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Lower IQ found in some adolescent psychiatric disorders

Lower IQ was associated with past-year fear and distress disorders and was not associated with PTSD, anxiety or eating disorders, according to recent findings.

“Modern examination of intelligence and psychiatric disorders has been primarily limited to relatively small, clinical samples,” Katherine M. Keyes, PhD, associate professor of epidemiology and codirector of the psychiatric epidemiology training program of Columbia University in New York, and colleagues wrote. “Poor performance on intelligence tests has been documented in individuals with attention-deficit/ hyperactivity disorder (ADHD), conduct disorder and oppositional defiant disorder, and PTSD. Associations of intelligence with depression and anxiety disorders are inconsistent across studies. The degree to which intelligence is associated with most psychiatric disorders remains an open question, given inherent biases in studies composed of clinical samples and the lack of population-based studies that measure intelligence.”

To determine associations between intelligence and psychiatric disorders, researchers analyzed a national sample of adolescents from the 2001 to 2004 National comorbidity Survey Replication-Adolescent Supplement (n = 10,073; mean age, 15.2 years).

Mean IQ was lower among adolescents with past-year bipolar disorder (P = .004), ADHD (P = .002), oppositional defiant disorder (P = .007), conduct disorder (P = .02), alcohol abuse (P < .001), drug abuse (P = .02) and specific phobia (P = .001), after adjusting for potential confounders.

Intelligence was not associated with PTSD, eating disorders or anxiety disorders other than specific phobia and was positively associated with past-year major depression (P = .01).

Associations between fluid intelligence with lifetime disorders that remitted were lower than associations with past-year disorders, except for separation anxiety disorder.

Among all assessed disorders, higher disorder severity was associated with lower fluid intelligence. Adolescents with severe specific phobia had a mean IQ 4.4 points lower than those with less severe specific phobia (P < .001).

Mean IQ was 5.6 points lower among adolescents with severe alcohol abuse vs. those without severe abuse (P < .001).

“Together, these findings reflect the potential role of cognitive factors in the etiology of diverse forms of psychiatric disorders, as well as how mental disorders may influence cognitive ability. Most importantly, this work highlights the critical importance of early identification and treatment of mental disorders in youth and the potential utility of accommodations in school settings for children with a wide range of psychiatric disorders to promote long-term success,” the researchers concluded. – by Amanda Oldt

Disclosure: Keyes reports no relevant financial disclosures. Please see the study for a full list of relevant financial disclosures.