Does latitude as a zeitgeber affect the course of bipolar affective disorder?

Bipolar disorder (BD) is characterized by recurrent episodes of mood dysregulations and depression is considered as the most frequent form of relapse. However, there is some evidence that in tropical countries, the course might be different with fewer depressive episodes. This study aims to examine the frequency of depressive and manic episodes in a sample of subjects with BD from India.

Index subjects and a reliable informant (a family member) were interviewed with Diagnostic Interview for Genetic studies and a life chart was drawn to ascertain the episodes of illness in addition to reviewing their clinical case records. The mean total episode frequency and the mean manic and depressive episode frequency were estimated for this study.

Data on the total episode number and number of manic and depressive episodes separately was available in 439 subjects. The subjects had been ill for 7.45 years, had experienced an average of 3.29 episodes of mania and 1.08 episodes of depression. Thus episodes of mania were seen to be more frequent.

It has been increasingly recognized that circadian rhythm abnormalities could play an important role in the relapse and symptom expression of bipolar disorder. The mania predominance in the course of BD in this population contrasts from the depressive predominance in other studies. We suggest that this phenomenon could be a function of latitudinal gradient in the expression of BD using the zeitgeber hypothesis.