Diurnal preference, sleep habits, circadian sleep propensity and melatonin rhythm in healthy human subjects.
Level 4 - case-series / case-control
Cross-sectional physiological laboratory study
PubMed 10675795 · doi:10.1016/s0304-3940(00)00793-x
What was done
Following 24 hours of sleep deprivation, 33 healthy young subjects completed a 26-hour ultra-short sleep-wake schedule (10 minutes sleep opportunity every 20 minutes) to evaluate circadian sleep propensity. Melatonin concentrations were sampled hourly throughout the protocol, and relationships between diurnal preference, habitual sleep timing, melatonin peak, and sleep propensity onset were evaluated.
What was found
Morning preference correlated significantly with earlier habitual sleep onset (r = -0.41, P = 0.04), earlier habitual sleep offset (r = -0.52, P = 0.002), earlier melatonin peak time (r = -0.36, P = 0.04), and earlier sleep propensity onset time (r = -0.36, P = 0.04). The intervals between habitual sleep midpoint and melatonin peak time, and between habitual sleep midpoint and sleep propensity onset time, were significantly longer in morning-preference subjects than in evening-preference subjects (P < 0.05).
Why it matters
This study demonstrates that diurnal preference is linked to differences in the physiological phase relationship between habitual sleep timing and the internal circadian pacemaker, rather than simple shifts in sleep schedule alone.
Limits
The study evaluated a small sample of 33 healthy young individuals, limiting generalizability to older or clinical populations. The prior 24-hour sleep deprivation may confound baseline physiological responses. Precise mean values and intervals were not reported in the abstract.
Cited by
- contradicts Endogenous melatonin begins rising roughly two hours before habitual sleep time, peaks about one hour into sleep, and reaches its lowest level about two hours after waking.