Cortisol peak at night is normal

Waking up at night around three o'clock does not necessarily indicate a sleep disorder. At this time, the body releases its peak of cortisol, a hormone that helps regulate wakefulness, precisely when sleep becomes lighter.

Study on circadian rhythms

In November 2022, researchers from the Oregon Health and Science University identified the exact moment when cortisol rises in the body, according to a study published in Frontiers in Neuroscience. Their method involved gradually shifting the internal clocks of volunteers day by day to separate the effects of sleep from those of the circadian rhythm, a rare technique in laboratory settings.

Forced desynchronization protocol

The researchers measured this hormonal peak in 34 adults, including 20 women, using a protocol called forced desynchronization. Volunteers' bedtime schedules changed every day by a few hours, allowing scientists to track the body’s internal clock through salivary melatonin levels collected continuously.

Cortisol peaks at specific time

The teams measured cortisol levels upon waking, regardless of the time. The hormonal response peaks around 3:40 a.m. in internal time, according to the study. This peak disappears by the end of the afternoon and at the beginning of the evening. The hormone’s levels increase further when waking occurs approximately three hours earlier than usual.

Rhythm not caused by fatigue

The circadian rhythm of cortisol persists even after adjusting for the previous night’s sleep, which rules out simple accumulated fatigue as the cause. Sleep does not flow uniformly, and this hormonal rise occurs at the worst possible moment for rest, according to the findings.