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Lower Childhood IQ Associated With Higher Risk Of Adult Mental

ScienceDaily (Dec. 1, 2008) — Researchers have hypothesized that
people with lower IQs may have a higher risk of adult mental
disorders, but few studies have looked at the relationship between low
childhood IQ and psychiatric disorders later in life.

In a new, long-term study covering more than three decades,
researchers at Harvard School of Public Health (HSPH) found that
children with lower IQs showed an increased risk of developing
psychiatric disorders as adults, including schizophrenia, depression
and generalized anxiety disorder. Lower IQ was also associated with
psychiatric disorders that were more persistent and an increased risk
of having two or more diagnoses at age 32.

The study participants were members of the Dunedin Multidisciplinary
Health and Development Study, a cohort of children born in 1972-1973
in Dunedin, New Zealand. At the initial assessment at age 3, the study
had 1,037 children. The participants were also interviewed and tested
on their overall health and behavior at ages 5, 7, 9, 11, 13, 15, 18,
21, 26 and at age 32, when 96% of the original cohort participated.
IQs were assessed at ages 7, 9 and 11. Psychiatric disorders were
assessed at ages 18 through 32 in interviews by clinicians who had no
knowledge of the subjects' IQ or psychiatric history.

The authors used IQ as a marker of a concept called cognitive reserve,
which refers to variation between people in their brain's resilience
to neuropathological damage.

The results showed that lower childhood IQ predicted an increased risk
of a variety of adult mental disorders. "Lower childhood IQ predicted
increased risk of schizophrenia, depression, and generalized anxiety
disorder. Individuals with lower childhood IQ also had more persistent
depression and anxiety and were more likely to be diagnosed with two
or more disorders in adulthood," said lead author Karestan Koenen,
assistant professor of society, human development, and health at HSPH.

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