Delayed Sleep Phase Syndrome

Delayed sleep phase syndrome, also known as delayed sleep phase disorder (DSPD) or delayed sleep–wake phase disorder, is a slowed down circadian rhythm or biological clock compared to those of social norms. The disorder affects the timing of biological rhythms: sleep, peak alertness, core body temperature, and hormonal cycles. People with this disorder are often called night owls. DSPD is a category of circadian rhythm sleep-wake disorder (CRSWD). There’s some disagreement about this diagnosis, since many insomnia-related disorders show up differently in people and circadian rhythm disorders and melatonin-related disorders are not well understood. The orexin system was only identified in 1998, yet it appears intimately implicated in our sleep-wake systems.

Multiple studies have provided evidence for the plasticity of our circadian rhythm cycle. In one, 15 volunteers spent 40 days and nights underground in a French cave, with their sleep-wake cycles monitored. Results found significant individual divergence,, with most participants settling upon a rhythm of 30 ± 4 hours. Researchers speculate lack of exposure to natural sunrise/sunset cycles is the cause of many circadian disorder symptoms — as in modern habits of spending extended periods indoors, without sunlight exposure and with artificial light. Symptom management may be possible with therapeutic drugs such as orexin antagonists or melatonin receptor agonists, as well as regular outdoor exercise. There may be a genetic component to the syndrome.