What hormonal change contributes to insomnia as stated in the mechanism of increased HPA axis activity?

Increased activity of the hypothalamic-pituitary-adrenal (HPA) axis is associated with elevated levels of stress hormones, specifically cortisol and catecholamines. Cortisol, a glucocorticoid produced by the adrenal glands, plays a crucial role in the body’s stress response. Under stress, the HPA axis stimulates the release of corticotropin-releasing hormone (CRH), which prompts the pituitary gland to secrete adrenocorticotropic hormone (ACTH), ultimately leading to an increase in cortisol production.

Elevated cortisol levels, especially when released in a circadian rhythm that is disrupted, are linked to disturbed sleep patterns and insomnia. Cortisol can interfere with the body's natural sleep-wake cycle, making it harder to fall asleep or stay asleep. Furthermore, increased catecholamines (like adrenaline and noradrenaline) can heighten physiological arousal and anxiety, further exacerbating difficulties with sleep.

Understanding this mechanism is vital for recognizing how chronic stress or conditions that cause prolonged activation of the HPA axis can lead to insomnia, as the body remains in a heightened state of alertness due to these hormonal fluctuations.