Clever people live longer. Those who possess high childhood IQs (intelligence quotients) tend to survive to a riper old age than peers who score less well, according to research published last week in the British Medical Journal (BMJ).
While similar positive associations between cognitive ability and health have been observed before — those with degrees, for example, tend to be longer-lived than those without — this paper has inspired discussion of a radical theory that is barely known outside a small coterie of researchers.
The “system integrity” theory contends that high-IQ individuals are not just healthier because they are better at heeding health advice, such as to stop smoking, or earn more (well-paid professions might offer safer working environments and better healthcare).
Rather, they might be genetically blessed with an exceptional physiology — and this “optimal bodily functioning” leads to both a high IQ and resistance to disease.
It revives thinking that goes back almost a century. In 1920, the principal of an Illinois school gave his pupils a well-known intelligence test, and then asked the school nurse for the health records of the 40 highest scorers and the 40 lowest.
The most able, he noted, had the cleanest bills of health, which “adds something to the accumulating evidence that the child of good intellectual ability is also of good physical ability”.
The pioneering psychologist, Charles Spearman, who formulated early ideas for measuring intelligence at the start of the 20th century, also pondered whether some truth lay behind the maxim “mens sana in corpore sano” (a healthy mind in a healthy body).
The BMJ research comes from the laboratory of Professor Ian Deary, professor of differential psychology at Edinburgh University. Prof Deary grasped the potential of the Scottish Mental Surveys of 1932 and 1947, which in those years recorded the intelligence test scores of nearly every 11-year-old in Scotland.
By following the children into adulthood, then looking at the causes of death of those in the group, scientists could examine the correlation between childhood intelligence, as measured by IQ, and future health.
This study, lead-authored by his colleague Ms Catherine Calvin, focused on more than 65,000 Scots tested in 1947. Nearly half were still alive, aged 79, when the survey was conducted in 2015.
Ms Calvin and colleagues showed that higher IQs at 11 were associated with lower death rates in coronary heart disease, stroke, smoking-related cancers, respiratory diseases, digestive diseases, injury and dementia.
Those in the highest tenth of IQ had half the risk of developing certain conditions, including coronary heart disease and stroke, than those in the bottom tenth.
High scorers, then, find themselves more immune than their lower-IQ classmates to the commonest slings and arrows of medical misfortune. The link between high IQ and longer lifespan, seen in both men and women, persists even when factors such as higher incomes and lifestyle (for example, smoking) are accounted for.
The stubbornness of that correlation, seen in previous, smaller studies, has led to a new field: Cognitive epidemiology, which explores the role of early intelligence as a risk factor for health in adulthood.
And one idea being floated by cognitive epidemiologists is that genetics could be the unseen hand behind both a high IQ and a hardy constitution.
In short, genetics might be the key to system integrity. To study this, researchers recently sifted through data on same-sex twins, where at least one twin had died.
The three twin registries — from the United States, Finland and Sweden — all contained cognitive test scores from either childhood or early adulthood. The aim of the study was to discover whether the longer-lived twin was also the higher scorer. Broadly, among both identical and non-identical pairs, the brighter twin tended to live longer. The effect was greater in non-identical twins (who share 50 per cent rather than 100 per cent of their genes).
The research was published last year in the International Journal of Epidemiology under the provocative title: “The association between intelligence and lifespan is mostly genetic.”
When I came to write this column, I wondered why I had never heard of the concept of system integrity in human health. On reflection, the reasons are obvious.
It is a very difficult theory to test, given the multiple ways that intelligence can affect health, such as by influencing education and occupation (simply planning a healthy lifestyle could be viewed as a cognitive challenge).
Any underlying physiological phenomenon would be hard to tease out with confidence. But it also brings together several deeply controversial concepts: The genetics of intelligence, IQ tests and the idea of biological determinism.
If genes influence both intelligence and health, as evidence suggests, then our life outcomes — and even the timings of our deaths — are partly set by the circumstances of our birth. This is uncomfortable territory, because it suggests policy interventions cannot easily iron out health disparities.
Prof Deary acknowledged this aspect of the debate when he once said that unveiling early IQ as a predictor of both health and death to socially-minded epidemiologists was like “parading a clever but noisily disobedient and mucky child before staid and suspicious relatives ... but this is too important a finding to allow it to get lost in controversy”.
That cognitive ability is correlated with health is now beyond doubt.
Whether that link is an outward sign of a fundamental bodily difference, only future studies will tell. FINANCIAL TIMES
ABOUT THE AUTHOR:
Anjana Ahuja is a contributing writer on science for the Financial Times.