Admission rates of bipolar depressed patients increase during spring/summer and correlate with maximal environmental temperature.
OBJECTIVE
We intended to identify a relationship, if exists, between various climatic factors and the admission rates of bipolar affective disorder depressed patients (BPD) or major depressive disorder patients (unipolar) (UPD) to psychiatric hospitals, as well as potential seasonal variability in hospitalization rates of this population.


METHODS
Data on admissions of ICD-9 BPD and UPD patients to Tel Aviv's seven public psychiatric hospitals during 11 consecutive years were collected along with concomitant meteorological information


RESULTS
Admissions of 4117 patients with BPD and 1036 with UPD who fulfilled our specific inclusion criteria were recorded. Bipolar depressed, but not UPD, patients exhibited significant seasonal variation (higher spring and summer versus winter mean monthly admission rates), and the admission rates of patients with BPD, but not UPD, correlated significantly with mean maximal monthly environmental temperature


CONCLUSIONS
Increased environmental temperature may be a risk factor for evolvement of major depressive episode in patients with bipolar disorder with psychiatric co-morbidity, at least in cases that necessitate hospitalization and at the examined geographic/climatic region of Israel. Further large-scale studies with bipolar depressed patients with and without co-morbid disorders are needed to substantiate our findings and to determine the role of seasonal and climatic influence on this population, as well as its relationship to the pathophysiology of bipolar disorder.
Psychiatric Division, Rambam Medical Center, Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel.
Avraham
A
Shapira
Roni
R
Shiloh
Oded
O
Potchter
Haggai
H
Hermesh
Miriam
M
Popper
Abraham
A
Weizman
D001714:Bipolar Disorder / Q000175:diagnosis* / Q000503:physiopathology; D002980:Climate; D003866:Depressive Disorder / Q000175:diagnosis*; D006801:Humans; D010343:Patient Admission / Q000706:statistics & numerical data*; D012621:Seasons; D013696:Temperature