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New research from the University of Otago reveals that stress hormones like cortisol do not surge in one long wave but instead arrive in steady, hourly pulses that regulate metabolism, mood, and energy throughout the day. The study, conducted on mice and rats, found that brain cells responsible for releasing corticotropin-releasing hormone (CRH) in the hypothalamus fire rhythmically every 60 minutes, a pattern closely mirroring cortisol spikes observed in healthy adults.
Using an advanced technique called fiber photometry, researchers observed glowing CRH neurons in freely moving animals over several days, detecting sharp bursts of neural activity about once every hour. These bursts typically preceded brief wakefulness bouts and increased stress hormone release, acting as a natural “wake-up” signal to prepare the body for change even in the absence of immediate threats.
Interestingly, this hourly cycle, classified as an ultradian rhythm because it repeats more than once in 24 hours, operates independently from the well-known circadian clock that regulates daily cycles. The findings suggest additional internal checkpoints modulate whether these neural pulses cause systemic hormone surges, involving the pituitary and adrenal glands.
This nuanced understanding of stress hormone timing has wide implications. In conditions like depression, chronic stress, and adrenal insufficiency, this rhythm is often disrupted, leading to erratic energy, sleep, and mood patterns. The research supports clinical trials that use microdoses of hydrocortisone following natural pulse patterns, showing improved patient outcomes compared to standard dosing regimens.
Looking forward, the discovery opens pathways for rhythm-based diagnostics and therapies in psychiatry and sleep medicine. Wearable devices that monitor and regulate cortisol pulsatility could emerge to detect and correct disrupted stress rhythms early, potentially reducing the burden of mood disorders with fewer side effects than current hormone suppression methods.
The study was published in the Proceedings of the National Academy of Sciences.
Disclaimer: This article summarizes findings from preclinical studies in animals and ongoing clinical research. While the results provide important insights into the timing of stress hormone release, direct translation to humans requires further investigation. Readers with health concerns should consult medical professionals before making treatment decisions.
