The Smart Ones are Living Longer
A child with a high IQ is more likely to get good grades, be accepted to a prestigious college, accrue successes in life and career, and make healthy lifestyle choices compared to lower-IQ peers. Now, a Swedish study published in the British Medical Journal (BMJ) concludes that children with a high IQ also have a reduced risk of mortality as adults.
Many studies have shown similar associations between adult IQ and mortality, but the Swedish study is one of only a handful to link intelligence and cognitive performance at a young age — 10 years in this study — to decreased mortality in adulthood. Many similar studies have been inconclusive to date; the brain continues to develop and change in emotional and cognitive ability and performance until approximately 20 years of age, making early IQ tests somewhat difficult to interpret. However, the newest study published in the BMJ followed more than 1500 children for 65 years and found a significant association between high intelligence at age 10 and education attainment and decreased risk of all-cause mortality. Interestingly, this association was strongest in males, and high IQ was associated with decreased mortality, even after adjusting for education attainment and paternal education — 2 other indicators of mortality. Women, however, did not experience the same association. Women with an above average IQ actually had a higher risk of mortality, after adjusting for other factors, but only after age 60.
Noting the gender differences in the findings, the authors speculate that mortality cannot simply be explained by IQ, but involves the social and physical environment as well. Most other studies investigating a link between IQ and mortality have offered similar remarks. From a very early age, even before birth, parental education, socioeconomic status, and lifestyle choices influence the cognitive ability of children. For example, mothers with more education are more likely to breastfeed their children, and breast milk correlates significantly with total brain volume and high IQ scores. Education and nutrition during the preschool years are also associated with increased IQ. Similarly, children with parents who were more involved in their education and social choices have a decreased risk of mortality in adulthood. To the same point, children with disengaged and uninvolved parents are more likely to engage in risky behavior and delinquency, which accounts for some of the association between increased risk of mortality and lower IQ.
Still, it is impossible to say that scoring well on an IQ test has a direct link to mortality risk. While high IQ is associated with decreased risk factors for early mortality and unhealthy lifestyle choices, including smoking, heavy alcohol consumption, and overweight and obesity, the association is weakened after adjusting for socioeconomic status. Still, increased physical fitness is linked to high IQ, and improving fitness leads to increased cognitive performance. Adults with high IQ are also less likely to experience depression, and have a significantly reduced risk of many diseases and health conditions. Further, as adults, those with lower IQ are more likely to die from injuries such as poisonings, fire, falls, drowning, and road injuries than those with higher IQ. Quite possibly, childhood IQ is not a cause, per se, of mortality, but a marker for social status and class later in life, which is an indicator of risk of death and illness. The socioeconomic inequalities in access to healthcare may explain a portion of the increased mortality among lower IQ adults.
Or, the association between high intelligence and decreased mortality could be real and causative. Is it another case of survival of the fittest? Is nature getting rid of those who swim in the shallow end of the proverbial gene pool? Probably not. While high IQ at an early age may be an indication of a strong, fit body to begin with, cognitive skills should be fostered and nourishing childhood environments should be promoted to encourage healthy behaviors and choices later in life.
Aberg, M., Pedersen, N., Toren, K., Svartengren, M., Backstrand, B., Johnsson, T., Cooper-Kuhn, C., Aberg, N., Nilsson, M., & Kuhn, H. (2009). Cardiovascular fitness is associated with cognition in young adulthood Proceedings of the National Academy of Sciences, 106 (49), 20906-20911 DOI: 10.1073/pnas.0905307106
Batty, G., Deary, I., & Macintyre, S. (2007). Childhood IQ in relation to risk factors for premature mortality in middle-aged persons: the Aberdeen Children of the 1950s study Journal of Epidemiology & Community Health, 61 (3), 241-247 DOI: 10.1136/jech.2006.048215
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
Batty, G., Shipley, M., Mortensen, L., Boyle, S., Barefoot, J., Gronbaek, M., Gale, C., & Deary, I. (2008). IQ in late adolescence/early adulthood, risk factors in middle age and later all-cause mortality in men: the Vietnam Experience Study Journal of Epidemiology & Community Health, 62 (6), 522-531 DOI: 10.1136/jech.2007.064881
Batty, G., Wennerstad, K., Smith, G., Gunnell, D., Deary, I., Tynelius, P., & Rasmussen, F. (2009). IQ in Early Adulthood and Mortality By Middle Age Epidemiology, 20 (1), 100-109 DOI: 10.1097/EDE.0b013e31818ba076
Der, G., Batty, G., & Deary, I. (2009). The association between IQ in adolescence and a range of health outcomes at 40 in the 1979 US National Longitudinal Study of Youth Intelligence, 37 (6), 573-580 DOI: 10.1016/j.intell.2008.12.002
Hart, C. (2003). Childhood IQ, Social Class, Deprivation, and Their Relationships with Mortality and Morbidity Risk in Later Life: Prospective Observational Study Linking the Scottish Mental Survey 1932 and the Midspan Studies Psychosomatic Medicine, 65 (5), 877-883 DOI: 10.1097/01.PSY.0000088584.82822.86
Isaacs EB, Fischl BR, Quinn BT, Chong WK, Gadian DG, Lucas A. Impact of breast milk on IQ, brain size and white matter development. Pediatr Res. Dec 22 2009.
Gordon, A. (2008). Breastfeeding, Breast-Milk Feeding, Breast Feeding, and IQ: Unknown and Known Knowns Archives of General Psychiatry, 65 (12), 1457-1458 DOI: 10.1001/archpsyc.65.12.1457
Lager, A., Bremberg, S., & Vagero, D. (2009). The association of early IQ and education with mortality: 65 year longitudinal study in Malmo, Sweden BMJ, 339 (dec11 1) DOI: 10.1136/bmj.b5282