The studies on intelligence and longevity all agree that those with high IQs live longer. One of these studies, the Swedish Conscript Study, is especially impressive since it includes practically all Swedish men born between 1950 and 1976 – making the number of participants just under one million. They all took an intelligence test which uses a nine grade scale. Those scoring 9 were 20 years later shown to have a 70 percent less risk of mortality than those scoring a 1.
This may sound like something obvious – people with high intelligence come from better homes and have been brought up by parents who give them more fruit and vegetables and less pizza and soft drinks. However, it was shown that adjusting for things like parental socioeconomic status as well as blood pressure, weight, physical illness at conscription, the risk of mortality for those with the highest intelligence was still reduced by 60 percent compared to those with the lowest intelligence. This is really worth noticing – social background makes up less than 10 percent of the reduced risk of mortality. This is partly explained by the fact that the men were in their 40s at the follow-up, and few die from cardiovascular disease at that age. But it’s still interesting to note that social background is such a little factor in overall mortality.
So while it’s known that intelligent people engage in health behaviors – eating vegetables, exercising, following the doctor’s orders when ill. It’s reasonable to suspect that a healthy lifestyle is the mediator between IQ and longevity, even though this lifestyle is probably more a matter of personal decision than upbringing. It accords well with the connection between IQ and death in cardiovascular disease, the biggest killer. But if we look at cancer, the second biggest killer, the connection with intelligence is weak or non-existent. For skin cancer it’s even inversed. How can that be?
I haven’t found any explanation for this paradox in the literature, but looking at the causes of these two killers it’s clear that cardiovascular disease is related to stress in a way that cancer is not. And stress is a lot about lack of control. It’s a well-known fact that those prone to stress, that is those having the trait neuroticism, have more heart disease. This idea is supported by another large study, called the Vietnam Experience Study, which looked at mortality of veterans and found that the more neurotic a veteran was the more a high intelligence would lower his mortality.
This suggests that a major part of why intelligence promotes health is in that it protects against the harmful effects of stress and thus against cardiovascular disease. How? It could be that they use their intelligence to cope with stressful events better. It may also be a matter of what some researchers call system integrity. A high intelligence, according to this theory, is an indication of a generally more robust and well built organism that doesn’t break under pressure as easily as the average. Although this has been hard to prove some studies have found that reaction time, as a proxy for system integrity, account for most of the correlation between intelligence and mortality. It could of course also be a combination of stress handling ability and system integrity.
All of these interesting findings are found in the relatively new field of cognitive epidemiology. While it doesn’t disprove that eating lots of vegetables is good for you (it really is) it shows that this may be of less importance than most of us imagine compared to stress – our proneness to it in form of neuroticism, but perhaps even more important how we cope with it, both psychologically and in terms of biological hardiness.