Circadian period lengths of core body temperature and salivary melatonin in delayed sleep phase disorder and non-24-hour sleep-wake disorder

Delayed Sleep Phase Disorder (DSPD) is defined as an abnormally late sleep period (e.g. 3 am-noon) and is associated with significant morbidity. Individuals and therapy-based attempts to establish a desired earlier sleep period often fail. Although patients with DSPD indicate delayed circadian rhythms, the difficulty advancing the sleep period to an earlier time may arise from a longer endogenous circadian rhythm period length (i.e., tau). This study therefore aimed to measure circadian taus in DSPD disorder relative to normally entrained good sleepers.