Higher IQs Found in Patients with AN

With recovery, IQs rose.

Researchers have detected a link between body mass index (BMI; kg/m²) and intelligence quotient (IQ) in patients with anorexia nervosa (AN). One finding was that IQ fluctuated with BMI levels.

Carolina Lopez, MSc, from the Institute of Psychiatry, Kings College, London, and colleagues at Facultad de Medicina de la Universidad de Chile, Santiago, reviewed 30 peer-reviewed studies to test the hypothesis that people with AN have higher IQs than the general population. They searched the terms intelligence quotient, IQ, intelligence, cognition, eating disorders, and anorexia in electronic databases (Ann Gen Psychiatry 2010; 9:40). The authors also hypothesized that people with a past history of AN, now recovered, would show higher IQ scores than those who were in the acute phase of AN and the normative population.

The 30 peer-reviewed studies included 849 patients diagnosed with AN. Fourteen 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 recovered from AN demonstrated scores on well-validated IQ tests that were superior to those of patients in the acute phase of illness and the normative population. Mean IQs ranged from 109.3 to 118.1, compared with 96.1 to 117.6 in women who currently had AN. However, the small number of studies of women with a past history of AN did not allow for a formal meta-analysis.

Does higher IQ point to a better prognosis?

The results of this study may help researchers plan future studies and formulate important questions, such as: Do AN patients with higher IQs have a better prognosis? How could high IQs be effectively used in psychological treatment? Is there an evident decline in IQ in persons with AN? The authors noted that whereas the most obvious reason for a change in IQ would probably 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 added, because IQ will be an important contributing factor in social cognition [and] cognitive tasks, either using self-report or experimental instruments.

The authors acknowledged 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.

The authors concluded that IQs in persons with AN are at least as high as the average IQ found in the normative population. They also made 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, raising the question about the influence of this factor on treatment and recovery.