Seasonality in a community sample of bipolar, unipolar and control subjects.
BACKGROUND
This study examined seasonality in a community sample of five diagnostic groups: normal subjects, those with non-seasonal depression (NSD), seasonal depression (SD), non-seasonal bipolar disorder (NSBD) and seasonal bipolar disorder (SBD).


METHODS
Telephone interviews were conducted across the Province of Ontario. Seasonal changes in mood and behaviour were determined using the Seasonal Pattern Assessment Questionnaire (SPAQ). Five additional seasonality items consisting of depressive symptoms were included in the interview. The mean global severity of seasonality (GSS) scores were obtained and the entire inventory of 11 seasonality items were compared across the identified groups.


RESULTS
The mean GSS score for the controls was 5.2 (S.D. = 4.0), 8.0 (S.D. = 4.9) for NSD, 10.5 (S.D. = 3.9) for SD, 10.5 (S.D. = 5.4) for NSBD and 13.4 (S.D. = 5.4) for SBD. These scores differed significantly (F = 61.68, df = 4, p < 0.001). For the majority of the individual items, the SBD group rated the highest degree of seasonal fluctuation, while the NSBD and SD groups had nearly identical item scores.


CONCLUSIONS
Limitations in this study include the relatively small number of subjects in the NSBD and SBD groups, and the inherent limitations in a telephone interview.


CONCLUSIONS
Individuals with bipolar disorder experience greater seasonality than those with depression or healthy controls. Even the non-seasonal bipolar group had as much seasonal fluctuation as the seasonal depression group, which has important implications for the management of bipolar illness.
Shin
Karen
K
Department of Psychiatry, University of Toronto, Canada.
Schaffer
Ayal
A
Levitt
Anthony J
AJ
Boyle
Michael H
MH
D000328:Adult; D001714:Bipolar Disorder / Q000523:psychology*; D016022:Case-Control Studies; D003866:Depressive Disorder / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010507:Periodicity; D016574:Seasonal Affective Disorder / Q000523:psychology; D012621:Seasons; D012720:Severity of Illness Index