This Lancet review looks at disorders where sleep timing is out of step with daily life, such as delayed sleep phase, jet lag and shift work disorder. It is a narrative review, not a new study. The work it cites spans newborns through older adults.
Its main point is that not every disrupted daily rhythm comes from the body clock alone. Sleep timing also reflects sleep pressure, behavior and surroundings. Current diagnosis cannot tell inner causes from outer ones.
Cited figures suggest delayed sleep phase is more common in teenagers (3.3 to 7.3% of adolescents). In one trial, morning bright light plus evening light-blocking glasses shifted the body clock earlier by well over an hour (1 h 25 min), against a much smaller shift in controls. About a quarter of shift workers met formal criteria for shift work sleep disorder (approximately 27%).
The authors judge the evidence enough to weakly support evening melatonin for delayed sleep phase in children and adults, at doses described as ranging from 0.5 mg to 5 mg. Very few high-quality studies exist. Safety data for melatonin are lacking, especially for children, teens and pregnant people. The review did no formal quality rating.
The authors suggest that evening melatonin combined with morning light appears more effective than either one alone, given under clinical supervision.
Anyone wondering how this applies to them should talk to a clinician about their situation.
Source: Meyer N, Harvey A, Lockley S, et al.. Circadian rhythms and disorders of the timing of sleep. The Lancet (2022). doi:10.1016/s0140-6736(22)00877-7