stroke, digestive disease, external causes of death, respiratory diseases, and dementia.
For these diseases, the reductions in risk were largely similar for men and women. But the researchers also found that, in men only, a higher childhood IQ was linked to a lower risk of suicide.
The researchers say that the findings suggest that lifestyle – and smoking in particular – is an important factor in the link between childhood IQ and risk of death.
Previous studies have already suggested that people who score higher on intelligence tests tend to live longer, on average, than the people with lower scores. However, most of these do not span the life course, or they only focus on particular groups.
As well as finding a link between higher childhood IQ and lower risk of dying before the age of 80, the researchers found that the amount of reduced risk varies by cause of death.
For instance, their analysis reveals that a higher score on childhood IQ tests is linked to a 24 per cent lower risk of dying from stroke, a 25 per cent lower risk of dying from coronary heart disease, and a 28 percent lower risk of dying from the respiratory disease.
The team also found links between higher childhood IQ and lower risk of death from injury, dementia, digestive diseases, and smoking-related cancers such as lung and stomach cancer.
However, they found no evidence of a link between childhood IQ and death from cancers that are not related to smoking.
When they adjusted the results to take into account smoking and socio-economic status, the researchers found that some of the links remained strong, suggesting that these factors do not fully explain the differences.
They suggest that future studies should now investigate the “cumulative load of such risk factors over the life course.”
They draw attention to a section of the study report that looks at how increments in childhood intelligence relate to specific causes of death. They liken it to a drug trial that looks at the effect of different doses.
“The most obvious dose-response relations are those for cardiovascular disease, coronary heart disease, stroke, smoking-related cancer, and respiratory disease,” they note.
Although “injuries could also be added to this list,” they remark that, nevertheless, the study “tells us that lifestyle, and especially tobacco smoking, must be an important component in the effect of intelligence on differences in mortality.” They conclude:
