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Study Casts Doubt on Low IQ’s Role in Early Death

Last Updated: July 02, 2009.

Adjustments for behavior dampen the negative effect, study finds.

THURSDAY, July 2 (HealthDay News) -- Low IQ alone doesn't increase a person's risk of early death, says a new study that challenges findings suggested by previous research.

The Swedish study of data on nearly 44,000 men found that other major factors -- such as mental health problems, risky behavior during adolescence and social circumstances as an adult -- nullify the effect of low IQ.

The study participants were born between 1949 and 1951 and called up for compulsory military service in 1969 and 1970. At that time, they underwent a comprehensive range of tests designed to produce an overall IQ score, as well as an assessment of their physical and mental health.

The men were tracked until 2003. A clear pattern emerged when IQ alone was used to analyze deaths among the men -- a low IQ was associated with a greater risk of dying between the ages of 40 and 54. Compared with men with the highest IQ scores, those with the lowest IQ scores were more than three times more likely to die early in middle age, the researchers found.

However, when the researchers added the other major risk factors to the analysis, the association between low IQ and increased risk of early death was greatly reduced. For example, adjusting for childhood factors weakened the association between low IQ and early death by 40 percent, and adding social factors in adulthood lowered the association by 73 percent.

The study appears online ahead of print in the Journal of Epidemiology and Community Health.

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SOURCE: BMJ Specialist Journals, news release, July 2, 2009