30/03/2026
Your hormones don’t just “exist” they follow a tightly controlled 24-hour pattern (your circadian rhythm). Cortisol should peak in the early morning to wake you up, then gradually fall across the day. Melatonin should rise in the evening to prepare your body for sleep. When sleep is poor, short, broken, or mistimed this rhythm gets disrupted. Cortisol can stay elevated into the evening (leaving you “tired but wired”), while melatonin release is blunted or delayed. The result is a system that never fully switches off, keeping the body in a low-grade stress state.
This disruption doesn’t stay isolated, it spills into your metabolic hormones. Poor sleep increases Ghrelin (which drives hunger) and reduces Leptin (which signals fullness). At the same time, your response to insulin becomes less efficient, meaning your body is more likely to store energy rather than use it. This is why after a bad night’s sleep, you’re not just more tired you’re biologically driven to eat more, crave quick energy, and store fat more easily.
In perimenopause, this system becomes even more sensitive. Fluctuating levels of Estrogen and Progesterone directly affect sleep quality. Progesterone has a naturally calming, sleep-supportive effect so as it declines, many women notice lighter, more fragmented sleep. Estrogen also influences temperature regulation and serotonin, so fluctuations can trigger night waking, hot flushes, and reduced sleep depth. Poor sleep then feeds back into cortisol dysregulation, creating a loop: worse sleep → higher stress hormones → more disrupted sleep. It can feel like your whole system has been hijacked.
For men, especially those doing shift work, the disruption often shows up differently but is just as significant. Irregular sleep timing and light exposure can blunt testosterone production, which is closely tied to deep sleep and peaks at night. This impacts recovery and mood, energy and body composition. It also messes with our cortisol pattern, meaning a less clear ‘on and off’ signal.
Poor sleep is where a lot of people feel like their body has ‘suddenly changed’.
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