Research Roundup #2 – IQ in Anorexia

The following is my summary of “Estimated intelligence quotient in anorexia nervosa: a systematic review and meta-analysis of the literature” by Lopez et al (2010) in Ann Gen Psychiatry. I chose this article to help me better understand how I can simultaneously be an intelligent, rational person and someone who required treatment for something as irrational, and potentially fatal, as an eating disorder.

Introduction: The authors hypothesized that people with anorexia (AN) have a higher IQ level than the general population based on their better performance in school and clinical activities. However, this higher performance in AN patients could be due to higher perfectionism, rather than higher IQ. The authors further hypothesized that recovered AN patients have higher IQ scores than those in the acute phase of AN. Patients with higher IQs are more likely to complete treatment. The authors performed a systematic review and meta-analysis of AN intelligence literature.

Methods: The authors conducted the usual searches of science article databases (Medline, Embase, Psych Info, and ISI Web of Science) with terms like ‘IQ’, ‘anorexia’, and ‘eating disorders’, among others. All included studies had >10 participants and IQ measures for at least the full scale IQ (NART and Wechsler’s tests). Various statistical methods are described in more detail in the paper.

Results: Patients with eating disorders scored 10.8 units above the average IQ of normal controls, according to the NART (word-reading test with 50 short words of irregular pronunciation). There was no evidence of publication bias. Patients with eating disorders scored 5.9 units above the average IQ of normal controls, according the Wechsler’s IQ tests. There was higher heterogeneity in the Wechsler’s IQ results as well as some evidence of publication bias, but the results were still confirmed to be robust.

There was not a significant correlation between BMI and IQ.  However, those patients who have recovered from AN had higher IQ ranges than those with acute AN and normal controls.

Discussion: People with AN have higher average IQ scores than normal controls, especially as measured by the NART, which had less heterogeneity than the Wechsler’s tests. People who have recovered from AN have higher IQ scores than acute AN and normal controls; successfully treated AN patients may have higher IQ scores before treatment, supporting the hypothesis that higher IQ AN patients have a better treatment prognosis.

Limitations: The study was retrospective (only looked at past data). There was high variability in the Wechsler’s scales, interfering with analysis of those scales. There was a lack of literature about non-AN eating disorders (bulimia nervosa, eating disorder not otherwise specified, etc), making it difficult to generalize the findings across all eating disorders. Publication bias may exist because IQ performance was not the main outcome for many of the included studies.

Conclusions: Most studies show that AN patients have a higher average IQ than normal controls, which is yet higher in recovered AN patients. IQ should be assessed in the context of treatment and recovery.

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