Higher IQ = Longer Life? Yes, say Swedish.

The Swedish do all the cool studies. I don't know what it is lately - every study I find that piques my interest seems to be of Swedish men.

Anyhow, we've already looked at whether your name affects your income, how about your IQ affecting your longevity?

A study of 1 million (yes, million) Swedish men has found a strong link between IQ scores in adulthood and mortality.

Apparently, one of the major causes of death is unintentional injury - things like poisonings, fire, falls and drownings. It's the leading cause of death for people under 45 years old. The study was done in Sweden because they, as it turns out, keep meticulous records on their populace. Like in the US, men have to register for a military draft, but in Sweden they take IQ scores when they do, which when combined with birth, death, and housing/census records means just about every able bodied man in the country has his age, health, socioeconomic status, cause of death and IQ recorded in accessible data. This gave the researchers a uniquely complete set of data to work with.

The scientists observed that in previous studies, the risk of fatal accidental death was much higher for those with low socioeconomic status. IQ, as it turns out, is also positively correlated with class - which makes sense, since those with more financial means are more likely to live in areas with better schools and/or afford a better education. So, logically, the researchers wanted to know if the two might be related - that is, lower IQs leading to more accidental deaths.

The results were clear. Those with lower IQs were significantly more likely to have died via accidents like falling or drowning than their 'smarter' peers. Compared with those in the highest IQ category, men in the lowest-scoring IQ category had a death rate from unintentional injury which was more than twice as high - almost six times as high for poisoning. The trend continued even when they corrected for economic class - that is, the stupid rich people were still more likely to die than the smart poor people, suggesting that the intelligence, not their financial situation, was a contributiong cause of their deaths. Of course, economic class still was a factor, but at least 19% (and as high as 86%) of the variation in risk could be attributed to differences in IQ.

Not that any of this is terribly surprising - it's just very interesting that its shown in such a large study. It's rare to have data for over a million men. Other studies with far fewer subjects have found similar results. One of the main reasons this correlation might exist between IQ and death has to do with access to healthcare. Higher intelligence leads to better jobs and thus better healthcare - those who make less and have either poor or no healthcare are more at risk of dying when something goes wrong. It's also possible that the job type is an important variable - those with higher IQ are able to attain more intellectual jobs, like academia, which are generally lower in accident risk than manual labor jobs, like working in a factory.

The other important finding of this study is that there was one variable that had a significant impact on risk despite IQ - education. So getting an education lowered the risk of fatal accidental injuries independent of IQ. This means that those who aren't the sharpest tool in the shed can still lower their risk of impaling themselves on one by working hard and getting through high school and college. Now if that's not a reason to stay in school, I don't know what is.

Batty, G., Gale, C., Tynelius, P., Deary, I., & Rasmussen, F. (2008). IQ in Early Adulthood, Socioeconomic Position, and Unintentional Injury Mortality by Middle Age: A Cohort Study of More Than 1 Million Swedish Men American Journal of Epidemiology, 169 (5), 606-615 DOI: 10.1093/aje/kwn381