Delayed sleep phase disorder

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Delayed sleep phase disorder (DSPD), also called delayed sleep phase syndrome and delayed sleep–wake phase disorder, is the delaying of a person's circadian rhythm (biological clock) compared to those of social norms. The disorder affects the timing of biological rhythms, including sleep, peak period of alertness, core body temperature, and hormonal cycles. People with this disorder are often called "night owls". It is considered a kind of circadian rhythm sleep disorder. Multiple studies have found evidence for the plasticity of human circadian rhythm cycles. In one example, 15 volunteers spent 40 days and nights underground in a cave while researchers monitored their periods of waking and sleeping. Their results found significant divergence between individuals, with most participants settling upon a rhythm of 30 ± 4 hours. Researchers have speculated that the lack of exposure to natural sunrise/sunset cycles relates many of these circadian disorders' symptoms to modern habits of humans...

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