What hormone is involved in the connection between stress, circadian rhythms, and depression?

Cortisol is a glucocorticoid hormone that plays a crucial role in the body's response to stress. When an individual experiences stress, cortisol is released from the adrenal glands as part of the hypothalamic-pituitary-adrenal (HPA) axis. This hormone helps mobilize energy and regulate various bodily functions to cope with the stressful situation.

Cortisol also has significant implications for circadian rhythms—the body's natural sleep-wake cycle. Typically, cortisol levels rise in the early morning to help promote wakefulness and decrease throughout the day, reaching their lowest point at night. Disruptions in this rhythmic pattern can lead to sleep disturbances and negatively impact mood, both of which are closely linked to depression.

Research indicates that chronic stress often results in elevated cortisol levels, which can have detrimental effects on mood and emotional regulation. Prolonged exposure to high levels of cortisol has been associated with the development of depressive symptoms, highlighting its pivotal role in the interplay between stress, circadian rhythms, and depression. This makes it the most relevant hormone among the given choices in understanding these interconnected processes.