For true night owls, a normal workday feels like permanent jet lag
Some people cannot fall asleep until hours after midnight, however hard they try, yet drift off at the same late hour every night and sleep perfectly well. Their body clock is simply shifted later than society's. Forced onto a nine-to-five schedule, they live in what researchers call social jet lag.
Delayed sleep phase disorder is a circadian rhythm disorder in which the whole internal clock runs late. It shifts not only sleep but the peak of alertness, the daily rise and fall of body temperature, and hormone cycles. Left to their own timetable, sleeping perhaps from 4 a.m. to 1 p.m., people with it can rest normally and feel fine during their waking hours. The trouble is getting up for school or work.
It is easy to mislabel. The condition accounts for 7 to 13 percent of complaints of chronic insomnia, yet many doctors know little about it, so it is often mistaken for ordinary insomnia or a psychiatric problem. Specialists still argue over how to diagnose it, partly because sleep science keeps revealing new pieces: the orexin system, now considered central to sleeping and waking, was only identified in 1998. There may be a genetic component, and genetic studies link it with ADHD, many of whose patients have the delayed pattern.
Human rhythms are surprisingly flexible. In one experiment, 15 volunteers spent 40 days and nights in a French cave without daylight, and most drifted to cycles of about 30 hours, though individuals varied widely. Researchers suspect modern life, spent largely indoors under artificial light and away from sunrise and sunset, may contribute to such disorders.
About half of reported patients have depression or other psychological difficulties, roughly the same share as in chronic insomnia, and no single psychiatric category fits them. Whether one causes the other is unclear. The unusual hours can bring social disapproval, and sleep researcher Michael Terman has suggested that people who follow their own internal clocks may be less prone to depression than those forcing themselves onto a different schedule.
Source: Delayed sleep phase disorder
