Perimenopause doesn't just disrupt sleep it disrupts the biological clock that controls sleep. As oestrogen declines, it weakens the suprachiasmatic nucleus, the brain's master circadian clock, and reduces melatonin production. The result earlier morning waking, difficulty falling asleep, and a flattened sleep-wake rhythm. This article explains the science behind circadian disruption in perimenopause and the evidence-backed strategies morning light, CBT-I, and consistent wak