medwireNews: Depressive symptoms in patients with bipolar disorder are at a minimum during the summer but peak in the winter, shows a prospective analysis that monitored patients for at least 10 years.
Manic symptoms, on the other hand, tended to peak at about the time of the autumn equinox, particularly in patients with bipolar II disorder.
"Clinicians should heed these higher risk periods and identify seasonal patterns within individual patients to target appropriate treatment," say lead researcher Jess Fiedorowicz (Roy J and Lucille A Carver College of Medicine, Iowa City, USA) and colleagues.
The study included 202 patients with bipolar II disorder, who, on average, spent 1.6% of the weeks in each month with clinically significant hypomanic symptoms. These peaked in August and September, at 2.2% and 2.4%, respectively. A further 112 patients with bipolar I disorder spent an average 10.7% of the weeks in each month with manic symptoms, which also peaked during August and September. This peak was less marked than in the bipolar II disorder patients, but was still statistically significant.
By contrast, depressive symptoms were at their lowest at this time of year, at about 40% of weeks per month in July and August for bipolar I disorder and about 30% in July and October for bipolar II disorder. Depressive symptoms peaked during the winter in both groups of patients, at about 42% in December and January in bipolar I disorder and about 32% in January and February in bipolar II disorder.
"This pattern may be consistent with suggested links between hibernation and changes in sleep, energy, and behavior," comment the researchers in Bipolar Disorders.
Relapse from the initial episode followed a slightly different seasonal pattern. Patients with bipolar I disorder most often relapsed into a depressive episode in May and August and into a manic episode in March, July, and October. Those with bipolar II disorder mostly relapsed into depressive episodes in October and November and into hypomanic episodes in August.
Fiedorowicz et al observe that some of their findings contradict previous research, but say that theirs is the largest and longest prospective study to date.
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