Sleep Chronotypes are genetically determined, individual preferences for the timing of sleep and wakefulness, reflecting variations in the intrinsic period of the individual’s circadian rhythm. These biological preferences categorize individuals, most commonly, as “morning types” (larks), “evening types” (owls), or intermediate types. An individual’s chronotype significantly influences the optimal timing of their hormonal secretion, peak cognitive performance, and metabolic efficiency throughout the 24-hour cycle. Clinical adherence to one’s natural chronotype is crucial for maintaining circadian rhythm integrity and overall metabolic and hormonal health.
Origin
The term combines “sleep” with “chronotype,” derived from the Greek chronos (time) and typos (model or type). This concept emerged from the field of chronobiology, following research that quantified the individual differences in the timing of the internal biological clock. Early studies utilized questionnaires and later molecular markers, such as the timing of the dim-light melatonin onset (DLMO), to objectively classify these variations.
Mechanism
The underlying mechanism is governed by polymorphisms in the core clock genes, which subtly alter the intrinsic period of the endogenous circadian pacemaker in the suprachiasmatic nucleus (SCN). For instance, a “morning type” possesses a slightly shorter intrinsic cycle, causing their biological night to end earlier and their hormonal rhythms to peak earlier. This genetic variation dictates the timing of the nocturnal melatonin peak and the diurnal cortisol rhythm. Misalignment between an individual’s chronotype and their social or work schedule, often referred to as social jetlag, can disrupt hormonal signaling and impair metabolic function.
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