IS THERE A SEASONAL PATTERN OF RELAPSE IN BIPOLAR AFFECTIVE-DISORDERS- A DUAL NORTHERN AND SOUTHERN-HEMISPHERE COHORT STUDY

Background. Admission statistics for mania frequently show an increase in the summer. The present two-centre study was designed to test the hypothesis, in a representative sample of bipolar patients, that manic and depressive relapses show a seasonal pattern. Method. Two cohorts of bipolar I patients, one in London, England (n=86), the other in Dun edin, New Zealand (n=58), were tracked retrospectively during 1985-88 and prospectively during 1989-91, with the onset of all relapses being carefully dated. Results. In the London cohort there were 221 episode s of mania and 76 of depression; in the Dunedin cohort there were 201 of mania and 61 of depression. No consistent seasonal pattern of mania was detected in either centre. There was an autumn preponderance of d epressive episodes in both centres. Conclusions. Relapse of bipolar de pression, but not of mania, appears to be determined in part by season al factors.