Nocturnal melatonin and 24-hour 6-sulphatoxymelatonin levels in various phases of bipolar affective disorder.

Nine bipolar patients (2 men and 7 women) and 12 healthy control subjects completed overnight sampling for serum melatonin (MT) and urinary 6-sulphatoxymelatonin (aMT6s). The patients were investigated during manic, depressed, and/or euthymic states. Although serum MT levels did not differ significantly across the bipolar groups, in all cases serum MT levels were significantly lower than in control subjects. Differences in MT levels were also present between bipolar patients who were in a depressed phase and control subjects. There were no statistically significant differences in urinary aMT6s levels among the patients and control subjects, although in all cases nocturnal aMT6s levels were significantly higher than daytime levels. This study provides tentative evidence for decreased serum MT as a trait but not a state marker in bipolar affective disorder.