Higher IQ Found in Patients With Anorexia Nervosa

Susan Kreimer

December 29, 2010

December 29, 2010 — Researchers have detected a link between body mass index and intelligence quotient (IQ) in patients with anorexia nervosa (AN).

The systematic review and meta-analysis of 30 peer-reviewed studies appears online December 23 in the Annals of General Psychiatry.

Testing the hypothesis that people with AN have a higher IQ than the general population, the researchers — led by Carolina Lopez, MSc, from the Institute of Psychiatry, Kings College London in the United Kingdom and Facultad de Medicina de la Universidad de Chile in Santiago — set out to appraise the research into reported IQ levels. They searched the terms intelligence quotient, IQ, intelligence, cognition, eating disorders, and anorexia in electronic databases.

A total of 30 peer-reviewed studies, which included 849 patients diagnosed with AN, used well-established IQ measures; 14 studies used the National Adult Reading Test, and 16 studies used the Wechsler Intelligence Scales. On these tests, people with AN scored 10.8 units and 5.9 units above the average IQ of the normative population, respectively.

The researchers also found that people who have recovered from AN demonstrated scores on well-validated IQ tests superior to those of patients in the acute phase of illness and the normative population. Mean IQ ranged from 109.3 to 118.1 compared with 96.1 to 117.6 in women with current AN. However, the small number of studies of women with a past history of AN did not allow for a formal meta-analysis.

"The benefit of this appraisal of current knowledge will help researchers in planning future studies and formulate important questions, such as: do patients with higher IQ have better prognosis? How could high IQ be effectively used in psychological treatment? Is IQ decline evident in AN?" the authors note. "Whereas the most obvious reason will be malnutrition, none of the studies so far have used premorbid and current IQ measures simultaneously."

Comparison groups should be carefully selected in future studies on AN, the authors add, "because IQ will be an important contributing factor in social cognition [and] cognitive tasks, either using self-report or experimental instruments."

The authors acknowledge their review's limitations, including its retrospective design. In addition, the results of studies using Wechsler's tests showed high heterogeneity, making it difficult to draw strong conclusions. Another concern stems from the possibility of volunteer samples in these studies being highly selected, consisting of people seeking treatment in clinics or being willing to participate in research. Although this may relate to higher education and IQ performance, the researchers say such questions are beyond the study's scope.

"IQ in AN is at least as high as the average IQ found in the normative population and most studies show that this group have a high average IQ," the authors conclude. "There is a preliminary but important observation about IQ in the recovered population, which is that this group may represent a group with higher IQ than norms and current AN groups, opening the question about the influence of this factor on treatment and recovery. We think that exploring IQ in the context of treatment and recovery may provide useful information for clinicians and researchers."

The study was supported by the United Kingdom's National Institute for Health Research. The authors have disclosed no relevant financial relationships.

Ann Gen Psychiatry. Published online December 23, 2010.

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