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The association between school exam grades and subsequent development of bipolar disorder

Abstract Objective Prior studies have indicated that both high and low school grades are associated with development of bipolar disorder (BD), but these studies have not adjusted for parental history of mental disorder, which is a likely confounder. Furthermore, the association between school grades and bipolar I disorder (BD-I) has not been studied. Therefore, we aimed to study the association between school exam grades and subsequent development of BD and BD-I while adjusting for parental history of mental disorder. Methods We conducted a register-based nationwide cohort study following 505 688 individuals born in Denmark between 1987 and 1995. We investigated the association between school exam grades and development of BD or BD-I with a Cox model adjusting for family history of mental disorder and other potential confounders. Results During follow-up, 900 individuals were diagnosed with BD and 277 of these with BD-I. The risk for BD and BD-I was significantly increased for individuals not having completed the exams at term [adjusted hazard ratio (aHR) for BD (aHR=1.71, 95% CI: 1.43–2.04) and for BD-I (aHR=1.57, 95% CI: 1.13–2.19)]. Also, having low exam grades in mathematics was associated with increased risk of both BD (aHR=2.41, 95% CI: 1.27–4.59) and BD-I (aHR=2.71, 95% CI: 1.41–5.21). Females with very high exam grades in Danish (percentile group>97.7) had a significantly increased risk of BD-I (aHR=2.49, 95% CI: 1.19–5.23). Conclusions The potential to develop BD seems to affect the school results of individuals negatively even before BD is diagnosed – with females having the potential to develop BD-I as a possible exception.