Do cortisol levels usually dip near midnight and rise later in sleep, while night waking and variable energy remain nonspecific?

Cortisol follows a robust daily pattern, but its timing is governed by both internal circadian phase and actual sleep–wake behavior. In a 64-year-old woman, night waking or fluctuating energy should therefore be interpreted as nonspecific symptoms rather than evidence of a cortisol-timing disorder.

Clinical and timing evidence

• High-frequency 24-hour sampling in healthy adults placed the mean cortisol nadir at 00:18 (95% CI 23:39–00:58). For conventional sleep schedules, “near midnight” is an accurate approximation, although not a fixed universal clock time.
• Cortisol usually begins to rise at approximately 02:00–03:00, during the latter part of sleep, and peaks around the sleep–wake transition.
• The cortisol awakening response is a related but distinct phenomenon: cortisol commonly rises further and peaks about 30–45 minutes after waking. Thus, sampling time must be interpreted relative to awakening, not simply by clock time.

Mechanistic considerations

• The overnight increase reflects substantial endogenous circadian regulation, modified by sleep onset, sleep stage, light–dark timing, and awakening.
• Schedule shifts can change the observed cortisol nadir more rapidly than the underlying circadian system adapts, producing apparent timing changes without a simple symptom signature.

Interpreting night waking and variable energy

• Insomnia studies show heterogeneous findings—higher evening, early-night, or morning cortisol in some cohorts, but no difference or lower awakening cortisol in others. No pattern is specific to sleep-maintenance waking.
• Poor sleep and fatigue may correlate with a flatter next-day cortisol slope in selected populations, but these associations do not establish causation or identify circadian mistiming.

Bottom line

• The claim is well supported: cortisol is typically lowest around midnight/early sleep and rises before waking, but night waking and variable energy alone cannot diagnose a mistimed cortisol rhythm. Assessment requires repeated, accurately time-stamped measurements interpreted alongside sleep timing and, when relevant, an independent circadian-phase marker.