April 5, 2001 -- Call it revenge of the nerds: People who are smarter than their peers in late childhood appear to have a greater chance of living longer, at least until age 76, Scottish researchers say. But whether the disparities in life span are due to social differences, health reasons, or simply knowing enough to come in out of the rain is unclear.
In 1932, a group of 2,230 people took an intelligence test when they were 11-year-old students in Aberdeen, Scotland. Those who died before Jan. 1, 1997, (at or before age 76) had significantly lower IQ scores than survivors. The effect was weaker among men than among women. In fact, the effect was reversed in men during World War II, when men with high IQs were more likely to have died in active service, write Lawrence J. Whalley, PhD, and Ian J. Deary, PhD, in the April 6 issue of the British Medical Journal.
"Our data show that high mental ability in late childhood reduces the chance of death up to age 76 years," the researchers write. "In our study, women with a deficit in IQ of 15 points at age 11 had less than 75% survival, and those with a deficit of 30 points were about half as likely to survive."
There are many possible explanations for why they found such marked differences in survival between people with lower and higher IQs.
"Causes of death were very much as expected. Most died of cancer, heart disease, and stroke. The link between lower childhood IQ and these common causes of death may be because of childhood factors that predispose to both disease and lower IQ. Alternatively, perhaps children with lower IQ grow up to become adults less able to avoid disease or get help when they need it," says Whalley in a written statement.
An expert in aging and long-term care, who reviewed the study for WebMD, offers an alternative explanation. "Presumably, people who have higher IQs on average probably got better jobs and had a better social class than people who didn't," says Robert Kane, MD, professor of health services research and policy at the University of Minnesota in Minneapolis. He suggests that the social and economic advantages acquired by higher intellect could have either direct or indirect influences on health and longevity.
Kane and colleagues previously had studied death rates among Catholic nuns in Mankato, Minn., and found that sisters who held at least a bachelor's degree were more likely than others to survive to old age while remaining able to care for themselves. That study and subsequent studies also suggested that those who were more mentally active were less likely to develop serious dementia.
Whalley and Deary mention that "the adoption of healthy behaviors in adulthoods" and "access to safer environments" also may explain their results.
But they also caution against reading too much into the results.
"It's not so much that IQ is a very important factor," says Deary in a written statement, "it's more that it has been a missing element in other studies which looked at education and social class effects on health. The IQs taken at age 11 in 1932 were just a quick snapshot of the children's performance during a 45-minute test. It is remarkable that these scores should have a relation to how long they lived. What we need to do now is understand this link between IQ and survival. We've done the easy bit; the hard work comes in unraveling the reasons for the link."