“Is Bipolar Disorder More Common in Highly Intelligent People? A Cohort Study of a Million Men”, C R. Gale, G. D. Batty, A. M. McIntosh, D. J. Porteous, I. J. Deary, F. Rasmussen2013 (IQ, BP personality)⁠:

Anecdotal and biographical reports have long suggested that bipolar disorder is more common in people with exceptional cognitive or creative ability. Epidemiological evidence for such a link is sparse.

We investigated the relationship between intelligence and subsequent risk of hospitalization for bipolar disorder in a prospective cohort study of 1,049,607 Swedish men. Intelligence was measured on conscription for military service at a mean age of 18.3 years and data on psychiatric hospital admissions over a mean follow-up period of 22.6 years was obtained from national records.

Risk of hospitalization with any form of bipolar disorder fell in a stepwise manner as intelligence increased (p_{linear trend} < 0.0001). However, when we restricted analyses to men with no psychiatric comorbidity, there was a ‘reversed-J’ shaped association: men with the lowest intelligence had the greatest risk of being admitted with pure bipolar disorder, but risk was also elevated among men with the highest intelligence (p_{quadratic trend} = 0.03), primarily in those with the highest verbal (p_{quadratic trend} = 0.009) or technical ability (p_{quadratic trend} < 0.0001).

At least in men, high intelligence may indeed be a risk factor for bipolar disorder, but only in the minority of cases who have the disorder in a pure form with no psychiatric comorbidity.