Superior Academic Performance Linked to Increased Risk for Bipolar Disorder

Pauline Anderson

February 11, 2010

February 11, 2010 (Updated with comment February 17, 2010) — Students who at the age of 16 years excel at school, particularly in creative subjects, are almost 4 times more likely to develop bipolar disorder during the next decade than teenagers with average grades, a new study has found.

This finding supports the hypothesis that creative individuals are more susceptible to bipolar disorder, lead author James H. MacCabe, PhD, Senior Institute of Psychiatry, King’s College, London, United Kingdom, told Medscape Psychiatry. "This is an idea that a lot of people believe, although until this study, there hasn’t been very strong evidence," said Dr. MacCabe.

However, the investigators also found a relationship, albeit a weaker one, between students who do poorly in school and the later development of bipolar disorder.

The study is published in the February issue of the British Journal of Psychiatry.

Healthy Cohort at Baseline

For the study, researchers followed up 713,876 children who were in the Swedish national school register from 1988 to 1997. The researchers excluded students who developed a psychiatric disorder before or within 1 year after completion of their national examination, which all Swedish children must sit the year they turn 16 years old.

"We didn’t want to risk that we were capturing people who were already ill and whose school performance might have been affected by their illness," said Dr. MacCabe. "We wanted to get people when they were still well and then follow them up."

From the national examination, students receive grades ranging from A to E in each of 16 compulsory subjects, which are converted into grade point averages. In this study, grade point average scores ranged from 1.0 to 5.0, with means of 3.11 for boys and 3.39 for girls.

Researchers followed up the subjects until December 31, 2003. The mean follow-up period was 9.48 years, by which time the mean age of the study group was 26.48 years.

During the follow-up period, 280 young people developed bipolar disorder, with a mean age at onset of 20.79 years. There were roughly an equal number of men and women who developed the disorder. Information on bipolar disorder diagnoses came from the Swedish hospital discharge register that contains details of all psychiatric hospitalizations.

Association Stronger in Boys

Students in the highest academic category — with grades of 2 or more standard deviations above the mean — had a significantly higher risk for bipolar disorder (hazard ratio, 3.79) compared with those with average scores.

"Basically, these students who got mainly A grades and a few B's thrown in had a 4-fold increased risk of subsequently developing bipolar disorder,” said Dr. MacCabe.

At the other end of the academic scale, those in the lowest grade category were also more likely to develop bipolar disorder than those with average scores (hazard ratio, 1.86).

"The people who were 2 standard deviations below the mean, so mostly D and E grade students, were about twice as likely to get bipolar disorder," said Dr. MacCabe. Adjusting for parental education and socioeconomic status did not fully explain these relationships, he added.

Although there were more girls than boys in the top academic category, the relationship between scholastic achievement and bipolar disorder appeared to be stronger in boys than girls. The study authors noted, too, that most of the eminent creative historical figures with probable bipolar disorder were male.

"The men in this top category were a more extreme group in that they were doing much better [academically] than their peers," said Dr. MacCabe. "Perhaps the more extreme, the more different you are than your peers in terms of school performance, the higher your risk."

Striking Comparison to Schizophrenia

The study gives credence to the idea that creative people are more susceptible to bipolar disorder. Although scoring an A grade was associated with an increased risk for bipolar disorder for all 16 school subjects, the association was stronger for the humanities than for science and technical subjects.

In contrast to bipolar disorder, higher academic marks are associated with decreased risk for schizophrenia, the study authors noted. That’s "very striking" in light of a recent theory that schizophrenia and bipolar disorder are more closely genetically linked than previously believed, commented Dr. MacCabe. "This seems to suggest that we found something that distinguishes between schizophrenia and bipolar, at least in some cases."

The study compares the development of bipolar disorder with academic achievement not IQ. Intelligence is only 1 factor that influences academic success, with other factors including memory, attention, motivation, diligence, and organization skills. Recent research has shown that only about 60% of school performance is related to IQ, said Dr. MacCabe.

The study could have been biased toward more severe cases because it included only hospital-treated bipolar disorder. Other possible biases were that students with higher IQ might have been more likely to seek psychiatric treatment or psychiatrists may have been more apt to diagnose bipolar disorder in a student with a high IQ.

Although the study authors attempted to ensure that all students did not have bipolar disorder at the time of their examination, it is possible that some had subclinical symptoms of hypomania or depression, and this could have influenced their performance.

People who are genetically predisposed to bipolar disorder but have not become ill may have certain cognitive styles, for example, the ability to concentrate, that might enhance their academic performance, said Dr. MacCabe.

"We know that bipolar disorder is a strongly genetic disorder. Those people would have been carrying their genetic predisposition for the disorder, and it may have manifested itself in this way by actually improving their scores in school."

High Marks, High IQ Not the Same

Commenting on the study, Stephen Strakowski, MD, University of Cincinnati, Ohio, said the study is generally well done and adds to emerging evidence that bipolar disorder may be associated with higher intelligence.

However, he noted 2 major limitations. First, because the definition of IQ used in the study is based on Swedish educational tests, it is a better measure of school performance than raw intelligence.

"Although school performance and intelligence are often highly correlated, they are not the same, as we know from a number of historic 'geniuses' who did not do well in school," he told Medscape Psychiatry.

Second, said Dr. Strakowski, the bipolar diagnoses the researchers used were determined by clinicians rather than through structured interviews. "Consequently, if the clinicians assumed that smarter patients were more likely to suffer from bipolar disorder, then there is a bias towards the very association the authors are investigating."

Dr. Strakowski also noted that although the odds ratio for more "A" students in the bipolar group was relatively high, the actual percentage of these students in the total bipolar population was still low. "Consequently, the results are modest but do add importantly to this literature," he said.

The study authors have disclosed no relevant financial relationships.

Br J Psychiatry. 2010;196:109-115.

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