Are biological rhythms disturbed in depression?

Area of Science:

• Chronobiology
• Neuroendocrinology
• Psychiatry

Background:

• Circadian rhythm disturbances are implicated in endogenous depression.
• Previous research suggests phase-advances and free-running rhythms in depressed individuals.

Purpose of the Study:

• To investigate circadian rhythm characteristics in patients with endogenous depression.
• To compare circadian rhythms between depressed states, recovered states, and healthy controls.

Main Methods:

• Large-scale investigation of circadian rhythms, including depression scales, body temperature, and cortisol levels.
• Comparison of rhythm parameters (amplitude, acrophase) across different patient states and controls.

Main Results:

• No free-running rhythms or phase-advances were observed in depressed patients compared to controls or their recovered state.
• A reduction in the amplitude of depression scales and body temperature rhythms was noted.
• An increased amplitude of the cortisol rhythm, particularly at its circadian maximum, was found, correlating with diurnal depression severity.
• Coincidence of acrophases for depression scores and cortisol rhythm during depression suggests a shared circadian modulation.

Conclusions:

• Circadian rhythms themselves do not appear fundamentally altered in endogenous depression.
• Cortisol rhythm amplitude increase, potentially due to stress-induced masking, is linked to depression severity.
• A hypothalamic clock-like mechanism may modulate both the depressive illness process and the hypothalamo-pituitary-adrenocortical system activity.