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Melatonin light super-sensitivity identified in bipolar I disorder
By Liam Davenport, MedWire News
15 October 2009
Acta Neuropsychiatrica 2009; 21: 246?255
Patients with bipolar I disorder have melatonin super-sensitivity to light compared with healthy individuals, which may serve as an endophenotypic marker for the condition, conclude Australian researchers.
Several studies have suggested that bipolar disorder patients have super-sensitivity to light at night, with plasma melatonin levels suppressed more than in patients with other affective disorders and healthy individuals. However, the findings have not been supported by all investigations, with some suggesting sensitivity in only bipolar I disorder patients.
To examine melatonin sensitivity to light over a range of light intensities, Karen Hallam, from the University of Melbourne in Victoria, and colleagues studied seven patients with bipolar I disorder and 34 healthy controls.
The participants were administered a series of questionnaires and then attended 1 to 4 testing nights separated by at least a 7-day recovery period, with melatonin levels measured in blood samples obtained throughout the night. They were kept in complete darkness between 21:00 h and 24:00 h, exposed to light intensities of 0, 200, 500, and 1000 lux between 24:00 h and 01:00 h, and then returned to complete darkness for the remainder of the night.
During zero light conditions, there were no significant differences in the changes in melatonin levels between patients and controls. However, during exposure to 200, 500, and 1000 lux, patients showed significantly more sensitivity to light than controls, with the sensitivity consistently elevated across the light?response curve.
Sensitivity to light was dose-dependent in both groups, with a regression analysis indicating that patients and controls had a similar regression slope, although it was steeper for patients than controls., Bipolar disorder patients had a significantly greater rebound in melatonin levels 30 minutes following the light being turned off, although this difference had been eliminated by 60 minutes, the team notes in the journal Acta Neuropsychiatrica.
They write: ?This study further investigates the usefulness of melatonin super-sensitivity to light as an endophenotypic marker of bipolar disorder. The use of endophenotypic markers that integrate both clinical and biological observations may provide a powerful tool to target genetic, molecular, and behavioral changes in the disorder. Ideally, these observations will inform both etiological and neurobiological studies of the disorder and ultimately improve clinical treatment of the illness.?
Free abstract
By Liam Davenport, MedWire News
15 October 2009
Acta Neuropsychiatrica 2009; 21: 246?255
Patients with bipolar I disorder have melatonin super-sensitivity to light compared with healthy individuals, which may serve as an endophenotypic marker for the condition, conclude Australian researchers.
Several studies have suggested that bipolar disorder patients have super-sensitivity to light at night, with plasma melatonin levels suppressed more than in patients with other affective disorders and healthy individuals. However, the findings have not been supported by all investigations, with some suggesting sensitivity in only bipolar I disorder patients.
To examine melatonin sensitivity to light over a range of light intensities, Karen Hallam, from the University of Melbourne in Victoria, and colleagues studied seven patients with bipolar I disorder and 34 healthy controls.
The participants were administered a series of questionnaires and then attended 1 to 4 testing nights separated by at least a 7-day recovery period, with melatonin levels measured in blood samples obtained throughout the night. They were kept in complete darkness between 21:00 h and 24:00 h, exposed to light intensities of 0, 200, 500, and 1000 lux between 24:00 h and 01:00 h, and then returned to complete darkness for the remainder of the night.
During zero light conditions, there were no significant differences in the changes in melatonin levels between patients and controls. However, during exposure to 200, 500, and 1000 lux, patients showed significantly more sensitivity to light than controls, with the sensitivity consistently elevated across the light?response curve.
Sensitivity to light was dose-dependent in both groups, with a regression analysis indicating that patients and controls had a similar regression slope, although it was steeper for patients than controls., Bipolar disorder patients had a significantly greater rebound in melatonin levels 30 minutes following the light being turned off, although this difference had been eliminated by 60 minutes, the team notes in the journal Acta Neuropsychiatrica.
They write: ?This study further investigates the usefulness of melatonin super-sensitivity to light as an endophenotypic marker of bipolar disorder. The use of endophenotypic markers that integrate both clinical and biological observations may provide a powerful tool to target genetic, molecular, and behavioral changes in the disorder. Ideally, these observations will inform both etiological and neurobiological studies of the disorder and ultimately improve clinical treatment of the illness.?
Free abstract
