Replicable differences in preferred circadian phase between bipolar disorder patients and control individuals.

Morningness/eveningness (M/E) is a stable, quantifiable measure reflecting preferred circadian phase. Two prior studies suggest that bipolar I disorder (BP1) cases are more likely to have lower M/E scores, i.e., be evening types compared with control groups. These studies did not recruit controls systematically and did not evaluate key clinical variables. We sought to replicate the reported associations in a large, well defined sample, while evaluating potential confounding factors. Adults with bipolar disorder (BP) were compared with community controls drawn randomly from the same residential areas (190 cases and 128 controls). M/E was evaluated using the composite scale of morningness (CSM). After accounting for variables correlated with M/E, BP cases had significantly lower CSM scores than controls (i.e., more evening-type or fewer morning-type). There were no significant differences in M/E scores between BP1 or BP2 disorder cases (n=134 and 56, respectively). CSM scores were stable over approximately 2 years in a subgroup of participants (n=52). Individuals prescribed anxiolytic drugs, antidepressants, antipsychotic drugs, mood stabilizers or stimulant drugs had significantly lower age-corrected CSM scores compared with persons not taking these drugs. BP cases are more likely to be evening types, suggesting circadian phase delay in BP cases. Individuals with elevated depressive mood scores are more likely to be evening types. Our results suggest a replicable relationship between circadian phase and morbid mood states.