What is the Origin of Phase Delay?

The term combines "phase," referring to a specific point in a cyclical pattern, and "delay," indicating a postponement of that specific point in time. Its use originates from early, foundational studies of circadian rhythms, where researchers observed that light exposure in the late subjective night or early subjective morning could cause a significant shift in the timing of the master biological clock, the suprachiasmatic nucleus (SCN). This temporal concept is foundational to understanding the entrainment of biological oscillators to the external 24-hour day.

What is the Mechanism of Phase Delay?

The mechanism is primarily mediated by the effects of external time cues, or zeitgebers, most importantly light, on the

Phase Delay

Meaning

Phase delay, in the context of chronobiology and hormonal health, refers to a persistent shift in an individual’s circadian rhythm to a later time, effectively postponing the timing of sleep, wakefulness, and associated physiological events. This temporal shift is characterized by a later onset of the nocturnal melatonin secretion and a later nadir of core body temperature, which are key markers of the internal biological clock. Clinically, a significant, persistent phase delay is the defining feature of Delayed Sleep Phase Syndrome (DSPS), a common circadian rhythm disorder that can profoundly impact metabolic and endocrine function due as a result of chronic misalignment between the internal clock and external time cues. It represents a fundamental temporal dysregulation of the neuroendocrine cycle.